Breeding for Papaya Ringspot Virus Tolerance in Solo Papayas, Carica papaya L.

Zee, Francis T.P.
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A high degree of Papaya Ringspot Virus (PRV) tolerance was observed in a dioecious Carica papaya, line 356, introduced from Florida. Upon infection with the virus, plants of line 356 produced mild leaf, stem and fruit symptoms. Fruit distortion was not observed on these plants. Selected females of line 356 were crossed with 'Kapoho', 'Higgins' and 'Waimanalo' to produce lines 402, 410 and 403, respectively. The level of virus tolerance in these hybrids was observed to be intermediate between the 356 and solo parents. A few selected F2 plants had significantly higher PRV tolerance than the solo parents and only a few trees produced distorted fruits. The F2 plants from 402DF1 and 410AF1 were more tolerant to PRV than 403F1 and derived F2's. Selected 410AF2 trees had the highest virus tolerance among the hybrids but fruit quality was unacceptable. The 402DF2 plants were intermediate in virus tolerance, but produced fruits with good eating quality. The cool climate at the Olinda station in Maui provided good growing conditions for 5 wild Carica species and one interspecific hybrid, but did not permit successful interspecific hybridization between Carica papaya and other species. Carica papaya was crossed with C. pubescens, C. monoica and a C. cauliflora x C. monoica hybrid, resulting in fruits with a few seeds, but no viable hybrid plant was produced. The extraction buffer for C. papaya in ELISA was not suitable for PRV detection in other Carica species. Leaf homogenates from C. pubescens and microcarpa were observed to have a certain compound that interfered with PRV detection when mixed with a PRV standard. The higher the concentration of pubescens homogenate in the mixture, the higher the interference effect. This interference compound appeared to interfere with the PRV-y-globulin, is not protein specific and can be destroyed by heat.
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