Deepak R. Jadhav

Introgression of Cajanus platycarpus genome into cultivated pigeonpea, C. cajan

SummaryCajanus platycarpus, an incompatible wild species from the tertiary gene pool of pigeonpea (C. cajan (L.) Millspaugh), has many desirable characteristics for the improvement of cultivated varieties. To necessitate such transfers, embryo rescue techniques were used to obtain F1 hybrids. The F1 hybrids were treated with colchicine to obtain tetraploid hybrids, that were selfed to obtain F2, F3 and F4 progenies. All of the hybrids and subsequent progenies had an intermediate morphology between the two parents. Backcrossing of the tetraploid hybrids with cultivated pigeonpea was not possible given embryo abortion, with smaller aborted embryos than those obtained in the F0 parental cross.As a route of introgression, diploid F1 hybrids were backcrossed with cultivated pigeonpea and BC1 progeny obtained by in vitro culture of aborting embryos. BC2 plants were obtained by normal, mature seed germination. Although embryo rescue techniques had to be used to obtain F1 and BC1 plants, it was possible to produce BC2 and subsequent generations through direct mature seed. Every backcross to cultivated pigeonpea increased pollen fertility and the formation of mature seeds.

Screening new Arachis amphidiploids, and autotetraploids for resistance to late leaf spot by detached leaf technique

Cultivated groundnut is susceptible to late leaf spot (LLS) caused by Phaeoisariopsis personata [(Berk. & M.A. Curtis) Aex] and resistance is low to moderate in the primary gene pool of groundnut. Closely related wild species in the secondary gene pool are highly resistant to the disease. All the closely related Arachis species are diploid and cultivated groundnut is a tetraploid. Utilization of diploid Arachis species to transfer LLS resistance is time consuming and cumbersome. New sources of Arachis hypogaea (also called synthetic groundnut) were developed at ICRISAT. These are tetraploids and the present investigation has shown that they are resistant to LLS.

Differences between Cajanus cajan (L.) Millspaugh and C. cajanifolius (Haines) van der Maesen, the progenitor species of pigeonpea

A study was undertaken to know the difference/diversity between pigeonpea and its closely related wild species C. cajanifolius by studying their morphology, crossability, cytology of the hybrid between the two, and molecular studies. Studies revealed that there are at least 5–6 traits that separate the two species such as flower morphology, pod color and morphology, pod constriction, seed color and strophiole, 100 seed weight that separate C. cajan from C. cajanifolius. Molecular studies revealed that a genetic dissimilarity index value ranging from 0.81 to 0.94 exists between the two species.

Cajanus platycarpus (Benth.) Maesen as the donor of new pigeonpea cytoplasmic male sterile (CMS) system

Cajanus platycarpus, a distantly related wild species, was successfully crossed with cultivated pigeonpea using embryo rescue and tissue culture techniques. Advance generation lines showed a range of desirable characters including cytoplasmic male sterility. A range of pigeonpea cultivars restored fertility and was maintained by a few lines including cultivar ICPL 85010. Clasmogamous flowers were observed in the male sterile lines. In such flowers anthers did not form di-adlephous bundle. Cytological analysis revealed that meiosis proceeded normally till the tetrad stage in those anthers with pollen grains. After which many of the pollen grains turned sterile. In the anthers with pollen grains, dehiscence was not observed, thus creating functional sterility. In many other anthers, pollen mother cells (PMCs) were not formed at all, giving rise to sepalous anthers. In conclusion two mechanisms of male sterility existed, one was premeiotic, where PMCs did not form and in the second, although PMCs gave rise to pollen grains, they were either partially or totally sterile accompanied by non-dehiscence of anther wall.