Phenotyping chickpeas and pigeonpeas for adaptation to drought

The chickpea and pigeonpea are protein-rich grain legumes used for human consumption in many countries. Grain yield of these crops is low to moderate in the semi-arid tropics with large variation due to high GxE interaction. In the Indian subcontinent chickpea is grown in the post-rainy winter season on receding soil moisture, and in other countries during the cool and dry post winter or spring seasons. The pigeonpea is sown during rainy season which flowers and matures in post-rainy season. The rainy months are hot and humid with diurnal temperature varying between 25 and 35°C (maximum) and 20 and 25°C (minimum) with an erratic rainfall. The available soil water during post-rainy season is about 200-250 mm which is bare minimum to meet the normal evapotranspiration. Thus occurrence of drought is frequent and at varying degrees. To enhance productivity of these crops cultivars tolerant to drought need to be developed. ICRISAT conserves a large number of accessions of chickpea (>20,000) and pigeonpea (>15,000). However only a small proportion (<1%) has been used in crop improvement programs mainly due to non-availability of reliable information on traits of economic importance. To overcome this, core and mini core collections (10% of core, 1% of entire collection) have been developed. Using the mini core approach, trait-specific donor lines were identified for agronomic, quality, and stress related traits in both crops. Composite collections were developed both in chickpea (3000 accessions) and pigeonpea (1000 accessions), genotyped using SSR markers and genotype based reference sets of 300 accessions selected for each crop. Screening methods for different drought-tolerant traits such as early maturity (drought escape), large and deep root system, high water-use efficiency, smaller leaflets, reduced canopy temperature, carbon isotope discrimination, high leaf chlorophyll content (drought avoidance), and breeding strategies for improving drought tolerance have been discussed.

Botrytis grey mould of chickpea: a review of biology, epidemiology, and disease management

Botrytis grey mould (BGM), caused by Botrytis cinerea Pers. ex. Fr., is an economically important disease of chickpea (Cicer arietinum L.), especially in areas where cool, cloudy, and humid weather persists. Several epidemics of BGM causing complete crop loss in the major chickpea-producing countries have been reported. The pathogen B. cinerea mainly survives between seasons on infected crop debris and seeds. Despite extensive investigations on pathological, physiological, and molecular characteristics of B. cinerea causing grey mould type diseases on chickpea and several other hosts, the nature of infection processes and genetic basis of pathogen variability have not been clearly established. This lack of information coupled with the need for repeated application of chemical fungicides forced the deployment of host plant resistance (HPR) as a major option for BGM management. Effective and repeatable controlled-environment and field-screening techniques have been developed for identification of HPR. Of the selected portion of chickpea germplasm evaluated for BGM resistance, only few accessions belonging to both cultivated and wild Cicer spp. were tolerant to BGM, and the search for higher levels of disease resistance continues. Fungicide application based on disease predictive models is helpful in precision-based fungicide application. Integrated disease management (IDM) of BGM has proved more effective than any of the individual disease management components in large-scale, on-farm studies conducted in India, Nepal, and Bangladesh. Further information on the biology of B. cinerea and epidemiology of the disease is needed to strengthen the IDM programs. In this paper the biology of B. cinerea including its variability, epidemiology of BGM, identified sources of resistance, and other management options, and available information on biochemical and genetic basis of disease resistance have been reviewed with a mention of future research priorities.

Ascochyta blight of chickpea (Cicer arietinum L.): a review of biology, pathogenicity, and disease management

Ascochyta blight (AB), caused by Ascochyta rabiei is a major disease of chickpea (Cicer arietinum L.), especially in areas where cool, cloudy, and humid weather persists during the crop season. Several epidemics of AB causing complete yield loss have been reported. The fungus mainly survives between seasons through infected seed and in infected crop debris. Despite extensive pathological and molecular studies, the nature and extent of pathogenic variability in A. rabiei have not been clearly established. Accumulation of phenols, phytoalexins (medicarpin and maackiain), and hydrolytic enzymes has been associated with host-plant resistance (HPR). Seed treatment and foliar application of fungicides are commonly recommended for AB management, but further information on biology and survival of A. rabiei is needed to devise more effective management strategies. Recent studies on inheritance of AB resistance indicate that several quantitative trait loci (QTLs) control resistance. In this paper we review the biology of A. rabiei, HPR, and management options, with an emphasis on future research priorities.

A gene for leaf necrosis in chickpea (Cicer arietinum L.)

Necrosis of leaves was observed in the glabrous mutant (ICC 15566) of desi chickpea (Cicer arietinum L.). It was characterized by drying of leaflet margins to drying of complete leaflets of older leaves. The oldest leaves were the most affected and the intensity of necrosis decreased toward the apical meristem. A single recessive gene, designated nec, was found to govern the necrotic characteristic. The nec locus was linked to gl (glabrous shoots) with a map distance of 16 +/- 3 cM. The loci slv (simple leaves), mlv (multipinnate leaves), nlv (narrow leaflets), hg (prostrate growth habit), P (pink corolla), and shp (round seed shape) segregated independently of nec.

Isozyme polymorphism and phylogenetic interpretations in the genus Cicer L

Allozyme variation among 50 accessions representing the cultivated chickpea (Cicer arietinum L.) and eight wild annual Cicer species was scored and used to assess genetic diversity and phylogeny. Sixteen enzyme systems revealed 22 putative and scorable loci of which 21 showed polymorphism. Variation was prevalent between species (Dst = 0.510) but not within species (Hs = 0.050). No variation for isozyme loci was detected in the cultivated chickpea accessions. Cicer reticulatum had the highest proportion of polymorphic loci (0.59) while the loci Adh-2 and Lap were the most polymorphic over all the species accessions. The phylogeny of annual Cicer species, as determined by allozyme data, generally corroborated those based on other characters in previous studies. Cicer arietinum, C. reticulatum and C. echinospermum formed one cluster, while C. pinnatifidum, C. bijugum and C. judaicum formed another cluster. Cicer chorassanicum was grouped with C. yamashitae, whereas C. cuneatum formed an independent group and showed the largest genetic distance from C. arietinum.

Duplication of the structural gene for the plastid-specific isozyme of aldolase in Cicer

Fructose-bisphosphate aldolase (ALD, EC 4.1.2.13) was analysed in Cicer arietinum L. (the cultivated chickpea) and all eight annual wild Cicer species, C. bijugum Rech., C. chorassanicum (Bge.) M. Pop., C. cuneatum Rich., C. echinospermum Davis, C. judaicum Boiss., C. pinnatifidum J. &S., C. reticulatum Lad., and C. yamashitae Kit. Duplicate genes were identified for the plastid-specific isozyme of ALD in C. arietinum and all wild species except C. yamashitae and one accession of C. reticulatum. Gene duplication was indicated by the presence of a true-breeding five-banded zymotype of the tetrameric plastid ALD in these species. Monogenic inheritance was confirmed for the alleles of one of the loci. The occurrence of ALD gene duplication in most of the annual Cicer species suggests that this duplication is of ancient origin. However, this duplication must have occurred after divergence of Cicer from the closely related genera Pisum and Lens because the plastid ALD is controlled monogenically in these latter two genera.Key words: Cicer, isozymes, aldolase, gene duplication.

Genetic control and linkage relations of additional isozyme markers in chick-pea

Allozyme polymorphisms of nine enzymes - aspartate aminotransferase (AAT), diaphorase (DIA), esterase (EST), formate dehydrogenase (FDH), β-galactosidase (GAL), β-glucosidase (GLU), malate dehydrogenase (MDH), malic enzyme (ME), and peroxidase (PRX) - were described in chick-pea (Cicer L.). Thirteen isozyme loci, Aat-c, Dia-4, Est-2, Est-4, Est-10, Fdh, Gal-2, Gal-3, Gal-4, Glu-3, Mdh-2, Me-2, and Prx-2, were genetically defined. Alleles of each of these isozyme loci expressed codominantly in heterozygotes and exhibited a codominant, single-locus segregation ratio in F2. The loci Est-2, Mdh-2, and Me-1 were expressed only in flower. Linkage relations were determined for these 13 and several previously defined isozyme loci. The following new genetic linkages were identified: Pgm-p (locus for plastid phosphoglucomutase) - Est-10; Ald-p1 (one of the duplicate loci for plastid aldolase) - Glu-3 - Gal-2 - Est-2,3; Gal-3 - Aco-m (locus for mitochondrial aconitase) - Prx-2,3; Gpi-c (locus for cytosolic glucosephosphate isomerase) - Fdh; and Est-4 - Me-1. This study provides further confirmation on the existence of several conserved linkage groups among Cicer, Pisum, and Lens.