Broad-based resistance to pigeonpea sterility mosaic disease in wild relatives of pigeonpea (Cajanus : Phaseoleae)

Sterility mosaic disease (SMD), an important biotic constraint on pigeonpea (Cajanus cajan) in the Indian subcontinent, is caused by Pigeonpea sterility mosaic virus (PPSMV) transmitted by the eriophyid mite, Aceria cajani. Distinct PPSMV isolates occur in different geographical regions and broad-based resistance to all these isolates is scarce in cultivated pigeonpea germplasm. Wild relatives of pigeonpea, which are known to possess resistance to several pests and diseases, were evaluated for broad-based SMD resistance. One hundred and fifteen wild Cajanus accessions from six species (C. albicans, C. platycarpus, C. cajanifolius, C. lineatus, C. scarabaeoides and C. sericeus) were evaluated against three PPSMV isolates prevailing in peninsular India. Evaluations were done under greenhouse conditions in endemic locations of each isolate through mite-mediated virus inoculation. Fifteen accessions showed, resistance to all three isolates: ICP 15614, 15615, 15626, 15684, 15688, 15700, 15701, 15725, 15734, 15736, 15737, 15740, 15924, 15925 and 15926. Most of the wild accessions did not support mite multiplication. The majority of the accessions resistant to PPSMV following inoculations with viruliferous mites were susceptible by graft inoculation, suggesting that vector resistance is conferring resistance to infection with PPSMV. The 15 accessions identified as being resistant to infection to all three virus isolates tested are cross compatible with pigeonpea by traditional breeding. They are therefore useful for exploitation in breeding programmes to increase both the level of SMD resistance and to diversify its genetic base in the cultivated pigeonpea gene pool.