J Plant Biotechnol (2024) 51:077-088
Published online April 9, 2024
https://doi.org/10.5010/JPB.2024.51.009.077
© The Korean Society of Plant Biotechnology
Correspondence to : e-mail: leila.ba.riahi@gmail.com
This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Pearl millet is a small-seeded staple crop in arid and semi-arid regions of Africa and Asia. It is the crop of choice in the hottest and driest climates where other cereals do not grow well and is considered a future climate-smart cereal. This underutilized cereal provides nutritional and food security to millions of people. It is also used as animal feed, fuel, and fodder as well as in brewing. The gluten-free grains of this cereal are rich sources of fats, proteins, carbohydrates, minerals, especially iron and zinc, and phenolics with health-promoting properties. Pearl millet also has industrial uses in the production of bioenergy, biodegradable products, bio-coagulants, and construction materials, and in tissue engineering. Pearl millet hybrids have gained considerable popularity among Indian farmers, resulting in a significant increase in production yields. However, pearl millet production in Africa is primarily dependent on traditional landraces with limited acceptance of improved open-pollinated varieties and hybrids. Consequently, no significant increase in pearl millet production has been achieved over the past few decades. Despite its inherent resilience against poor climates, this staple crop faces a complex array of abiotic and biotic stresses in its production areas, which is exacerbated by ongoing climate change. Furthermore, certain anti-nutritional traits impede its overall nutritional value and effective utilization. Hence, improving pearl millet is a continuous and significant challenge for plant breeders and biotechnologists.
Keywords Pearl millet, Gluten free, Smart cereal, Improvement, Climate change
Pearl millet (Pennisetum glaucum (L.) R.Br. syn. Cenchrus americanus (L.) Morrone) assumes a crucial role as a staple nutri-cereal crop in arid and semi-arid regions of Africa and Asia. Moreover, pearl millet is gaining prominence as forage and cover crop in countries such as Canada, the United States, Mexico, Central Asia, Brazil and Australia (Singh and Nara 2023). Globally, it is the sixth most important cereal crop in the world behind maize, rice, wheat, barley and sorghum and addresses the dietary requirements and socio-economic well-being of millions (Satyavathi et al. 2021). Pearl millet is acknowledged for its elevated nutritional and caloric characteristics which promoted its high potential as food, feed and forage. It serves as a primary dietary component, especially in developing nations, owing to its substantial levels of carbohydrates, proteins, fats, vitamins, and essential minerals, notably iron and zinc. Additionally, pearl millet is gaining popularity as functional foods throughout the world (Samtiya et al. 2023). Notably, this cereal is abundant in bioactive compounds with significant health-promoting potential, including phenolic acids, flavonoids, and dietary fiber (Triki et al. 2022). Pearl millet also exhibits significant potential as industrial crop with increasing interests in bioenergy production, textile engineering and the production of eco-friendly biodegradable products (Ben Romdhane et al. 2022).
Pearl millet stands out as one of the most heat-tolerant and resilient cultivated cereals, displaying remarkable drought, salinity and low soil fertility tolerance and has historically acted as a reliable source of sustenance in areas experiencing unpredictable climate patterns (Meena et al. 2020). It holds
significant importance as a major food crop for smallholder subsistence farmers residing in the semi-arid tropical regions of Africa and Asia (Pucher et al. 2016). This under-utilized crop, have superior resilience to drought and heat stress than wheat and is considered a model crop for abiotic stress tolerance studies (Ghatak et al. 2021). Its drought tolerance, rapid growth, and low-input requirements have positioned it as a lifeline for smallholder farmers against food insecurity and poverty in arid ecosystems and make of it a climate-smart cereal with substantial potential in the future in the context of the ongoing climatic changes (Hassan et al. 2021).
Despite pearl millet’s remarkable resilience to abiotic stresses and its substantial nutritional value, the imperative for its improvement remains an ongoing challenge. Indeed, on-farm pearl millet yields tend to be consistently low, exhibiting significant variability even within the same farm (Diallo et al. 2019). Moreover, pearl millet is susceptible to diverse biotic stresses, including weeds along with fungal, viral, and bacterial infections (Chanwala et al. 2022). Therefore, the enhancement of pearl millet’s tolerance to both abiotic and biotic stress, the biofortification of its nutrient profiles, and the resolution of prevailing constraints that hinder its full potential can further enhance the significance of pearl millet as a nutri-cereal and industrial crop with diversified products and uses. This will secure its ongoing role in bolstering food security within arid regions; characterized by new and increasingly challenging environments, as well as an unprecedented population increase.
Pearl millet (Pennisetum glaucum (L.) R.Br. syn. Cenchrus americanus (L.) Morrone) represents an annual C4 and diploid (2n = 2x = 14) cereal belonging to the Poaceae family. This crop has a relatively small genome with DNA content of 1C = 2.36 pg (Martel et al. 1997). This robust and rapidly growing annual grass exhibits substantial morphological diversity, typically ranging from 1 to 3 meters in height, although it can attain heights up to 5 meters (Upadhyaya et al. 2008). Pearl millet is a highly cross-pollinated crop characterized by protogynous flowering. Traditional cultivars of this species form random-mating populations marked by considerable levels of heterozygosity and heterogeneity. Pollination primarily occurs through wind and insects, particularly by bees (Serba et al. 2019).
Pearl millet, traceable through archaeological records, stands as the most ancient African cereal and is intimately linked with the appearance of agriculture in West Africa (Burgarella et al. 2018). The domestication trajectory of pearl millet finds its origins over 4,000 years ago within the Sahel region of West Africa from its wild progenitor, Pennisetum violaceum (Lam.) Rich. [syn. P. americanum subsp. monodii (Maire) Brunken]. Later, this crop was expanded to East Africa and India (Fuller et al. 2021). The centre of origin and diversification is accepted to be within West Africa, where a persistent gene flow with its wild ancestor persists (Sattler and Haussmann 2020). Archaeological evidence highlighted the presence of fully cultivated pearl millet in Southeastern Mali by the second half of the third millennium BC and in eastern Sudan by the early second millennium BC (Winchell et al. 2018). The last authors reported that the dispersal of pearl millet to India took less than 1000 years. Later, the cultivation of this crop spread to various parts of the globe, including South Asia, Eastern and Southern Africa, facilitated by maritime trades. In approximately the 8th Century, the introduction of this cereal reached North African countries (Tostain 1998). Actually, pearl millet is mainly cultivated in Africa and India as staple cereal crop but also cropped in USA, Latin America, Canada and Australia as forage and cover crop (Sharma et al. 2021).
Pearl millet serves as a versatile cereal crop cultivated for various purposes, including grain, green fodder and stover. The species ranks sixth worldwide in terms of cultivation extent, after wheat, maize, rice, barley, and sorghum. It is a major staple crop for 90 million poor people and is cultivated on 27 million ha area in arid and semi-arid tropics of Asia and Africa. Interestingly, its significance is even more pronounced in African country and India. Pearl millet is one of the most important crops in the whole Sahelian region from Senegal to Sudan (Mariac et al. 2006). This crop ranks second in Senegal (Bastos et al. 2022) and fourth in Benin (Adeoti et al. 2017). In Niger, pearl millet covers more than 65% of the total cultivated area (Mariac et al. 2006). This crop stands as a dietary staple for over 70% of Namibia’s population (McBenedict et al. 2016) and is the most important summer crop in Southern Tunisia (Loumerem et al. 2008). In Sudan, 74% of dietary energy is derived from pearl millet (Boncompagni et al. 2018). In India, pearl millet is the third most widely cultivated food crop after rice and wheat (Kumar et al. 2020). Across arid and semiarid territories in Africa and Southern Asia, pearl millet plays a pivotal role in traditional farming systems and as a primary food source. Additionally, it finds utility as a temporary summer pasture or cover crop in the Americas and Australia (Serba et al. 2019).
Due to its remarkable photosynthetic efficiency and capacity for dry-matter production, pearl millet emerges as a preferred crop for farmers in challenging agroclimatic zones, where other cereals are likely to fail to produce economic yields (Satyavathi et al. 2021). This crop has a relatively short growth cycle which facilitates the practice of double cropping in many regions. Moreover, pearl millet has lower minimal optimal rainfall and higher maximal optimal temperatures compared to other major cereal crops (Fig. 1). Pearl millet plays an essential role in addressing food and nutritional security for rural and vulnerable populations residing in arid regions characterized by scant rainfall (Chivenge et al. 2015). The grains of pearl millet possess notable nutritional value, high levels of metabolizable energy, dietary fibers, proteins with a well-balanced amino acid profile, lipids, essential minerals, vitamins, and antioxidants (Ben Romdhane et al. 2023; Triki et al. 2022). The levels of iron (Fe) and zinc (Zn) in pearl millet seeds were reported to be higher than wheat, rice and maize (Srivastava et al. 2021). Furthermore, pearl millet finds wide application in the development of diverse value-added products. It is used as ingredients in food industry of nutritious snacks, bakery items, porridges, flatbreads, pasta, soups, sweets, as well as in the crafting of alcoholic and non-alcoholic beverages (Palak et al. 2023). Additionally, pearl millet is used to prepare Ready-to-Eat Flakes and Puffs, expanding its culinary versatility (Lokeswari and Mahendran 2022).
Pearl millet grain and pre-flowering vegetative parts assumes a crucial role as a valuable feed resource for livestock, especially in arid regions where feed scarcity exacerbates during the dry season. Pearl millet is well-suited for feeding various animal categories, encompassing ruminants like cattle and sheep, as well as monogastric creatures such as poultry and pigs. Moreover, beyond its grain, diverse by-products stemming from pearl millet processing, including straw and stover, emerge as valuable constituents of livestock feed (Umutoni et al. 2021). Its nutritional composition and adaptability render it an optimal choice for incorporation into animal feed formulations according to specific nutritional requirements (Cai et al. 2020).
Aside from its value as a source of sustenance for both humans and livestock, pearl millet serves as a gluten-free and nutritious cereal, particularly beneficial for crafting functional foods and beverages that contribute to human well-being. Notably, pearl millet has been integrated into multi-millet flour, utilized in the creation of nutritious products as an alternative to wheat flour, specifically for individuals with celiac disease and gastrointestinal concerns (Arepally et al. 2023). Scientific exploration has shed light on the diverse biological activities associated with pearl millet. Recent research has demonstrated that its phenolic compounds play a crucial role in inhibiting carbohydrate-digesting enzymes and regulating glucose transporters, implicating their potential in managing diabetes (Krishnan et al. 2022). The pro-apoptotic effects of pearl millet phenolic compounds on osteosarcoma U-2OS cells were also reported (Nani et al. 2019). A higher antioxidant property of pearl millet genotypes than wheat and maize was highlighted (Berwal et al. 2016). Pearl millet phenolics used as effective antioxidants have antiproliferative and DNA damage protection, helping in the regulation of carcinogenesis both at initiation and progression stages (Chandrasekara and Shahidi 2011; Salar and Purewal 2017), Table 1.
Table 1 . Biological activities of pearl millet
Biological activity | Used part | Extract fraction | References |
---|---|---|---|
Anti-diabetic effect | Grain | Phenolic extract | Krishnan et al. (2022) |
Protection against oxidative damage, anti-coagulant, anti-platelet activity | Grain | Protein extract | Shivaiah et al. (2023) |
Anti-oxidant, anti-proliferative, DNA scission inhibitory effects | Grain | Phenolic extract | Chandrasekara and Shahidi (2011) |
Pro-apoptotic effect against U-2OS osteosarcoma cells | Grain | Phenolic extract | Nani et al. (2019) |
Anti-oxidant | Grain | Phenolic extract | Berwal et al. (2016) |
Anti-diabetic, anti-lipidemic, and anti-oxidant effects | Flour | Protein hydrolysate | Mudgil et al. (2023) |
Anti-obesity, hypoglycemic, hypolipidemic, anti-inflammatory, anti-steatotic effects. | Grain | Grain powder | Alzahrani et al. (2022) |
Ethanol extract | |||
Anti-oxidant potential, DNA damage protection | Grain | Defatted ethanol extract | Salar and Purewal (2017) |
Pearl millet was used to produce multigrain porridge with superior nutritional quality; its consumption alleviates hyperglycemia, hypercholesterolemia and oxidative stress in obese-diabetic Wistar Rats (Olagunju 2022). Other study outlined the potential of pearl millet proteins as source for bioactive hydrolysates with improved anti-diabetic, anti-lipidemic, and anti-oxidant activities with potential as functional food ingredient (Mudgil et al. 2023). Both the raw powder and ethanolic extract of pearl millet have a dose-dependent anti-obesity, hypoglycemic, hypolipidemic, anti-inflammatory, and anti-steatotic activity in HFD-fed rats (Alzahrani et al. 2022). Furthermore, pearl millet protein extract have revealed its capacity to protect RBC, liver, kidney, and the small intestine from oxidative damage and also exhibited anticoagulant and antiplatelet activities (Shivaiah et al. 2023). Other report outlined the prebiotic potential of pearl millet’s oligosaccharides indicating their suitability for utilization as nutraceuticals and additives to functional food products (Mondal et al. 2022). Thus, low-calorie cake was developed by incorporating pearl millet maltodextrin (Syed et al. 2011). Others pearl millet-based food items, such as millet couscous and thick porridge were developed to promote satiety and to reduce glycemic response (Hayes et al. 2021), Fig. 2.
Pearl millet offers others non food industrial applications. This species is gaining significant interest as a bioenergy crop for the production of bioethanol and biogas due to its high biomass yield and adaptability to marginal lands (Laougé and Merdun 2020). The species is used in bone tissue engineering (Athinarayanan et al. 2019), as a source of cellulosic fluff (Yadav et al. 2019), for the production of biodegradable packaging material (Bangar et al. 2022) and as bio-coagulants for water treatment (Hussain and Haydar 2019). Moreover, a circular economy strategy to produce a fungal-based biopesticide using pearl millet as a substrate was reported (Chaparro et al. 2021). In some African areas, pearl millet landraces with high stover and tillers are used as construction material (Loumerem et al. 2008), Table 2.
Table 2 . Non-food industrial interests of pearl millet
Industrial use | Used part | References |
---|---|---|
Substrate for biopesticide production | Grain | Chaparro et al. (2021) |
Production of biodegradable packaging material | Pearl millet starch | Bangar et al. (2022) |
Bio-coagulant for water treatment | Grain | Hussain and Haydar (2019) |
Bioenergy | Residues | Laougé and Merdun (2020) |
Source of cellulosic fluff pulp | Pearl millet stalk | Yadav et al. (2019) |
Bone tissue engineering | Grain husk | Athinarayanan et al. (2019) |
Pearl millet is renowned for its robustness and ability to withstand harsh environmental stresses, including heat, limited water and nutrient availability, as well as reduced susceptibility to salinity in comparison to other major cereals and is then considered as a smart-climate cereal (Serba et al. 2020). However, grain yields are generally low, mainly because this crop is often cultivated for subsistence under extremely harsh conditions, in marginal soils, in areas of low rainfall and with little or no inputs. The ever-changing climate presents new challenges for this species and creates various types of ecological issues (Rhoné et al. 2020). Abiotic stress such as high temperatures, drought, salinity, and soil nutrient deficiencies, along with low temperatures in others areas, act as notable constraints, hampering both the optimal biomass and grain productivity and quality of pearl millet. Various abiotic stresses are major threats for its growth and development causing severe losses in its yield potential. Among these abiotic stresses, drought stress is the most devastating constraint that can occur at any growth stage in pearl millet causing yield losses of up to 55-67% (Tara Satyavathi et al. 2021). In particular, terminal drought induces reductions in various physiological, growth, and yield characteristics of pearl millet (Wasaya et al. 2022). Additionally, when subjected to salinity stress, pearl millet undergoes notable alterations in its physiological and biochemical processes, leading to adverse impacts on both its growth and productivity (Khan et al. 2023). Although this cereal crop is renowned for its inherent tolerance to heat stress, pearl millet exhibits increased susceptibility in the arid regions of Asia and Africa, which are more prone to rising temperatures (Pushpavalli et al. 2020). In certain cropping regions, the species faces a significant challenge to its growth during winter due to low temperatures (Alshoaibi 2022), Table 3.
Table 3 . Requirements for pearl millet improvement
Traits for pearl millet improvement | References | |
---|---|---|
Biotic threats | Downy mildew (Sclerospora graminicola) | Murria et al. (2022) |
Blast (Magnaporthe grisea) | Sharma et al. (2018) | |
Rust (Puccinia substriata var. indica) | Ambawat et al. (2016) | |
Ergot (Claviceps sp) | Murria et al. (2022) | |
Viral diseases (e.g., marafivirus and mosaic virus) | Palanga et al. (2022) | |
Weeds (Striga hermonthica) | Unachukwu et al. (2017) | |
Abiotic stresses | Heat | Pushpavalli et al. (2020) |
Low temperature | Alshoaibi (2022) | |
Drought | Wasaya et al. (2022) | |
Salinity | Khan et al. (2023) | |
Anti-nutritional traits | Phytates | Boncompagni et al. (2018) |
Tannins | Joshi and Rao (2024) | |
C-glycosylflavones | Boncompagni et al. (2018) | |
Oxalates | Kaur et al. (2023) | |
Insoluble fibers | Krishnan and Meera (2017) | |
Rancidity | Pallavi et al. (2023) |
Pearl millet confronts a range of biotic threats that impact its growth and yields. From pest invasions to microbial diseases, these challenges pose substantial risks to its cultivation and productivity. Phytopathogen threats caused by fungal, bacterial, and viral agents have detrimental impacts on pearl millet production (Chanwala et al. 2022). Fungal diseases such as Cercospora leaf spot, Bipolaris leaf spot, and the devastating downy mildew caused by Sclerospora graminicola, as well as ergot caused by Claviceps, reduce the crop’s productivity (Murria et al. 2022). The emergence of Blast due to Magnaporthe grisea poses a significant threat to forage pearl millet in India (Sharma et al. 2018). Sclerospora graminicola causes the most devastating disease of pearl millet and may lead to annual grain yield losses of up to ~80% and substantial deterioration of forage quality and production (Chelpuri et al. 2019). Rust, caused by the fungus Puccinia substriata var. indica, is one of the most significant biotic constraints for pearl millet worldwide, leading to grain yield losses of up to 76% as well as major losses in fodder yield and quality (Ambawat et al. 2016). The intensification of pearl millet cultivation has resulted in the emergence of viral diseases. Nevertheless, there is a lack of comprehensive documentation regarding current epidemiological data and the extent of yield losses attributed to these viruses (Palanga et al. 2022).
The invasion of weeds, especially during the initial years of rainy seasons, stands out as a primary hurdle for pearl millet. The detrimental impact of weeds on crop growth, yield, and overall farm profitability adds to the complexity of the agricultural faced challenges (Chinyo et al. 2023). Weeds pose a challenge to millet crops during their initial slow growth stage as they compete for various essential resources such as nutrients, soil moisture, light, and space. Striga hermonthica, a weedy plant that parasitizes pearl millet throughout Sub-Saharan Africa can have dramatic effects on its production (Unachukwu et al. 2017). Furthermore, this weed has been documented in India, posing a significant threat to the yields of pearl millet (Mahapatra et al. 2023), Table 3.
In spite of its commendable nutritional value, pearl millet has certain anti-nutritional characteristics that have the potential to hinder the absorption of vital nutrients and adversely affect human well-being. Notable anti-nutrients found in pearl millet grains include phytates, the goitrogenic compounds C-glycosylflavones (Boncompagni et al. 2018), tannins (Joshi and Rao 2024), oxalates (Kaur et al. 2023), insoluble fibers (Krishnan and Meera 2017) and iron-binding phenolic compounds (Boncompagni et al. 2018). A plethora of in vivo and in vitro studies have highlighted their detrimental effects on the bioavailability of essential elements such as iron, zinc, and other cations, potentially leading to reduced absorption (Kumar et al. 2022). Furthermore, undesired attributes like off-flavors and traits related to rancidity have been associated with pearl millet. The rancidity and browning of pearl millet flour during storage is the major limitation to consumer acceptance. Measures to alleviate these concerns in pearl millet have been pursued due to the presence of polyphenolic compounds and heightened lipase enzyme activity. These factors can trigger unfavorable changes in flavor and color in the final product, thereby limiting its acceptance in both traditional and modern food industry sectors (Pallavi et al. 2023; Pawase et al. 2019). Investigations have indicated significant variation in the levels of these anti-nutritional compounds within different genotypes of pearl millet (Boncompagni et al. 2018), Table 3.
The main genetic resources of pearl millet are constituted by landraces. The genetic diversity within pearl millet landraces is extensive, encompassing a broad spectrum of traits. Notably, landraces originating from West Africa exhibit characteristics such as delayed maturation, tall stature, robust stalks, short spikes, and substantial grain size. Conversely, in Western India, landraces tend to mature early, display slender stems, and exhibit prolific branching, resulting in staggered flowering events, which may serve as an adaptive strategy to cope with arid conditions (Chowdari et al. 1998). Additionally, the contemporary assortment of pearl millet germplasm comprises also enhanced elite materials, conventional cultivars, genetic stocks, and wild progenitors. A total of 56,580 accessions of pearl millet are conserved in 70 Gene Banks situated within 46 countries worldwide. The Indian national collection, situated at the National Bureau of Plant Genetic Resources (NBPGR) in New Delhi, houses 7,059 accessions. India, reported as the first main producer of pearl millet worldwide, gave a specific interest to this nutri-cereal. The National Bureau of Plant Genetic Resources (NBPGR) in New Delhi preserves 7,059 pearl millet accessions representing the Indian national collection (Yadav et al. 2017). On the other hand, 22,888 pearl millet accessions, 19,696 of them represent landraces, originated from 51 countries were conserved in the Gene Bank of the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) located in India which present the largest collection of pearl millet in the world (Upadhyaya et al. 2017).
Efforts were undertaken to allow further the utilization of these genetic resources to enhance the yields and quality of this crop. Thus, 22 traits were used to create a core collection of 2094 pearl millet accessions (Upadhyaya et al. 2009). Later a mini core-collection consists of 238 accessions was chosen (Upadhyaya et al. 2011). These valuable genetic resources have served as plant material for various investigations across the world which focused on unraveling the desirable traits within pearl millet. This includes improvements of grain nutritional traits, enhancing resistance to biotic threats, and the enhancement of resilience against abiotic stresses, particularly those posed by drought and heat (Govindaraj et al. 2020; Yadav et al. 2017). Various improved cultivars have been created to adapt to a spectrum of distinct growth conditions and to effectively address the specific nutritional demands of local populations (Kanfany et al. 2020).
The improvement of pearl millet is a continuous and significant challenge for plant biotechnologists and breeders. Efforts to improve pearl millet through conventional and modern breeding along with biotechnological strategies have been implemented to enhance its yield, nutritional quality, and resistance to various biotic and abiotic stresses. The genetic improvement of pearl millet has been carried out by developing hybrids through conventional breeding procedures mainly in India. Since 1962, more than 167 hybrids and 61 varieties have been developed and released in India and their number is expected to increase due to ever changing breeding objectives to meet the current and the future demands of producers and consumers. The cultivation of these hybrids extends to 70% of the total pearl millet area and resulted in an increase of 124% in the productivity of this nutricereal since 1986-90 (Tara Satyavathi et al. 2018).
Advancements in molecular markers technologies have revolutionized traditional improvement strategies of this orphan crop and played a significant role in its Indian modern breeding. Conventional breeding approaches based on crosses and phenotypic selection for desirable characteristics has been used to improve pearl millet (Govindaraj et al. 2019). However this method relies on the breeder’s expertise and can be subjective, time-consuming, and labor-intensive and does not capture the real genetic variations potential of the investigated germplasms (Rani et al. 2022). Furthermore, no significant success has been gained in case of abiotic stress tolerance due to multigenic nature and complex inheritance of these traits (Jangra et al. 2019). The integration of molecular biology into the modern breeding process allowed breeders to make more efficient decisions and facilitated the identification, selection, and tracking of specific genes or genomic regions associated with desired traits. They facilitate genetic diversity assessment, conservation efforts, and hybrid and seeds purity assessment and enabled the enhancement of genomic assisted selection (Ponnaiah et al. 2019).
The incorporation of pearl millet into African agriculture has been a longstanding and essential aspect of the region’s farming heritage, contributing significantly to the sustenance of communities over many generations. In contrast to the adoption of pearl millet hybrid cultivars by Indian farmers several decades ago, agricultural practices in Africa predominantly center on traditional landraces and open-pollinated varieties (Ben Romdhane et al. 2019; Riahi et al. 2021; Sattler and Haussmann 2020). The acceptance of hybrids and improved varieties in Africa remains low (Gaoh et al. 2023). This has led to consistently lower production yields for this species in African countries compared to those recorded in Asia, as evidenced by lower ratios of production (tons) to cultivated areas (ha) (Fig. 3). At the opposition of Indian breeding research strategies which emphasizes single-cross hybrids, efforts in Africa are more directed towards population hybrids (Sattler et al. 2019). Biotic and abiotic threats recorded for pearl millet, coupled with the cultivation of non-improved cultivars, have resulted in the absence of any increase in millet production (in tons) compared to major cereals such as wheat, maize, and rice over the last decade (FAOSTAT 2024), Fig. 4.
While pearl millet possesses numerous commendable attributes, continuous improvement is imperative to fully unlock its potential. Research efforts should focus on breeding programs which aim to enhance yields, nutritional contents, and resilience to emerging environmental challenges. Developing varieties with improved post-harvest traits and mechanized harvesting options can further streamline the crop’s integration into modern agricultural systems. Despite its potential significance to global agriculture, genomic assisted breeding of pearl millet has received limited attention. This crop remains largely underexplored and undervalued. The main hindrances to realizing pearl millet’s full production potential are low hybrid adoption, slow varietal diffusion, and disease susceptibility. These challenges can be mitigated by diversifying male-sterile lines, improving restorers, and developing diverse heterozygous hybrids to address both low yields and disease susceptibility.
The importance of preserving and harnessing the genetic diversity within pearl millet’s genetic resources is both comprehensive and crucial for achieving adaptation to changing environments, nutritional enhancement, and disease resistance. Local pearl millet landraces are still growing in contrasting agro-ecological environments and are considered potentially useful for national and international breeders for useful genes of interest. These landraces hold significant economic and cultural importance as representing the natural genetic diversity of pearl millet that has evolved over centuries. Their genetic diversity presents a reservoir of new genes to develop climate-resilient varieties with enhanced yields, nutritional contents, and overall crop performance. Conservation and research efforts are crucial to safeguard these genetic resources and to fully exploit their potential for sustainable agriculture and food security.
The authors are thankful to the Tunisian Ministry of Higher Education and Scientific Research for financial support.
J Plant Biotechnol 2024; 51(1): 77-88
Published online April 9, 2024 https://doi.org/10.5010/JPB.2024.51.009.077
Copyright © The Korean Society of Plant Biotechnology.
Leila Riahi ・Mériam Ben-Romdhane ・Ahmed S. Masmoudi
Laboratory of Biotechnology and Bio-Geo Resources Valorization BVBGR-LR11ES31, ISBST, University of Manouba, 2020 Sidi Thabet, Ariana, Tunisia
Laboratory of Plant Molecular Physiology, Centre of Biotechnology of Borj Cedria, 2050 Hammam-Lif, Tunisia
Correspondence to:e-mail: leila.ba.riahi@gmail.com
This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Pearl millet is a small-seeded staple crop in arid and semi-arid regions of Africa and Asia. It is the crop of choice in the hottest and driest climates where other cereals do not grow well and is considered a future climate-smart cereal. This underutilized cereal provides nutritional and food security to millions of people. It is also used as animal feed, fuel, and fodder as well as in brewing. The gluten-free grains of this cereal are rich sources of fats, proteins, carbohydrates, minerals, especially iron and zinc, and phenolics with health-promoting properties. Pearl millet also has industrial uses in the production of bioenergy, biodegradable products, bio-coagulants, and construction materials, and in tissue engineering. Pearl millet hybrids have gained considerable popularity among Indian farmers, resulting in a significant increase in production yields. However, pearl millet production in Africa is primarily dependent on traditional landraces with limited acceptance of improved open-pollinated varieties and hybrids. Consequently, no significant increase in pearl millet production has been achieved over the past few decades. Despite its inherent resilience against poor climates, this staple crop faces a complex array of abiotic and biotic stresses in its production areas, which is exacerbated by ongoing climate change. Furthermore, certain anti-nutritional traits impede its overall nutritional value and effective utilization. Hence, improving pearl millet is a continuous and significant challenge for plant breeders and biotechnologists.
Keywords: Pearl millet, Gluten free, Smart cereal, Improvement, Climate change
Pearl millet (Pennisetum glaucum (L.) R.Br. syn. Cenchrus americanus (L.) Morrone) assumes a crucial role as a staple nutri-cereal crop in arid and semi-arid regions of Africa and Asia. Moreover, pearl millet is gaining prominence as forage and cover crop in countries such as Canada, the United States, Mexico, Central Asia, Brazil and Australia (Singh and Nara 2023). Globally, it is the sixth most important cereal crop in the world behind maize, rice, wheat, barley and sorghum and addresses the dietary requirements and socio-economic well-being of millions (Satyavathi et al. 2021). Pearl millet is acknowledged for its elevated nutritional and caloric characteristics which promoted its high potential as food, feed and forage. It serves as a primary dietary component, especially in developing nations, owing to its substantial levels of carbohydrates, proteins, fats, vitamins, and essential minerals, notably iron and zinc. Additionally, pearl millet is gaining popularity as functional foods throughout the world (Samtiya et al. 2023). Notably, this cereal is abundant in bioactive compounds with significant health-promoting potential, including phenolic acids, flavonoids, and dietary fiber (Triki et al. 2022). Pearl millet also exhibits significant potential as industrial crop with increasing interests in bioenergy production, textile engineering and the production of eco-friendly biodegradable products (Ben Romdhane et al. 2022).
Pearl millet stands out as one of the most heat-tolerant and resilient cultivated cereals, displaying remarkable drought, salinity and low soil fertility tolerance and has historically acted as a reliable source of sustenance in areas experiencing unpredictable climate patterns (Meena et al. 2020). It holds
significant importance as a major food crop for smallholder subsistence farmers residing in the semi-arid tropical regions of Africa and Asia (Pucher et al. 2016). This under-utilized crop, have superior resilience to drought and heat stress than wheat and is considered a model crop for abiotic stress tolerance studies (Ghatak et al. 2021). Its drought tolerance, rapid growth, and low-input requirements have positioned it as a lifeline for smallholder farmers against food insecurity and poverty in arid ecosystems and make of it a climate-smart cereal with substantial potential in the future in the context of the ongoing climatic changes (Hassan et al. 2021).
Despite pearl millet’s remarkable resilience to abiotic stresses and its substantial nutritional value, the imperative for its improvement remains an ongoing challenge. Indeed, on-farm pearl millet yields tend to be consistently low, exhibiting significant variability even within the same farm (Diallo et al. 2019). Moreover, pearl millet is susceptible to diverse biotic stresses, including weeds along with fungal, viral, and bacterial infections (Chanwala et al. 2022). Therefore, the enhancement of pearl millet’s tolerance to both abiotic and biotic stress, the biofortification of its nutrient profiles, and the resolution of prevailing constraints that hinder its full potential can further enhance the significance of pearl millet as a nutri-cereal and industrial crop with diversified products and uses. This will secure its ongoing role in bolstering food security within arid regions; characterized by new and increasingly challenging environments, as well as an unprecedented population increase.
Pearl millet (Pennisetum glaucum (L.) R.Br. syn. Cenchrus americanus (L.) Morrone) represents an annual C4 and diploid (2n = 2x = 14) cereal belonging to the Poaceae family. This crop has a relatively small genome with DNA content of 1C = 2.36 pg (Martel et al. 1997). This robust and rapidly growing annual grass exhibits substantial morphological diversity, typically ranging from 1 to 3 meters in height, although it can attain heights up to 5 meters (Upadhyaya et al. 2008). Pearl millet is a highly cross-pollinated crop characterized by protogynous flowering. Traditional cultivars of this species form random-mating populations marked by considerable levels of heterozygosity and heterogeneity. Pollination primarily occurs through wind and insects, particularly by bees (Serba et al. 2019).
Pearl millet, traceable through archaeological records, stands as the most ancient African cereal and is intimately linked with the appearance of agriculture in West Africa (Burgarella et al. 2018). The domestication trajectory of pearl millet finds its origins over 4,000 years ago within the Sahel region of West Africa from its wild progenitor, Pennisetum violaceum (Lam.) Rich. [syn. P. americanum subsp. monodii (Maire) Brunken]. Later, this crop was expanded to East Africa and India (Fuller et al. 2021). The centre of origin and diversification is accepted to be within West Africa, where a persistent gene flow with its wild ancestor persists (Sattler and Haussmann 2020). Archaeological evidence highlighted the presence of fully cultivated pearl millet in Southeastern Mali by the second half of the third millennium BC and in eastern Sudan by the early second millennium BC (Winchell et al. 2018). The last authors reported that the dispersal of pearl millet to India took less than 1000 years. Later, the cultivation of this crop spread to various parts of the globe, including South Asia, Eastern and Southern Africa, facilitated by maritime trades. In approximately the 8th Century, the introduction of this cereal reached North African countries (Tostain 1998). Actually, pearl millet is mainly cultivated in Africa and India as staple cereal crop but also cropped in USA, Latin America, Canada and Australia as forage and cover crop (Sharma et al. 2021).
Pearl millet serves as a versatile cereal crop cultivated for various purposes, including grain, green fodder and stover. The species ranks sixth worldwide in terms of cultivation extent, after wheat, maize, rice, barley, and sorghum. It is a major staple crop for 90 million poor people and is cultivated on 27 million ha area in arid and semi-arid tropics of Asia and Africa. Interestingly, its significance is even more pronounced in African country and India. Pearl millet is one of the most important crops in the whole Sahelian region from Senegal to Sudan (Mariac et al. 2006). This crop ranks second in Senegal (Bastos et al. 2022) and fourth in Benin (Adeoti et al. 2017). In Niger, pearl millet covers more than 65% of the total cultivated area (Mariac et al. 2006). This crop stands as a dietary staple for over 70% of Namibia’s population (McBenedict et al. 2016) and is the most important summer crop in Southern Tunisia (Loumerem et al. 2008). In Sudan, 74% of dietary energy is derived from pearl millet (Boncompagni et al. 2018). In India, pearl millet is the third most widely cultivated food crop after rice and wheat (Kumar et al. 2020). Across arid and semiarid territories in Africa and Southern Asia, pearl millet plays a pivotal role in traditional farming systems and as a primary food source. Additionally, it finds utility as a temporary summer pasture or cover crop in the Americas and Australia (Serba et al. 2019).
Due to its remarkable photosynthetic efficiency and capacity for dry-matter production, pearl millet emerges as a preferred crop for farmers in challenging agroclimatic zones, where other cereals are likely to fail to produce economic yields (Satyavathi et al. 2021). This crop has a relatively short growth cycle which facilitates the practice of double cropping in many regions. Moreover, pearl millet has lower minimal optimal rainfall and higher maximal optimal temperatures compared to other major cereal crops (Fig. 1). Pearl millet plays an essential role in addressing food and nutritional security for rural and vulnerable populations residing in arid regions characterized by scant rainfall (Chivenge et al. 2015). The grains of pearl millet possess notable nutritional value, high levels of metabolizable energy, dietary fibers, proteins with a well-balanced amino acid profile, lipids, essential minerals, vitamins, and antioxidants (Ben Romdhane et al. 2023; Triki et al. 2022). The levels of iron (Fe) and zinc (Zn) in pearl millet seeds were reported to be higher than wheat, rice and maize (Srivastava et al. 2021). Furthermore, pearl millet finds wide application in the development of diverse value-added products. It is used as ingredients in food industry of nutritious snacks, bakery items, porridges, flatbreads, pasta, soups, sweets, as well as in the crafting of alcoholic and non-alcoholic beverages (Palak et al. 2023). Additionally, pearl millet is used to prepare Ready-to-Eat Flakes and Puffs, expanding its culinary versatility (Lokeswari and Mahendran 2022).
Pearl millet grain and pre-flowering vegetative parts assumes a crucial role as a valuable feed resource for livestock, especially in arid regions where feed scarcity exacerbates during the dry season. Pearl millet is well-suited for feeding various animal categories, encompassing ruminants like cattle and sheep, as well as monogastric creatures such as poultry and pigs. Moreover, beyond its grain, diverse by-products stemming from pearl millet processing, including straw and stover, emerge as valuable constituents of livestock feed (Umutoni et al. 2021). Its nutritional composition and adaptability render it an optimal choice for incorporation into animal feed formulations according to specific nutritional requirements (Cai et al. 2020).
Aside from its value as a source of sustenance for both humans and livestock, pearl millet serves as a gluten-free and nutritious cereal, particularly beneficial for crafting functional foods and beverages that contribute to human well-being. Notably, pearl millet has been integrated into multi-millet flour, utilized in the creation of nutritious products as an alternative to wheat flour, specifically for individuals with celiac disease and gastrointestinal concerns (Arepally et al. 2023). Scientific exploration has shed light on the diverse biological activities associated with pearl millet. Recent research has demonstrated that its phenolic compounds play a crucial role in inhibiting carbohydrate-digesting enzymes and regulating glucose transporters, implicating their potential in managing diabetes (Krishnan et al. 2022). The pro-apoptotic effects of pearl millet phenolic compounds on osteosarcoma U-2OS cells were also reported (Nani et al. 2019). A higher antioxidant property of pearl millet genotypes than wheat and maize was highlighted (Berwal et al. 2016). Pearl millet phenolics used as effective antioxidants have antiproliferative and DNA damage protection, helping in the regulation of carcinogenesis both at initiation and progression stages (Chandrasekara and Shahidi 2011; Salar and Purewal 2017), Table 1.
Table 1 . Biological activities of pearl millet.
Biological activity | Used part | Extract fraction | References |
---|---|---|---|
Anti-diabetic effect | Grain | Phenolic extract | Krishnan et al. (2022) |
Protection against oxidative damage, anti-coagulant, anti-platelet activity | Grain | Protein extract | Shivaiah et al. (2023) |
Anti-oxidant, anti-proliferative, DNA scission inhibitory effects | Grain | Phenolic extract | Chandrasekara and Shahidi (2011) |
Pro-apoptotic effect against U-2OS osteosarcoma cells | Grain | Phenolic extract | Nani et al. (2019) |
Anti-oxidant | Grain | Phenolic extract | Berwal et al. (2016) |
Anti-diabetic, anti-lipidemic, and anti-oxidant effects | Flour | Protein hydrolysate | Mudgil et al. (2023) |
Anti-obesity, hypoglycemic, hypolipidemic, anti-inflammatory, anti-steatotic effects. | Grain | Grain powder | Alzahrani et al. (2022) |
Ethanol extract | |||
Anti-oxidant potential, DNA damage protection | Grain | Defatted ethanol extract | Salar and Purewal (2017) |
Pearl millet was used to produce multigrain porridge with superior nutritional quality; its consumption alleviates hyperglycemia, hypercholesterolemia and oxidative stress in obese-diabetic Wistar Rats (Olagunju 2022). Other study outlined the potential of pearl millet proteins as source for bioactive hydrolysates with improved anti-diabetic, anti-lipidemic, and anti-oxidant activities with potential as functional food ingredient (Mudgil et al. 2023). Both the raw powder and ethanolic extract of pearl millet have a dose-dependent anti-obesity, hypoglycemic, hypolipidemic, anti-inflammatory, and anti-steatotic activity in HFD-fed rats (Alzahrani et al. 2022). Furthermore, pearl millet protein extract have revealed its capacity to protect RBC, liver, kidney, and the small intestine from oxidative damage and also exhibited anticoagulant and antiplatelet activities (Shivaiah et al. 2023). Other report outlined the prebiotic potential of pearl millet’s oligosaccharides indicating their suitability for utilization as nutraceuticals and additives to functional food products (Mondal et al. 2022). Thus, low-calorie cake was developed by incorporating pearl millet maltodextrin (Syed et al. 2011). Others pearl millet-based food items, such as millet couscous and thick porridge were developed to promote satiety and to reduce glycemic response (Hayes et al. 2021), Fig. 2.
Pearl millet offers others non food industrial applications. This species is gaining significant interest as a bioenergy crop for the production of bioethanol and biogas due to its high biomass yield and adaptability to marginal lands (Laougé and Merdun 2020). The species is used in bone tissue engineering (Athinarayanan et al. 2019), as a source of cellulosic fluff (Yadav et al. 2019), for the production of biodegradable packaging material (Bangar et al. 2022) and as bio-coagulants for water treatment (Hussain and Haydar 2019). Moreover, a circular economy strategy to produce a fungal-based biopesticide using pearl millet as a substrate was reported (Chaparro et al. 2021). In some African areas, pearl millet landraces with high stover and tillers are used as construction material (Loumerem et al. 2008), Table 2.
Table 2 . Non-food industrial interests of pearl millet.
Industrial use | Used part | References |
---|---|---|
Substrate for biopesticide production | Grain | Chaparro et al. (2021) |
Production of biodegradable packaging material | Pearl millet starch | Bangar et al. (2022) |
Bio-coagulant for water treatment | Grain | Hussain and Haydar (2019) |
Bioenergy | Residues | Laougé and Merdun (2020) |
Source of cellulosic fluff pulp | Pearl millet stalk | Yadav et al. (2019) |
Bone tissue engineering | Grain husk | Athinarayanan et al. (2019) |
Pearl millet is renowned for its robustness and ability to withstand harsh environmental stresses, including heat, limited water and nutrient availability, as well as reduced susceptibility to salinity in comparison to other major cereals and is then considered as a smart-climate cereal (Serba et al. 2020). However, grain yields are generally low, mainly because this crop is often cultivated for subsistence under extremely harsh conditions, in marginal soils, in areas of low rainfall and with little or no inputs. The ever-changing climate presents new challenges for this species and creates various types of ecological issues (Rhoné et al. 2020). Abiotic stress such as high temperatures, drought, salinity, and soil nutrient deficiencies, along with low temperatures in others areas, act as notable constraints, hampering both the optimal biomass and grain productivity and quality of pearl millet. Various abiotic stresses are major threats for its growth and development causing severe losses in its yield potential. Among these abiotic stresses, drought stress is the most devastating constraint that can occur at any growth stage in pearl millet causing yield losses of up to 55-67% (Tara Satyavathi et al. 2021). In particular, terminal drought induces reductions in various physiological, growth, and yield characteristics of pearl millet (Wasaya et al. 2022). Additionally, when subjected to salinity stress, pearl millet undergoes notable alterations in its physiological and biochemical processes, leading to adverse impacts on both its growth and productivity (Khan et al. 2023). Although this cereal crop is renowned for its inherent tolerance to heat stress, pearl millet exhibits increased susceptibility in the arid regions of Asia and Africa, which are more prone to rising temperatures (Pushpavalli et al. 2020). In certain cropping regions, the species faces a significant challenge to its growth during winter due to low temperatures (Alshoaibi 2022), Table 3.
Table 3 . Requirements for pearl millet improvement.
Traits for pearl millet improvement | References | |
---|---|---|
Biotic threats | Downy mildew (Sclerospora graminicola) | Murria et al. (2022) |
Blast (Magnaporthe grisea) | Sharma et al. (2018) | |
Rust (Puccinia substriata var. indica) | Ambawat et al. (2016) | |
Ergot (Claviceps sp) | Murria et al. (2022) | |
Viral diseases (e.g., marafivirus and mosaic virus) | Palanga et al. (2022) | |
Weeds (Striga hermonthica) | Unachukwu et al. (2017) | |
Abiotic stresses | Heat | Pushpavalli et al. (2020) |
Low temperature | Alshoaibi (2022) | |
Drought | Wasaya et al. (2022) | |
Salinity | Khan et al. (2023) | |
Anti-nutritional traits | Phytates | Boncompagni et al. (2018) |
Tannins | Joshi and Rao (2024) | |
C-glycosylflavones | Boncompagni et al. (2018) | |
Oxalates | Kaur et al. (2023) | |
Insoluble fibers | Krishnan and Meera (2017) | |
Rancidity | Pallavi et al. (2023) |
Pearl millet confronts a range of biotic threats that impact its growth and yields. From pest invasions to microbial diseases, these challenges pose substantial risks to its cultivation and productivity. Phytopathogen threats caused by fungal, bacterial, and viral agents have detrimental impacts on pearl millet production (Chanwala et al. 2022). Fungal diseases such as Cercospora leaf spot, Bipolaris leaf spot, and the devastating downy mildew caused by Sclerospora graminicola, as well as ergot caused by Claviceps, reduce the crop’s productivity (Murria et al. 2022). The emergence of Blast due to Magnaporthe grisea poses a significant threat to forage pearl millet in India (Sharma et al. 2018). Sclerospora graminicola causes the most devastating disease of pearl millet and may lead to annual grain yield losses of up to ~80% and substantial deterioration of forage quality and production (Chelpuri et al. 2019). Rust, caused by the fungus Puccinia substriata var. indica, is one of the most significant biotic constraints for pearl millet worldwide, leading to grain yield losses of up to 76% as well as major losses in fodder yield and quality (Ambawat et al. 2016). The intensification of pearl millet cultivation has resulted in the emergence of viral diseases. Nevertheless, there is a lack of comprehensive documentation regarding current epidemiological data and the extent of yield losses attributed to these viruses (Palanga et al. 2022).
The invasion of weeds, especially during the initial years of rainy seasons, stands out as a primary hurdle for pearl millet. The detrimental impact of weeds on crop growth, yield, and overall farm profitability adds to the complexity of the agricultural faced challenges (Chinyo et al. 2023). Weeds pose a challenge to millet crops during their initial slow growth stage as they compete for various essential resources such as nutrients, soil moisture, light, and space. Striga hermonthica, a weedy plant that parasitizes pearl millet throughout Sub-Saharan Africa can have dramatic effects on its production (Unachukwu et al. 2017). Furthermore, this weed has been documented in India, posing a significant threat to the yields of pearl millet (Mahapatra et al. 2023), Table 3.
In spite of its commendable nutritional value, pearl millet has certain anti-nutritional characteristics that have the potential to hinder the absorption of vital nutrients and adversely affect human well-being. Notable anti-nutrients found in pearl millet grains include phytates, the goitrogenic compounds C-glycosylflavones (Boncompagni et al. 2018), tannins (Joshi and Rao 2024), oxalates (Kaur et al. 2023), insoluble fibers (Krishnan and Meera 2017) and iron-binding phenolic compounds (Boncompagni et al. 2018). A plethora of in vivo and in vitro studies have highlighted their detrimental effects on the bioavailability of essential elements such as iron, zinc, and other cations, potentially leading to reduced absorption (Kumar et al. 2022). Furthermore, undesired attributes like off-flavors and traits related to rancidity have been associated with pearl millet. The rancidity and browning of pearl millet flour during storage is the major limitation to consumer acceptance. Measures to alleviate these concerns in pearl millet have been pursued due to the presence of polyphenolic compounds and heightened lipase enzyme activity. These factors can trigger unfavorable changes in flavor and color in the final product, thereby limiting its acceptance in both traditional and modern food industry sectors (Pallavi et al. 2023; Pawase et al. 2019). Investigations have indicated significant variation in the levels of these anti-nutritional compounds within different genotypes of pearl millet (Boncompagni et al. 2018), Table 3.
The main genetic resources of pearl millet are constituted by landraces. The genetic diversity within pearl millet landraces is extensive, encompassing a broad spectrum of traits. Notably, landraces originating from West Africa exhibit characteristics such as delayed maturation, tall stature, robust stalks, short spikes, and substantial grain size. Conversely, in Western India, landraces tend to mature early, display slender stems, and exhibit prolific branching, resulting in staggered flowering events, which may serve as an adaptive strategy to cope with arid conditions (Chowdari et al. 1998). Additionally, the contemporary assortment of pearl millet germplasm comprises also enhanced elite materials, conventional cultivars, genetic stocks, and wild progenitors. A total of 56,580 accessions of pearl millet are conserved in 70 Gene Banks situated within 46 countries worldwide. The Indian national collection, situated at the National Bureau of Plant Genetic Resources (NBPGR) in New Delhi, houses 7,059 accessions. India, reported as the first main producer of pearl millet worldwide, gave a specific interest to this nutri-cereal. The National Bureau of Plant Genetic Resources (NBPGR) in New Delhi preserves 7,059 pearl millet accessions representing the Indian national collection (Yadav et al. 2017). On the other hand, 22,888 pearl millet accessions, 19,696 of them represent landraces, originated from 51 countries were conserved in the Gene Bank of the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) located in India which present the largest collection of pearl millet in the world (Upadhyaya et al. 2017).
Efforts were undertaken to allow further the utilization of these genetic resources to enhance the yields and quality of this crop. Thus, 22 traits were used to create a core collection of 2094 pearl millet accessions (Upadhyaya et al. 2009). Later a mini core-collection consists of 238 accessions was chosen (Upadhyaya et al. 2011). These valuable genetic resources have served as plant material for various investigations across the world which focused on unraveling the desirable traits within pearl millet. This includes improvements of grain nutritional traits, enhancing resistance to biotic threats, and the enhancement of resilience against abiotic stresses, particularly those posed by drought and heat (Govindaraj et al. 2020; Yadav et al. 2017). Various improved cultivars have been created to adapt to a spectrum of distinct growth conditions and to effectively address the specific nutritional demands of local populations (Kanfany et al. 2020).
The improvement of pearl millet is a continuous and significant challenge for plant biotechnologists and breeders. Efforts to improve pearl millet through conventional and modern breeding along with biotechnological strategies have been implemented to enhance its yield, nutritional quality, and resistance to various biotic and abiotic stresses. The genetic improvement of pearl millet has been carried out by developing hybrids through conventional breeding procedures mainly in India. Since 1962, more than 167 hybrids and 61 varieties have been developed and released in India and their number is expected to increase due to ever changing breeding objectives to meet the current and the future demands of producers and consumers. The cultivation of these hybrids extends to 70% of the total pearl millet area and resulted in an increase of 124% in the productivity of this nutricereal since 1986-90 (Tara Satyavathi et al. 2018).
Advancements in molecular markers technologies have revolutionized traditional improvement strategies of this orphan crop and played a significant role in its Indian modern breeding. Conventional breeding approaches based on crosses and phenotypic selection for desirable characteristics has been used to improve pearl millet (Govindaraj et al. 2019). However this method relies on the breeder’s expertise and can be subjective, time-consuming, and labor-intensive and does not capture the real genetic variations potential of the investigated germplasms (Rani et al. 2022). Furthermore, no significant success has been gained in case of abiotic stress tolerance due to multigenic nature and complex inheritance of these traits (Jangra et al. 2019). The integration of molecular biology into the modern breeding process allowed breeders to make more efficient decisions and facilitated the identification, selection, and tracking of specific genes or genomic regions associated with desired traits. They facilitate genetic diversity assessment, conservation efforts, and hybrid and seeds purity assessment and enabled the enhancement of genomic assisted selection (Ponnaiah et al. 2019).
The incorporation of pearl millet into African agriculture has been a longstanding and essential aspect of the region’s farming heritage, contributing significantly to the sustenance of communities over many generations. In contrast to the adoption of pearl millet hybrid cultivars by Indian farmers several decades ago, agricultural practices in Africa predominantly center on traditional landraces and open-pollinated varieties (Ben Romdhane et al. 2019; Riahi et al. 2021; Sattler and Haussmann 2020). The acceptance of hybrids and improved varieties in Africa remains low (Gaoh et al. 2023). This has led to consistently lower production yields for this species in African countries compared to those recorded in Asia, as evidenced by lower ratios of production (tons) to cultivated areas (ha) (Fig. 3). At the opposition of Indian breeding research strategies which emphasizes single-cross hybrids, efforts in Africa are more directed towards population hybrids (Sattler et al. 2019). Biotic and abiotic threats recorded for pearl millet, coupled with the cultivation of non-improved cultivars, have resulted in the absence of any increase in millet production (in tons) compared to major cereals such as wheat, maize, and rice over the last decade (FAOSTAT 2024), Fig. 4.
While pearl millet possesses numerous commendable attributes, continuous improvement is imperative to fully unlock its potential. Research efforts should focus on breeding programs which aim to enhance yields, nutritional contents, and resilience to emerging environmental challenges. Developing varieties with improved post-harvest traits and mechanized harvesting options can further streamline the crop’s integration into modern agricultural systems. Despite its potential significance to global agriculture, genomic assisted breeding of pearl millet has received limited attention. This crop remains largely underexplored and undervalued. The main hindrances to realizing pearl millet’s full production potential are low hybrid adoption, slow varietal diffusion, and disease susceptibility. These challenges can be mitigated by diversifying male-sterile lines, improving restorers, and developing diverse heterozygous hybrids to address both low yields and disease susceptibility.
The importance of preserving and harnessing the genetic diversity within pearl millet’s genetic resources is both comprehensive and crucial for achieving adaptation to changing environments, nutritional enhancement, and disease resistance. Local pearl millet landraces are still growing in contrasting agro-ecological environments and are considered potentially useful for national and international breeders for useful genes of interest. These landraces hold significant economic and cultural importance as representing the natural genetic diversity of pearl millet that has evolved over centuries. Their genetic diversity presents a reservoir of new genes to develop climate-resilient varieties with enhanced yields, nutritional contents, and overall crop performance. Conservation and research efforts are crucial to safeguard these genetic resources and to fully exploit their potential for sustainable agriculture and food security.
The authors are thankful to the Tunisian Ministry of Higher Education and Scientific Research for financial support.
Table 1 . Biological activities of pearl millet.
Biological activity | Used part | Extract fraction | References |
---|---|---|---|
Anti-diabetic effect | Grain | Phenolic extract | Krishnan et al. (2022) |
Protection against oxidative damage, anti-coagulant, anti-platelet activity | Grain | Protein extract | Shivaiah et al. (2023) |
Anti-oxidant, anti-proliferative, DNA scission inhibitory effects | Grain | Phenolic extract | Chandrasekara and Shahidi (2011) |
Pro-apoptotic effect against U-2OS osteosarcoma cells | Grain | Phenolic extract | Nani et al. (2019) |
Anti-oxidant | Grain | Phenolic extract | Berwal et al. (2016) |
Anti-diabetic, anti-lipidemic, and anti-oxidant effects | Flour | Protein hydrolysate | Mudgil et al. (2023) |
Anti-obesity, hypoglycemic, hypolipidemic, anti-inflammatory, anti-steatotic effects. | Grain | Grain powder | Alzahrani et al. (2022) |
Ethanol extract | |||
Anti-oxidant potential, DNA damage protection | Grain | Defatted ethanol extract | Salar and Purewal (2017) |
Table 2 . Non-food industrial interests of pearl millet.
Industrial use | Used part | References |
---|---|---|
Substrate for biopesticide production | Grain | Chaparro et al. (2021) |
Production of biodegradable packaging material | Pearl millet starch | Bangar et al. (2022) |
Bio-coagulant for water treatment | Grain | Hussain and Haydar (2019) |
Bioenergy | Residues | Laougé and Merdun (2020) |
Source of cellulosic fluff pulp | Pearl millet stalk | Yadav et al. (2019) |
Bone tissue engineering | Grain husk | Athinarayanan et al. (2019) |
Table 3 . Requirements for pearl millet improvement.
Traits for pearl millet improvement | References | |
---|---|---|
Biotic threats | Downy mildew (Sclerospora graminicola) | Murria et al. (2022) |
Blast (Magnaporthe grisea) | Sharma et al. (2018) | |
Rust (Puccinia substriata var. indica) | Ambawat et al. (2016) | |
Ergot (Claviceps sp) | Murria et al. (2022) | |
Viral diseases (e.g., marafivirus and mosaic virus) | Palanga et al. (2022) | |
Weeds (Striga hermonthica) | Unachukwu et al. (2017) | |
Abiotic stresses | Heat | Pushpavalli et al. (2020) |
Low temperature | Alshoaibi (2022) | |
Drought | Wasaya et al. (2022) | |
Salinity | Khan et al. (2023) | |
Anti-nutritional traits | Phytates | Boncompagni et al. (2018) |
Tannins | Joshi and Rao (2024) | |
C-glycosylflavones | Boncompagni et al. (2018) | |
Oxalates | Kaur et al. (2023) | |
Insoluble fibers | Krishnan and Meera (2017) | |
Rancidity | Pallavi et al. (2023) |
Kenneth Happy ・ Roggers Gang ・ Yeongjun Ban ・ Sungyu Yang ・ Endang Rahmat ・ Denis Okello ・ Richard Komakech ・ Okello Cyrus ・ Kalule Okello David ・ Youngmin Kang
J Plant Biotechnol 2024; 51(1): 167-201
Journal of
Plant Biotechnology