Conventional and biotechnology-assisted breeding in developing ringspot virus resistant papaya
2002
Villegas, V.N. (Philippines Univ. Los Banos, College, Laguna (Philippines). Inst. of Plant Breeding)
Papaya ringspot virus (PRSV-P) is a major disease of papaya in the Philippines. PRSV-P infected plants exhibit leaf mottling, reduced lamina, tapering of stem, oil streaks on petioles and ringspots in the fruits. Screening available germplasm revealed that resistance is not found within the cultivated Carica papaya species. Three approaches are being utilized to develop PRSV-P resistant papaya. Intraspecific hybridization produced a moderately tolerant variety and identified tolerant genetic stocks. Interspecific hybridization, done by crossing papaya with PRSV-P resistant wild relatives (e.g., C. cauliflora, C. quercifolia, C. pubescens), produced resistant hybrids. However, sterility and hybrid breakdown hamper the backcrossing procedure to transfer the resistance trait to papaya. Genetic engineering is another technique being pursued and this works on the principle of coat protein-mediated resistance. Coat protein gene from the local virus isolate had been cloned and inserted into Davao solo papaya via microprojectile bombardment. Putative transformants are on the regeneration stage. International collaboration has played an important role in the authors' efforts to develop PRSV-P resistant papaya. Details of the progress made using intra-specific and inter-specific hybridization and genetic engineering are discussed
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