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Small millets are nutrient-rich food sources traditionally grown and consumed by subsistence farmers in Asia and Africa. They include finger millet (Eleusine coracana), foxtail millet (Setaria italica), kodo millet (Paspalum scrobiculatum), proso millet (Panicum miliaceum), barnyard millet (Echinochloa spp.), and little millet (Panicum sumatrense). Local farmers value the small millets for their nutritional and health benefits, tolerance to extreme stress including drought, and ability to grow under low nutrient input conditions, ideal in an era of climate change and steadily depleting natural resources. Little scientific attention has been paid to these crops, hence they have been termed \"orphan cereals.\" Despite this challenge, an advantageous quality of the small millets is that they continue to be grown in remote regions of the world which has preserved their biodiversity, providing breeders with unique alleles for crop improvement. The purpose of this review, first, is to highlight the diverse traits of each small millet species that are valued by farmers and consumers which hold potential for selection, improvement or mechanistic study. For each species, the germplasm, genetic and genomic resources available will then be described as potential tools to exploit this biodiversity. The review will conclude with noting current trends and gaps in the literature and make recommendations on how to better preserve and utilize diversity within these species to accelerate a New Green Revolution for subsistence farmers in Asia and Africa.

A germplasm assembly of 128 finger millet genotypes from 18 countries was evaluated for seedling-stage phosphorus (P) responses by growing them in P sufficient (Psuf) and P deficient (Pdef) treatments. Majority of the genotypes showed adaptive responses to low P condition. Based on phenotype behaviour using the best linear unbiased predictors for each trait, genotypes were classified into, P responsive, low P tolerant and P non-responsive types. Based on the overall phenotype performance under Pdef, 10 genotypes were identified as low P tolerants. The low P tolerant genotypes were characterised by increased shoot and root length and increased root hair induction with longer root hairs under Pdef, than under Psuf. Association mapping of P response traits using mixed linear models revealed four quantitative trait loci (QTLs). Two QTLs (qLRDW.1 and qLRDW.2) for low P response affecting root dry weight explained over 10% phenotypic variation. In silico synteny analysis across grass genomes for these QTLs identified putative candidate genes such as Ser-Thr kinase and transcription factors such as WRKY and basic helix-loop-helix (bHLH). The QTLs for response under Psuf were mapped for traits such as shoot dry weight (qHSDW.1) and root length (qHRL.1). Putative associations of these QTLs over the syntenous regions on the grass genomes revealed proximity to cytochrome P450, phosphate transporter and pectin methylesterase inhibitor (PMEI) genes. This is the first report of the extent of phenotypic variability for P response in finger millet genotypes during seedling-stage, along with the QTLs and putative candidate genes associated with P starvation tolerance.

Main conclusionMillets’ protein studies are lagging behind those of major cereals. Current status and future insights into the investigation of millet proteins are discussed.Millets are important small-seeded cereals majorly grown and consumed by people in Asia and Africa and are considered crops of future food security. Although millets possess excellent climate resilience and nutrient supplementation properties, their research advancements have been lagging behind major cereals. Although considerable genomic resources have been developed in recent years, research on millet proteins and proteomes is currently limited, highlighting a need for further investigation in this area. This review provides the current status of protein research in millets and provides insights to understand protein responses for climate resilience and nutrient supplementation in millets. The reference proteome data is available for sorghum, foxtail millet, and proso millet to date; other millets, such as pearl millet, finger millet, barnyard millet, kodo millet, tef, and browntop millet, do not have any reference proteome data. Many studies were reported on stress-responsive protein identification in foxtail millet, with most studies on the identification of proteins under drought-stress conditions. Pearl millet has a few reports on protein identification under drought and saline stress. Finger millet is the only other millet to have a report on stress-responsive (drought) protein identification in the leaf. For protein localization studies, foxtail millet has a few reports. Sorghum has the highest number of 40 experimentally proven crystal structures, and other millets have fewer or no experimentally proven structures. Further proteomics studies will help dissect the specific proteins involved in climate resilience and nutrient supplementation and aid in breeding better crops to conserve food security.

Worldwide, millets are regarded as a significant grain, however, they are the least exploited. Millet grain is abundant in nutrients and health-beneficial phenolic compounds, making it suitable as food and feed. The diverse content of nutrients and phenolic compounds present in finger and pearl millet are good indicators that the variety of millet available is important when selecting it for use as food or feed. The phenolic properties found in millets compromise phenolic acids, flavonoids, and tannins, which are beneficial to human health. Moreover, finger millet has an exceptionally unique, more abundant, and diverse phenolic profile compared to pearl millet. Research has shown that millet phenolic properties have high antioxidant activity. The presence of phytochemicals in millet grains has positive effect on human health by lowering the cholesterol and phytates in the body. The frantic demands on maize and its uses in multiple industries have merited the search for alternative grains, to ease the pressure. Substitution of maize with pearl and finger millets in the diets of different animals resulted in positive impact on the performance. Including these grains in the diet may improve health and decrease the risks of diseases. Pearl millet of 50% or more can be used in broiler diets without adversely affecting broiler performance or egg production. Of late, millet grain has been incorporated in other foods and used to make traditional beverages. Thus, the core aim of this review is to provide insight and comprehension about the nutritional and phenolic status of millets and their impact on human and livestock.

Millets are nutrient-rich cereals majorly cultivated in Asia and Africa. Foxtail millet (FoxM), pearl millet (PeaM), finger millet (FinM), kodo millet (KodM), little millet (LitM), proso millet (ProM), and barnyard millet (BarM) were examined for the influence of external phosphorous (P) supply on phenotypic traits, P uptake, yield, and PHosphate Transporter1 (PHT1) family gene expression. Millet seedlings grown under low Pi condition (LPC) produced significantly lower mean values for all traits except for lateral root length (LRL) and lateral root number (LRN) which were increased under LPC. Under LPC, seed weight (SW) also reduced by > 75% and had significantly lower levels of total P (TP) and Pi contents in leaf and root tissues. Expression dynamics of 12 PHT1 family (PHT1; 1–1; 12) transporters genes were analyzed in 7 millets. PHT1; 2 has been found to be a constitutive transporter gene in all millets. Under LPC, root tissues showed the overexpression of PHT1; 2, 1; 3, 1; 4 and 1; 9 in FoxM, PHT1; 1, 1; 2, 1; 3, 1; 4, 1; 8 and 1; 10 in PeaM, PHT1; 2 and 1; 3 in FinM and ProM and PHT1; 3, 1; 6 and 1; 11 in BarM. In leaf, LPC induced the expression of PHT1; 3, 1; 4 and 1; 6 in FoxM, PHT1; 2, 1; 3, 1; 4 and 1; 8 in PeaM, PHT1; 2, 1; 3 and 1; 4 in FinM and KodM, PHT1; 2 in LitM and PHT1; 4 in ProM and BarnM. This comprehensive study on the influence of P in phenotype, physiology, and molecular responses may help to improve the P uptake and its use efficiency of millets in future.

Abstract Millets are small, seeded crops classified as major (pearl, finger, sorghum) or minor (proso, barnyard, foxtail, kodo, little) millet. Stating them as nutri-cereals, they deliver significant amounts of diverse nutrients that promote health as well as bioactive substances like antioxidants, dietary fiber, macro and micronutrients, and so on, when compared to other grains that are commonly consumed viz. rice, maize and wheat. These nutrients have an important role in the nutritious safekeeping of mankind. They are associated with numerous advantages, including drought tolerance, high yielding in limited water conditions, and they have high nutritious value. A comparative review was conducted among all the millets found in India. Here, the study on the application of processing techniques gives an insight into how nutritional values alter when the millets are being processed, and there is limited research on the loss of nutrients while processing as well as how the shelf-life or storage ability is affected. The easy cultivation process, resilient nature and high nutritional contents of these millets show a new area of research in current scenario of harsher climatic conditions. The purpose of this work is to review different types of millets, their nutritional composition and the effects of different processing methods on nutritional qualities. Resumo O milheto é uma pequena cultura com sementes, classificada como milheto principal (pérola, dedo, sorgo) ou secundário (proso, terreiro, rabo-de-raposa, kodo, pequeno). Denominados nutricereais, eles fornecem quantidades significativas de diversos nutrientes que promovem a saúde, bem como substâncias bioativas, como antioxidantes, fibra alimentar, macro e micronutrientes, entre outros, quando comparados a outros grãos comumente consumidos, como arroz, milho e trigo. Esses nutrientes desempenham um papel importante na proteção nutricional da humanidade. Estão associados a inúmeras vantagens, incluindo tolerância à seca, alto rendimento em condições de água limitada e alto valor nutritivo. Uma revisão comparativa foi realizada entre todos os milhetos encontrados na Índia. Aqui, o estudo sobre a aplicação de técnicas de processamento dá uma ideia de como os valores nutricionais se alteram quando os milhetos são processados. Note-se que há pesquisas limitadas sobre a perda de nutrientes durante o processamento, bem como se o prazo de validade ou a capacidade de armazenamento são afetados. O fácil processo de cultivo, a natureza resiliente e o alto teor nutricional desses milhetos mostram uma nova área de pesquisa no cenário atual de condições climáticas mais adversas. O objetivo deste trabalho é analisar diferentes tipos de milheto, sua composição nutricional e os efeitos de diferentes métodos de processamento nas qualidades nutricionais.

This study was conducted to understand the variation in the nutrient contents of different types of millets by collecting data from published scientific journals and collating it by variety. The data is analyzed as a whole and as a subset, where it is clearly categorized into a released variety or genotype/accession. Calcium level was consistently high in finger millet and teff regardless of varieties at 331.29 ± 10 mg/100 g and 183.41 ± 29 mg/100 g, respectively. Iron content was highest for finger millet at 12.21 ± 13.69 mg/100 g followed by teff at 11.09 ± 8.35 mg/100 g. Pearl millet contained the highest zinc content of 8.73 ± 11.55 mg/100 g. Protein content was highest in job’s tears at 12.66 g/100 g followed by proso millet at 12.42 ± 1.99 g/100 g and barnyard millet with 12.05 ± 1.77 g/100 g. Some millets showed consistently low or consistently high levels of specific nutrients, while others had such wide variation that they could not be characterized as high or low for that particular nutrient. There is a huge variation in the nutrient content of each type of millet regardless of the released variety or genotype. In the interest of improving dietary nutrients, there is a need to have nutrition programs and product development based on selected high nutrient varieties of the millet, which requires attention from researchers and government and changes in research, policy, and awareness among the public and private sectors.

Wild and weedy relatives of domesticated crops harbor genetic variants that can advance agricultural biotechnology. Here we provide a genome resource for the wild plant green millet ( Setaria viridis ), a model species for studies of C 4 grasses, and use the resource to probe domestication genes in the close crop relative foxtail millet ( Setaria italica ). We produced a platinum-quality genome assembly of S. viridis and de novo assemblies for 598 wild accessions and exploited these assemblies to identify loci underlying three traits: response to climate, a ‘loss of shattering’ trait that permits mechanical harvest and leaf angle, a predictor of yield in many grass crops. With CRISPR–Cas9 genome editing, we validated Less Shattering1 ( SvLes1 ) as a gene whose product controls seed shattering. In S. italica , this gene was rendered nonfunctional by a retrotransposon insertion in the domesticated loss-of-shattering allele SiLes1-TE (transposable element). This resource will enhance the utility of S. viridis for dissection of complex traits and biotechnological improvement of panicoid crops. Sequencing wild relatives of millet identifies genes that regulate yield and harvesting traits.

Achieving food security goals in West Africa will depend on the capacity of the agricultural sector to feed the rapidly growing population and to moderate the adverse impacts of climate change. Indeed, a number of studies anticipate a reduction of the crop yield of the main staple food crops in the region in the coming decades due to global warming. Here, we found that crop production might have already been affected by climate change, with significant yield losses estimated in the historical past. We used a large ensemble of historical climate simulations derived from an atmospheric general circulation model and two process-based crop models, SARRA-H and CYGMA, to evaluate the effects of historical climate change on crop production in West Africa. We generated two ensembles of 100 historical simulations of yields of sorghum and millet corresponding to two climate conditions for each crop model. One ensemble is based on a realistic simulation of the actual climate, while the other is based on a climate simulation that does not account for human influences on climate systems (that is, the non-warming counterfactual climate condition). We found that the last simulated decade, 2000–2009, is approximately 1 °C warmer in West Africa in the ensemble accounting for human influences on climate, with more frequent heat and rainfall extremes. These altered climate conditions have led to regional average yield reductions of 10–20% for millet and 5–15% for sorghum in the two crop models. We found that the average annual production losses across West Africa in 2000–2009 associated with historical climate change, relative to a non-warming counterfactual condition (that is, pre-industrial climate), accounted for 2.33–4.02 billion USD for millet and 0.73–2.17 billion USD for sorghum. The estimates of production losses presented here can be a basis for the loss and damage associated with climate change to date and useful in estimating the costs of the adaptation of crop production systems in the region.

Main conclusionThe review discusses growth and drought-response mechanisms in minor millets under three themes: drought escape, drought avoidance and drought tolerance.Drought is one of the most prominent abiotic stresses impacting plant growth, performance, and productivity. In the context of climate change, the prevalence and severity of drought is expected to increase in many agricultural regions worldwide. Millets (coarse grains) are a group of small-seeded grasses cultivated in arid and semi-arid regions throughout the world and are an important source of food and feed for humans and livestock. Although minor millets, i.e., foxtail millet, finger millet, proso millet, barnyard millet, kodo millet and little millet are generally hardier and more drought-resistant than cereals and major millets (sorghum and pearl millet), understanding their responses, processes and strategies in response to drought is more limited. Here, we review drought resistance strategies in minor millets under three themes: drought escape (e.g., short crop cycle, short vegetative period, developmental plasticity and remobilization of assimilates), drought avoidance (e.g., root traits for better water absorption and leaf traits to control water loss), and drought tolerance (e.g., osmotic adjustment, maintenance of photosynthetic ability and antioxidant potential). Data from ‘omics’ studies are summarized to provide an overview of the molecular mechanisms important in drought tolerance. In addition, the final section highlights knowledge gaps and challenges to improving minor millets. This review is intended to enhance major cereals and millet per se in light of climate-related increases in aridity.