Pearl millet is one of the most important small-grained C4 Panicoid crops with a large genome size (~2352 Mb), short life cycle and outbreeding nature. It is highly resilient to areas with scanty rain and high temperature. Pearl millet is a nutritionally superior staple crop for people inhabiting hot, drought-prone arid and semi-arid regions of South Asia and Africa where it is widely grown and used for food, hay, silage, bird feed, building material and fuel. Having excellent nutrient composition and exceptional buffering capacity against variable climatic conditions and pathogen attack makes pearl millet a wonderful model crop for stress tolerance studies. Pearl millet germplasm show a large range of genotypic and phenotypic variations including tolerance to abiotic and biotic stresses. Conventional breeding for enhancing abiotic and biotic stress resistance in pearl millet have met with considerable success, however in last few years various novel approaches including functional genomics and molecular breeding have been attempted in this crop for augmenting yield under adverse environmental conditions, and there is still a lot of scope for further improvement using genomic tools. Discovery and use of various DNA-based markers such as EST-SSRs, DArT, CISP, and SSCP-SNP in pearl millet not only help in determining population structure and genetic diversity but also prove to be important for developing strategies for crop improvement at a faster rate and greater precision. Molecular marker-based genetic linkage maps and identification of genomic regions determining yield under abiotic stresses particularly terminal drought have paved way for marker-assisted selection and breeding of pearl millet cultivars. Reference collections and marker-assisted backcrossing have also been used to improve biotic stress resistance in pearl millet specifically to downy mildew. Whole genome sequencing of pearl millet genome will give new insights for processing of functional genes and assist in crop improvement programs through molecular breeding approaches. This review thus summarizes the exploration of pearl millet genetic and genomic resources for improving abiotic and biotic stress resistance and development of cultivars superior in stress tolerance.

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Exploration of Genetic and Genomic Resources for Abiotic and Biotic Stress Tolerance in Pearl Millet

Rising global temperatures due to climate change are affecting crop performance in several regions of the world. High temperatures affect plants at various organizational levels, primarily accelerating phenology to limit biomass production and shortening reproductive phase to curtail flower and fruit numbers, thus resulting in severe yield losses. Besides, heat stress also disrupts normal growth, development, cellular metabolism, and gene expression, which alters shoot and root structures, branching patterns, leaf surface and orientation, and anatomical, structural, and functional aspects of leaves and flowers. The reproductive growth stage is crucial in plants' life cycle, and susceptible to high temperatures, as reproductive processes are negatively impacted thus reducing crop yield. Genetic variation exists among genotypes of various crops to resist impacts of heat stress. Several screening studies have successfully phenotyped large populations of various crops to distinguish heat-tolerant and heat-sensitive genotypes using various traits, related to shoots (including leaves), flowers, fruits (pods, spikes, spikelets), and seeds (or grains), which have led to direct release of heat-tolerant cultivars in some cases (such as chickpea). In the present review, we discuss examples of contrasting genotypes for heat tolerance in different crops, involving many traits related to thermotolerance in leaves (membrane thermostability, photosynthetic efficiency, chlorophyll content, chlorophyll fluorescence, stomatal activity), flowers (pollen viability, pollen germination, fertilization, ovule viability), roots (architecture), biomolecules (antioxidants, osmolytes, phytohormones, heat-shock proteins, other stress proteins), and "omics" (phenomics, transcriptomics, genomics) approaches. The traits linked to heat tolerance can be introgressed into high yielding but heat-sensitive genotypes of crops to enhance their thermotolerance. Involving these traits will be useful for screening contrasting genotypes and would pave the way for characterizing the underlying molecular mechanisms, which could be valuable for engineering plants with enhanced thermotolerance. Wherever possible, we discussed breeding and biotechnological approaches for using these traits to develop heat-tolerant genotypes of various food crops.

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Identification and Characterization of Contrasting Genotypes/Cultivars for Developing Heat Tolerance in Agricultural Crops: Current Status and Prospects.

Recognizing production options for pearl millet in Pakistan under changing climate scenarios

Many farmers in West and Central Africa (WCA) prefer tall (>3 m) grain sorghum [Sorghum bicolor (L.) Moench] for various reasons. This study seeks to determine (i) what yield superiority newly bred, tall, photoperiod-sensitive guinea-race sorghum hybrids can provide relative to an adapted landrace variety across a wide range of productivity conditions, and (ii) the risk of these hybrids failing to provide yield superiority for individual farmers. Seven hybrids, one local check, and eight pure-line progenies were evaluated in 37 farmer-managed, on-farm yield trials across three Malian zones and 3 yr. Environments were classified into four productivity groups (low [0.78–1.10 Mg ha−1], mid-low [1.10–1.50 Mg ha−1], mid-high [1.50–2.00 Mg ha−1] and high [2.00–2.65 Mg ha−1]) based on their trial mean grain yield. Mean yields of the seven tall hybrids were 3 to 17% (ranging from 0.06 to 0.28 Mg ha−1) higher than that of the local check across all environments and were highest (14–47%) averaged across the seven trials with the lowest mean yields. The individual overall highest-yielding hybrid showed superiorities over the local check in the low, mid-low, mid-high, and high productivity levels of 0.43 (47%), 0.14 (10%), 0.47 (27%), and 0.34 (14%) Mg ha−1, respectively. The tall hybrids rarely had yields significantly inferior to the local check. Farmers’ preference for, and the possible benefits of, taller plant types may lead farmers to grow tall hybrids, particularly under the typical low-productivity production conditions of WCA.

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Can Tall Guinea-Race Sorghum Hybrids Deliver Yield Advantage to Smallholder Farmers in West and Central Africa?

Drought and heat in dryland agriculture challenge the enhancement of crop productivity and threaten global food security. This review is centered on harnessing genetic variation through biotechnology-led approaches to select for increased productivity and stress tolerance that will enhance crop adaptation in dryland environments. Peer-reviewed literature, mostly from the last decade and involving experiments with at least two seasons' data, form the basis of this review. It begins by highlighting the adverse impact of the increasing intensity and duration of drought and heat stress due to global warming on crop productivity and its impact on food and nutritional security in dryland environments. This is followed by (1) an overview of the physiological and molecular basis of plant adaptation to elevated CO2 (eCO2), drought, and heat stress; (2) the critical role of high-throughput phenotyping platforms to study phenomes and genomes to increase breeding efficiency; (3) opportunities to enhance stress tolerance and productivity in food crops (cereals and grain legumes) by deploying biotechnology-led approaches [pyramiding quantitative trait loci (QTL), genomic selection, marker-assisted recurrent selection, epigenetic variation, genome editing, and transgene) and inducing flowering independent of environmental clues to match the length of growing season; (4) opportunities to increase productivity in C3 crops by harnessing novel variations (genes and network) in crops' (C3, C4) germplasm pools associated with increased photosynthesis; and (5) the adoption, impact, risk assessment, and enabling policy environments to scale up the adoption of seed-technology to enhance food and nutritional security. This synthesis of technological innovations and insights in seed-based technology offers crop genetic enhancers further opportunities to increase crop productivity in dryland environments.

Using Biotechnology-Led Approaches to Uplift Cereal and Food Legume Yields in Dryland Environments.

Utilization of agricultural waste biomass and recycling toward circular bioeconomy

Ten pearl millet genotypes selected on the basis of response to supra-optimal temperature tolerance were crossed in a half-diallel mating system. The 45 hybrids produced were tested along with parents for heat tolerance and related traits at seedling stage. Field screening and laboratory screening techniques were simultaneously used for the evaluation of hybrids and their parents. Heat tolerance was measured as seedling thermotolerance index (STI) and seed to seedling thermotolerance index (SSTI) under field conditions, but membrane thermostability (MTS) in the laboratory. The hybrid H77/29-2 CVJ-2-5-3-1-3 showed highest STI value followed by H77/833-2 96AC-93. The genotype H77/833-2 96AC-93 had the highest worth for SSTI. These three indices were highly correlated among themselves. STI values were invariably high, whereas SSTI has lower values, as it also covers the effect of under soil mortality (USM). It was seen that the heat tolerance indices STI and SSTI were not showing any perceptible pooled correlation with developmental traits except germination and emergence rate. Based on our results, it could be suggested that membrane thermostability (MTS) may be used for screening large number of genotypes. Field based indices STI and SSTI may be used for evaluation of hybrids and varieties before they are released.

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Screening of Pearl Millet F1 Hybrids for Heat Tolerance at Early Seedling Stage

Genetic control of temperature tolerance was investigated in pearl millet at seedling stage. Ten parents were selected through a field screening technique. They were crossed in a diallel manner. Fortyfive F1 hybrids along with their 10 parents were tested for performance in randomized block design with three replications under supra-optimal temperature exposure at seedling stage. The experiment was conducted in three environments at different dates of sowing from May to July 2005. The Griffings method of diallel analysis was used to obtain the genetic estimates. Variances due to general combining ability and specific combining ability for all the characters studied, viz seedling thermo-tolerance index, seed to seedling thermo-tolerance index, germination, emergence rate, leaves/seedling, seedling height, seedling fresh weight, seedling dry weight were highly significant in all the three environments (two stress and one normal) indicating the importance of both additive and non-additive genetic variances. The non-additive (dominance) component was more prominent for all the characters. It suggested that heterosis breeding could be successful. The genotype ‘CVJ 2-5- 3-1-3’ and ‘(77/371×BSECT CP 1)’ were identified as the best general combiners for both the heat tolerance indices. Seven hybrds, namely, ‘H77/833-2×96AC-93’, ‘1305×96AC-93’, ‘(77/371×BSECT CP-1)×Togo II’, ‘H77/29-2×CVJ 2-5-3-1-3’, ‘1305×99HS-18’, ‘G73 107×77/245’ and ‘H77/833-2×H77/29-2’ were identified having high values of heat tolerance indices seedling thermo-tolerance index and seed to seedling thermo-tolerance index. The estimates of additive genetic variance and narrow sense heritability for seedling thermo-tolerance index and seed to seedling thermo-tolerance index were high.

Genetic dissection of temperature tolerance in pearl millet ( Pennisetum glaucum)

Pearl millet [Pennisetum glaucum (L.) R. Br. emend Stanz] is a coarse grain crop hospitable to millions of people and animals over the world and grown under most inhospitable conditions of environment. The crop is more important for India and Africa where it is a means of livelihood of human and cattle population providing food, feed and fodder. Globally, it is cultivated over an area of about 26 million hectares. Rajasthan accounts for more than 50 per cent cultivation of the country’s 9 million ha including desert areas. Importance of the crop thus assumes a central place in poor resource farmer agriculture and animal husbandry dominated

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Multivariate analysis of pearl millet data to delineate genetic variation

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Rajesh Kumar Arya

Papers

Utilization of agricultural waste biomass and recycling toward circular bioeconomy

Screening of Pearl Millet F1 Hybrids for Heat Tolerance at Early Seedling Stage

Genetic dissection of temperature tolerance in pearl millet ( Pennisetum glaucum)

Multivariate analysis of pearl millet data to delineate genetic variation

Study of Genetic Architecture for Maturity Traits in Relation to Supra-optimal Temperature Tolerance in Pearl Millet (Pennisetum glaucum (L.) R.Br.)