Genetic Resources, Chromosome Engineering, and Crop Improvement

Grain Legumes, Volume I

Ram J. Singh, Prem P. Jauhar

• Publisher: CRC Press
• Year: 2005
• ISBN:
  9781135509682
• Edition: 1
• Topic: Ciencias biológicas
• Subtopic: Botánica

The first book in this new series discusses grain legumes, which rank only second to cereals in supplying calories and protein to the world's population. With each chapter written by an internationally renowned scientist, the book reviews the role of alien germplasm for the domestication of each major legume crop. Discussion for each crop covers or

CHAPTER 1: Landmark Research in Grain Legumes

Ram J.Singh

1.1 INTRODUCTION

The primary dietary grain legumes included in this series are the common bean (Phaseolus vulgaris L.), cowpea [Vigna unguiculata (L.) Walp.], pigeonpea [Cajanus cajan (L.) Millsp.], chickpea (Cicer arietinum L.), faba bean (Vicia faba L.), lentil (Lens culinaris Medik.), mungbean [Vigna radiata (L.) Wilczek], azuki bean [Vigna angularis (L.) Ohwi & Ohashi], and pea (Pisum sativum L.). Several species of lupin are used primarily for animal feed in Australia and as a forage crop in Europe. The hallmark trait of legume species is their high protein content (see Table 1.1).

Grain legumes and cereals co-evolved in a symbiotic way. They are complementary components of agricultural systems worldwide, including common bean and maize in South America; lentil, pea, chickpea, faba bean, bitter vetch with two wheats (durum and einkorn), as well as barley in the Middle East; soybean with millet in North China; and Vigna bean (and soybean-rice, later) in

South China (José Cubero; personal communication, May 26, 2004). In Africa, cowpea grows with pearl millet and sorghum.

Grain legumes are members of the family Fabaceae. The major agricultural legumes are divided into two main groups. The warm-weather group contains Vigna, Phaseolus, Cajanus, and Glycine. The cool-season group includes Vicia, Pisum, Trifolium, and Lotus (see Chapter 11). This volume includes major grain legumes of both groups that are used for food and feed. The terms grain legume and pulse need clarification. Grain legume refers to the legume species of which the edible part is seed (food and feed). Pulse is derived from the Latin word that means “pottage” and mainly refers to food legumes. Soybean [Glycine max (L.) Merr.] and groundnut (peanut) (Arachis hypogea L.) were, in fact, pulses at the very beginning. However, now they are considered oilseed crops because they contain more than 20% oil and are used extensively for oil and meal (K. Siddique; personal communication, May 18, 2004).

The characteristic feature of legumes is the presence of root nodules, which contains the bacterium Rhizobium, and related genera, that helps nitrogen fixation in the soils, maintaining a symbiotic relationship. However, such bacterial association is absent in cereals. Grain legumes are rich in protein (20 to 50%), while cereals are an excellent source of carbohydrates. The combination of cereals and grain legumes enriches the human diet, especially when supplementing the protein requirement. Grain legumes are an important source of protein in countries where the majority of people are vegetarian both by choice and due to religious beliefs, such as India. However, in Central America and the Caribbean, rice and beans is a staple dish, even though most people are not vegetarian.

Grain legumes are second only to cereals in their dietary importance to humans and animals (Graham and Vance, 2003). Although grain legumes are an extremely valuable source of protein for both humans and animals, research efforts for producing high-yielding cultivars of grain legumes lag far behind that of cereals. The poor yield of grain legumes may be due to the growing of inherently unproductive cultivars that are not tolerant to abiotic and biotic stresses. Grain legumes are often cultivated as subsistence crops in smallholdings and for home consumption as part of the “kitchen garden.” Compared with cereals, research on pulse crops has been largely neglected in developing countries. This chapter summarizes landmark research efforts in 10 major grain legumes.

1.2 ESTABLISHMENT OF INTERNATIONAL AND NATIONAL PROGRAMS

The following international and national centers have been established for major grain legume research:

1. Centro Internacional de Agricultura Tropical (CIAT), Cali, Colombia (http://www.ciat.cgiar.org/): Common bean is a mandate crop.
2. International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru, India (http://www.icrisat.org/): Pigeonpea and chickpea are mandate crops.
3. International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria (http://www.iita.org/): Cowpea is a mandate crop.
4. International Center for Agricultural Research in the Dry Areas (ICARDA), Aleppo, Syria (http://www.icarda.org/): Chickpea, lentil, and faba bean are mandate crops. The center also maintains pea germplasm but has no active varietal improvement programs.
5. Asian Vegetable Research and Development Center (AVRDC), Taiwan (http://www.avrdc.org/): Mungbean is a mandate crop, and the center has the largest germplasm collection of this crop. Major collections of the related azuki bean are held at AVRDC and in national collections of China and Japan.
6. National Programs: National (public) and private industries worldwide have legume improvement programs.

Figure 1.1 Gene pool concept in plants established based on hybridization. (Modified and redrawn from Harlan and de Wet, 1971.)

1.3 GENE POOLS FOR GRAIN LEGUMES

The gene pool concept developed by Harlan and de Wet (1971) has played a pivotal role in the utilization of germplasm resources for producing high-yielding cultivars without antinutritional chemicals by conventional methods and by transformation technology. Harlan and de Wet (1971) proposed three gene pool concepts based on the results of hybridization among species. These are primary (GP-1), secondary (GP-2), and tertiary (GP-3) (Figure 1.1).

1.3.1 Primary Gene Pool

The primary gene pool (GP-1) of grain legumes consists of landraces and biological species. Crossing within this gene pool is easy and hybrids are vigorous, exhibit normal meiotic chromosome pairing, and possess total fertility. The gene segregation in F₁ is normal and gene exchange is generally easy. Primary gene pool A includes cultivated races and landraces. Primary gene pool B includes subspecies, wild and weedy relatives (see Figure 1.1). Table 1.1 lists the primary gene pool of grain legumes.

1.3.2 Secondary Gene Pool

The secondary gene pool (GP-2) includes all species that can be crossed with GP-1 with at least some fertility in F₁s (see Figure 1.1). Gene transfer is possible with some difficulty. In this regard, GP-2 for common bean, pigeonpea, chickpea, lentil, mungbean, and azuki bean is availableand can be used in varietal improvement. Cowpea and faba bean do not have a GP-2, and thereare no GP-1 relatives of faba bean (see Table 1.1).

Table 1.1 Common Name, Scientific Name, 2n Chromosome Number, Origin, and Gene Pools of Major Grain Legumes

1.3.3 Tertiary Gene Pool

The tertiary gene pool (GP-3) is the extreme outer limit of potential genetic resource (see Figure 1.1). Table 1.1 lists GP-3 of pigeonpea, cowpea, chickpea, lentil, lupin, mungbean, and azuki bean. Pea and faba bean are without GP-3 (see Table 1.1). Prezygotic and postzygotic barriers can cause partial or complete failure of hybridization, inhibiting introgression between GP-1 and GP-3. The exploitation of wild relatives of grain legumes is often hampered by poor crossability, early embryo abortion, hybrid inviability, hybrid seedling lethality, and hybrid sterility due to low chromosome pairing. Technology to exploit GP-3 for broadening the genetic base of grain legumes is yet to be developed.

1.4 GERMPLASM RESOURCES FOR GRAIN LEGUMES

The international and national institutes for grain legumes (common bean, pea, pigeonpea, cowpea, faba bean, chickpea, lentil, lupin, mungbean, azuki bean) collect, maintain, disseminate, and develop breeding lines with resistance to abiotic and biotic stresses. Plant exploration of wild relatives, often described as “exotic” germplasm, of common bean, faba bean, lentil, chickpea, and cowpea is extensive. Although pea is an important legume, it does not have an international institute for its research, but several national research institutes maintain active breeding programs (see Chapter 3). The National Institute of Agrobiological Sciences in Japan has a very active research program for the Asian Vigna, which includes mungbean (see Chapter 10) and azuki bean (see Chapter 11).

Wild relatives of major grain legumes included in this volume are being characterized based on classical taxonomy, cytogenetics, and molecular methods. The combination of the genus Atylosia with the genus Cajanus is a classic example (van der Maesen, 1986; Chapter 4).

Cytogenetics of grain legumes has not progressed as rapidly as for cereals, although the foundation of genetics was laid by Johann Gregor Mendel’s pea experiments. Simultaneously, Galton developed “Biochemical or Quantitative Genetics” by using Lathyrus odoratus, which was then a garden plant. Cytogenetics of major grain legumes is lacking—the only exception being faba bean. Taylor et al. (1957) demonstrated semiconservative replication of Vicia faba chromosomes by using tritium-labeled thymidine. Faba bean and onion root tips were used for studying cell division and cytogenetics because their chromosomes are large, few in number, and stain very well. They were the model crops used to study the effect of chemicals on chromosome structure.

Cytogenetic stocks and molecular maps of grain legumes are being developed in common bean and faba bean. A composite molecular map has been successfully developed including morphological markers, isozymes, random amplified polymorphic DNAs (RAPDs), sequence-characterized amplified regions (SCARs), seed protein genes, and microsatellites. Using trisomics, the linkage groups of faba bean have been placed in their respective chromosomes; for the long metacentric chromosome, whose trisomics could not be obtained, some markers were developed to build up its linkage map. The linkage groups have so far been obtained to cover about 1600cM with an overall map interval of 8cM. Several important characters have been mapped, such as genes and quantitative trait loci (QTLs) for resistance to ascochyta, rust, and broomrape resistance, as well as for the two main antinutritional factors. In this map, genes controlling important characters of both qualitative (Mendelian) and quantitative (QTLs) natures are being placed. Marker-assisted selection (MAS) and studies on synteny are breeders’ ultimate objectives (see Chapter 6).

The impact of somaclonal variation and genetic transformation for producing better grain legumes is limited. Genetically modified grain legumes are being produced in several laboratories by transformation; however, they have not been released for commercial production.

Some high-yielding legume cultivars are eroding the natural habitat of the allied species and genera. It is very important, therefore, that these invaluable germplasm resources are collected before they become extinct. The international and national institutes are preserving indigenous varieties, landraces, and wild relatives in medium-and long-term storages and their viability is checked routinely.

1.5 GERMPLASM ENHANCEMENT FOR GRAIN LEGUMES

The genetic base of grain legumes is rather narrow because breeders have been confined in their crop improvement programs to GP-1 (primitive cultivated forms, landraces, and wild progenitors). Although GP-2 has been used to improve common bean, it is beyond reach for improving lentil (see Chapter 8). GP-3 has not been exploited to introgress traits of economic importance in cultivated legume species. A large number of exotic accessions are stored in seed banks worldwide (Tanksley and McCouch, 1997). However, only a fraction of valuable genes has been tapped for improving legumes. Conventional breeding (selection from landraces and primitive cultivars, pedigree, bulk, backcross, or single-seed descent methods of selection), mutation breeding, exploitation of somaclonal variability, and genetic transformation have helped breeders to select superior cultivars of grain legumes. Commercial hybrid production using cytoplasmic male sterility (CMS) is a success story for pigeonpea, where hybrids produced a 4 to 52% increase in yield over the parents. This is feasible because the natural out-crossing in pigeonpea ranges from 20 to 40% (see Chapter 4). Faba bean is also a partially (34%) allogamous crop and cross-pollination ranges from 4% (practically a selfer) to 84% (practically an outcrosser) (see Chapter 6). The major obstacle in producing hybrid legumes is the structure of the flower, which ensures a 99% chance of self-pollination in most grain legumes. Lentil contains small cleistogamous flowers, making it virtually 100% self-pollinating (see Chapter 8). Outcrossing in mungbean is only 0.5 to 3% (see Chapter 10).

1.5.1 Breeding for Plant Type

Breeders have developed determinate semidwarf and dwarf plant types with uniform maturity for common bean, pea, cowpea, faba bean, pigeonpea, lupin, mungbean, and azuki bean by conventional breeding. Semidwarf varieties with determinate plant type are resistant to lodging and therefore adapted to mechanical harvesting. Early maturing (less than 98 days), high-yielding common bean varieties with upright growth habit can be machine harvested, which is cost-effective for common bean growers (see Chapter 2). A major breakthrough in pea came about when breeders combined reduced crop height (e.g., le) and conversion of leaflets to tendrils (e.g., af), described as the semidwarf, semileafless ideotype. The semidwarf and semileafless types provided a number of benefits, such as reduced leafiness and excessive overshading, increased aeration and reduced disease in some environments, and improved ease of harvest of both garden and field pea types as a consequence of reduced lodging (see Chapter 3). An artificially induced mutant for determinate growth in faba bean resulted in a cultivar that facilitated easy machine harvesting (see Chapter 6). Dwarfing genes have been identified in pigeonpea and are being used to develop dwarf cultivars. Most pigeonpea varieties at reproductive stage achieve the height of 2 to 3 m. The dwarf-inbred lines range in height from 70 to 80 cm and produce reasonable yields (see Chapter 4).

1.5.2 Breeding for High Yield

Substantial gain in yield has been achieved in all grain legumes through innovative conventional breeding, but it is still far behind that of cereals. Conventional breeding produced high-yielding cultivars containing genes for resistance to biotic (fungal diseases, viruses, and pests) and abiotic (cold, heat, drought, adverse soil nutrition, and lodging) stresses. High-yielding pigeonpea varieties have been produced by mutation breeding (see Chapter 4). A somaclonal variant in pigeonpea also produces white ...

Table of contents

• Cover Page
• Genetic Resources, Chromosome Engineering, and Crop Improvement Series
• Title Page
• Copyright Page
• Dedication
• Preface
• The Editors
• Contributors
• CHAPTER 1: Landmark Research in Grain Legumes
• CHAPTER 2: Common Bean (Phaseolus vulgaris L.)
• CHAPTER 3: Pea (Pisum sativum L.)
• CHAPTER 4: Pigeonpea [Cajanus cajan (L.) Millsp.]
• CHAPTER 5: Cowpea [Vigna unguiculata (L.) Walp.]
• CHAPTER 6: Faba bean (Vicia faba L.)
• CHAPTER 7: Chickpea a (Cicer arietinum
• CHAPTER 8: Lentil (Lens culinaris Medik.)
• CHAPTER 9: Lupin
• CHAPTER 10: Mungbean [Vigna radiata (L.) Wilczek]
• CHAPTER 11: Azuki Bean [Vigna angularis (Willd.) Ohwi & Ohashi