Cowpea [Vigna unguiculata (L.) Walp.] is a diploid and nutrient-dense legume species. It provides affordable source of protein to human. Cowpea cultivation is prevalent in Africa, Asia, the western and southern U.S., and Central and South America. However, earlier reports have shown that drought and salt stress can be devastating to cowpea production. The objectives of this study were to screen for salt and drought tolerance in cowpea and to identify molecular markers associated with these traits. Simple methodologies to screen for drought (Chapter 2) and salt tolerance were developed (Chapter 3). Results suggested that: 1) a total of 14, 18, 5, 5, and 35 SNPs were associated with plant growth habit change due to drought stress, drought tolerance index for maturity, flowering time, 100-seed weight, and grain yield respectively in a MAGIC cowpea population, the network-guided approach revealed clear interactions between the loci associated with the drought tolerance traits, and GS accuracy varied from low to moderate for this population, 2) a total of 7, 2, 18, 18, 3, 2, 5, 1, and 23 SNPs were associated with various traits evaluated for salt tolerance in a MAGIC cowpea population, some of these SNPs were in the vicinity of potassium channel and biomolecule transporters, and significant epistatic interactions were found 3) a large variation of salt tolerance and drought tolerance was found in the panel involving 331 cowpea genotypes which were genotyped with 14,465,516 SNPs obtained from whole-genome resequencing, 4) tolerance to salt and drought-related traits seemed to be associated with the geographical origins of the cowpea genotypes, 5) a significant GWAS peak defined by a cluster of 196 significant SNPs and mapped on a 210-kb region of chromosome 5 was identified to be a good locus candidate for tolerance to trifoliate leaf chlorosis under drought stress in cowpea and harbored hormone-induced genes, and 6) a strong candidate locus for tolerance to leaf score injury under salt stress and defined by a cluster of 1,400 significant SNPs on chromosome 3 was identified and this region harbored a potassium channel gene. The results from this study could contribute to a better understanding of salt and drought tolerance in cowpea. The salt- and drought-tolerant genotypes could be used as parents in cowpea breeding programs.

The book provides a reader with relevant information on Cowpea research and in particular the genetics of grain and vegetative biomass yields under well-watered and drought stress conditions during the vegetative phase of cowpea, establishing the yield penalty associated with vegetative-stage drought in cowpea in the parental lines and their F1 hybrids, in relation to hybrid vigour for drought tolerance and to identify the cowpea genotype with the highest tolerance to vegetative-stage drought among a set of nine genotypes reputed for drought tolerance. The book is relevant for Lecturers, Students, Researchers in the field of Crop Sciences and in particular Plant Breeding and Genetics. For readers who are interested in the use of molecular biology tools for crop improvement, genetic basis of the physiological mechanisms adapting field crops to stress factors, genotype x environment interaction in crop plants, methodologies in field crop improvement, multi-environment evaluation of field crops, field trial methodology, student training etc, this is a book of relevance and you should not miss it.

In the wake of rising temperatures, erratic rainfall, and declining ground water table, breeding for drought tolerance in food crops has become a top priority throughout the world. Phenotyping a large population of breeding lines for drought tolerance is time-consuming and often unreliable due to multiple possible mechanisms involved. In cowpea (Vigna unguiculata L. Walp), a box-screening method has been used to partition the confounding effects that shoot and root traits have on drought tolerance by restricting root growth and providing a homogeneous soil moisture environment across genotypes. Nonetheless, multiple mechanisms of shoot drought tolerance have been reported which further complicate phenotyping. In winter wheat (Triticum aestivum L.), canopy temperature depression (CTD) has been proposed as a good indicator of drought tolerance. The recent development of low-cost thermal imaging devices could enable high-throughput phenotyping of canopy temperature. While CTD can be an indicator of overall plant water status, it can be confounded by high stomatal resistance, which is another seemingly contradictory mechanism of drought tolerance. The objectives of this study were to explore the physiological basis and genetics of the two mechanisms of shoot drought tolerance previously reported in cowpea and to develop and evaluate a method of high-throughput phenotyping of drought tolerance in winter wheat using thermal imaging. In cowpea, a legume well known for its tight stomatal control, no differences in gas exchange between drought tolerant and susceptible genotypes were observed. A unifoliate stay-green trait was discovered that segregates as a single recessive gene. However, it did not correlate with trifoliate necrosis or overall drought tolerance. In winter wheat, CTD did not always correlate with yield under rainfed conditions. One drought-tolerant cultivar, in particular, had the hottest canopy temperature, possibly because it was able to conserve moisture by closing its stomata whereas another closely related drought-tolerant cultivar had the coolest canopy temperature. Therefore, it appears that no single method of phenotyping for drought tolerance can be broadly applied across all genotypes of a given species due to possible contrasting mechanisms of drought-tolerance and environmental differences. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/152439

This book deliberates on the concept, strategies, tools, and techniques of allele mining in grain legume crops and its application potential in genome elucidation and improvement, including studying allele evolution, discovery of superior alleles, discerning new haplotypes, assessment of intra- and interspecific similarity, and also studies of gene expression and gene prediction. Available gene pools in global germplasm collections specifically consisting of wild allied species and local landraces for almost all major crops have facilitated allele mining. Development of advanced genomic techniques, including PCR-based allele priming and EcoTILLING-based allele mining, is being widely used now for mining superior alleles. Allele's discovery has become more relevant now for employing molecular breeding to develop designed crop varieties matching consumer needs, and also with genome plasticity to adapt to climate change scenarios. All these concepts and strategies, along with precise success stories, are presented in the chapters dedicated to the major grain legume crops. 1. The first book on the novel strategy of allele mining in grain legume crops for precise breeding. 2. Presents genomic strategies for mining superior alleles underlying agronomic traits from genomic resources. 3. Depicts case studies of PCR-based allele priming and EcoTILLING-based allele mining. 4. Elaborates on gene discovery and gene prediction in major grain legume crops. This book will be useful to students and faculties in various plant science disciplines, including genetics, genomics, molecular breeding, agronomy, and bioinformatics; to scientists in seed industries; and also to policymakers and funding agencies interested in crop improvement.

This book presents deliberations on molecular and genomic mechanisms underlying the interactions of crop plants to the abiotic stresses caused by heat, cold, drought, flooding, submergence, salinity, acidity, etc., important to develop resistant crop varieties. Knowledge on the advanced genetic and genomic crop improvement strategies including molecular breeding, transgenics, genomic-assisted breeding, and the recently emerging genome editing for developing resistant varieties in pulse crops is imperative for addressing FHNEE (food, health, nutrition, energy, and environment) security. Whole genome sequencing of these crops followed by genotyping-by-sequencing has provided precise information regarding the genes conferring resistance useful for gene discovery, allele mining, and shuttle breeding which in turn opened up the scope for 'designing' crop genomes with resistance to abiotic stresses. The nine chapters each dedicated to a pulse crop in this volume elucidate on different types of abiotic stresses and their effects on and interaction with the crop; enumerate on the available genetic diversity with regard to abiotic stress resistance among available cultivars; illuminate on the potential gene pools for utilization in interspecific gene transfer; present brief on classical genetics of stress resistance and traditional breeding for transferring them to their cultivated counterparts; depict the success stories of genetic engineering for developing abiotic stress-resistant crop varieties; discuss on molecular mapping of genes and QTLs underlying stress resistance and their marker-assisted introgression into elite varieties; enunciate on different genomics-aided techniques including genomic selection, allele mining, gene discovery, and gene pyramiding for developing adaptive crop varieties with higher quantity and quality of yields, and also elaborate some case studies on genome editing focusing on specific genes for generating abiotic stress-resistant crops.