Genetic And Genomic Resources Of Grain Legume Improvement

Grain legumes, including common-bean, chickpea, pigeonpea, pea, cowpea, lentil and others, form important constituents of global diets, both vegetarian and non-vegetarian. Despite this significant role, global production has increased only marginally in the past 50 years. The slow production growth, along with a rising human population and improved buying capacity has substantially reduced the per capita availability of food legumes. Changes in environmental climate have also had significant impact on production, creating a need to identify stable donors among genetic resources for environmentally robust genes and designing crops resilient to climate change. Genetic and Genomic Resources of Grain Legume Improvement is the first book to bring together the latest resources in plant genetics and genomics to facilitate the identification of specific germplasm, trait mapping and allele mining to more effectively develop biotic and abiotic-stress-resistant grains. This book will be an invaluable resource for researchers, crop biologists and students working with crop development. Explores origin, distribution and diversity of grain legumes Presents information on germplasm collection, evaluation and maintenance Offers insight into pre-breeding/germplasm enhancement efforts Integrates genomic and genetic resources in crop improvement Internationally contributed work

Pea is an important temperate region pulse, with feed, fodder and vegetable uses. It originated and was domesticated in Middle East and Mediterranean regions, and formed important dietary components of early civilizations. Although Pisum is a very small genus with two or three species, it is diverse and structured, reflecting taxonomy, ecogeography and breeding gene pools. This diversity has been preserved in collections totalling about 90,000 accessions. Core collections have been formed, facilitating phenotypic and agronomic evaluations. However, only 3% of ex situ collections are wild Pisum sp., with substantially larger diversity. The genomic resources allow initiation of association mapping, linking genetic diversity with trait manifestation. So far, only a small part of wild gene pools have been exploited in breeding for biotic and abiotic stresses. Current genomic knowledge and technologies can facilitate allele mining for novel traits and incorporation from wild Pisum sp. into elite domestic genetic backgrounds.

In this chapter, we lead the reader through several topics related to common bean germplasm, including crop dissemination across the Old World, landraces developed by farmers, characterization and safeguard of germplasm. These topics are attracting a great deal of attention, especially in recent years, when the international community has become increasingly aware of the relevance of safeguarding plant genetic resources. Early studies were mainly aimed at performing exploratory analyses of agro-morphological traits, with the goal of improving yield and pest resistance. Moreover, phaseolin variation was studied to check the distribution of the two common bean gene pools. The recent development of DNA-based markers has allowed significant improvement in knowledge on genetic variation within the European germplasm, as well as the capacity to trace its divergence from the American germplasm. The different strategies applied to safeguard the European germplasm are described together with their drawbacks.

Lentil (Lens culinaris spp. culinaris) has a long history associated with the early civilizations 11,000 BP in southwestern Asia. The progenitor taxon is Lens culinaris spp. orientalis. The primary source of germplasm for lentil crop improvement is from the International Center for Agricultural Research in the Dry Areas (ICARDA), Aleppo, Syria, and other ex situ national collections. Typical of many crop species, lentil experienced a genetic bottleneck during domestication. Fortunately, many biotic and abiotic stress resistances have been identified and accessed from the wild Lens taxon held ex situ to expand the genetic diversity available for crop improvement. Lentil crop wild relatives (CWR) represent

Grass pea (Lathyrus sativus L.) is an important cool-season legume species with wide genetic diversity spread across the continents. With the climate change scenario it has emerged as a viable crop option for fragile agro-ecosystems, where successful cultivation of major crop species is apparently not difficult. However, grass pea seeds are known to have a neurotoxin known as β-N-oxalyl-l-α, β-diaminopropionic acid (β-ODAP). Its overconsumption as a staple food in an unbalanced diet for an extended period of 3–4 months can cause spastic paraparesis of the legs in human beings. Therefore, β-ODAP needs to be reduced through genetic means to a safe level for human consumption. Unfortunately, a paucity of efforts towards development of genetic and genomic resources for this species has hampered the progress in breeding low ODAP varieties in the past. Some progress has been made in recent years for collection, conservation, characterization, evaluation and utilization of Lathyrus genetic resources at the national and international levels, resulting in large ex situ collections in various gene banks of the world. These resources need to be systematically characterized and evaluated for genetic improvement through conventional and contemporary approaches. In spite of a large number of wild relatives with useful traits, no significant efforts have been made for alien gene transfer in grass pea. This chapter reviews the present status of genetic and genomic resources of Lathyrus and their use in current breeding programmes.

Faba bean was first domesticated in the Near East about 10,000 BC. It is now grown worldwide on 2.56 million ha with a yield of 4.56 million tons. The traditional landraces are affected by the different biotic and abiotic stresses. Replacement of these low-yielding landraces by improved cultivars has resulted in a yield increase of 15.4kg/ha/year over the last 40 years. A reduction of the planted area from 7.5 million ha in 1961 to 2.56 million ha in 2010 and cultivation of improved cultivars are the major causes of genetic erosion. Gene banks around the world conserved more than 36,000 accessions. Diversity studies showed limited variation among currently grown cultivars, but high variation among different botanical groups has been recorded. The International Center for Agricultural Research in the Dry Areas has undertaken desirable selection and breeding efforts to identify different sources of resistance and to develop improved varieties in collaboration with national agricultural research systems. A molecular approach was used in advanced research institutes to tag major genes/quantitative trait loci with molecular markers. However, more efforts are needed to saturate the genetic maps to facilitate marker-assisted breeding.

Chickpea is an important protein-rich crop with considerable diversity present among 44 annual Cicer species. A large collection of chickpea germplasm including wild Cicer species has been conserved in different gene banks globally. However, the effective and efficient utilization of these resources is required to develop new cultivars with a broad genetic base. Using core and mini-core collections, chickpea researchers have identified diverse germplasm possessing various beneficial traits that are now being used in chickpea breeding. Further, for chickpea improvement, the genus Cicer harbours alleles/genes for tolerance/resistance to various abiotic and biotic stresses as well as for agronomic and nutrition-related traits. Recent advances in plant biotechnology have resulted in developing large number of markers specific to chickpea in addition to technological breakthrough in developing high-throughput genotyping platforms for unlocking the genetic potential available in germplasm collections.

Cowpea (Vigna unguiculata), an indigenous legume to sub-Saharan Africa, is mainly grown in the dry savanna areas as an intercrop with millets, sorghum, groundnut and maize. Cowpea grains rich in protein are consumed in different forms in several parts of the tropics. The average grain yield of cowpea in West Africa is approximately 492kg/ha, which is much lower than its potential yields. This low productivity is due to a host of diseases, insects, pests, parasitic weeds, drought, poor soils and low plant population density in farmers’ fields. Ex situ collection of over 15,000 accessions of cowpea and wild Vigna germplasm from different parts of the world were assembled in the IITA gene bank. These genetic resources have been explored to identify new traits and to develop elite cowpea varieties. Many cowpea varieties with high yield potential have been developed and adopted by the farmers. Efforts are continuing to develop better performing varieties using conventional breeding procedures, while molecular tools are being developed to facilitate progress in cowpea breeding.