Submitted to: Acta Horticulture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/20/2002
Publication Date: 4/30/2002
Citation: Fitch, M.M., Leong, T., Akashi, L., Ferreira, S., Moore, P.H. 2002. Papaya ringspot virus resistance genes as a stimulus for developing new cultivars and new production systems. Acta Horticulturae 575: 85-91. 2002
Interpretive Summary: The development of virus resistant papayas by scientists at ARS, the University of Hawaii, and Cornell University helped foster new research in breeding and methods of plant propagation. Crossing virus resistant and traditional varieties resulted in new varieties that replaced the virus susceptible ones. Field tests comparing varieties and different propagation systems could be completed without the threat of destruction by the virus. Farmers benefited by having a wider range of varieties to grow in specialized areas and consumers could choose from several types of papayas at reasonable prices.
Technical Abstract: Transgenic papaya ringspot virus (PRSV) resistant cultivars have revitalized a papaya industry that nearly collapsed following an outbreak of PRSV. Other crop production challenges remain, for example, the agronomic practice of direct multiple seeding for later thinning to a single hermaphrodite tree remains wasteful of seed, labor, and resources. In addition, Hawaii's major papaya production region with rocky, shallow soil and high rainfall could expand to more highly productive deep, irrigated soils if cultivars selected for these environments were also resistant to PRSV. We developed clonal propagation systems to replace multiple seedlings. Growth and yield trials showed that the clonally propagated plants bore fruit earlier, lower on the trunk, and could be harvested without extra equipment for a longer period than could seedlings. We developed new PRSV resistant cultivars by direct genetic transformation and also introgressed the PRSV resistance gene from Rainbow F2 progeny into the soil-adapted, Phytophthora-tolerant cultivar Kamiya. The fruit of Kamiya is distinguished from that of Rainbow in that it is larger with a thick orange-yellow flesh and flavors reminiscent of coconut or mango. Both hybridization and transformation programs produced PRSV resistant lines of Kamiya. Rainbow F2 plants have also been backcrossed with their firm-fleshed Kapoho parent to improve shipping and handling qualities while maintaining resistance to PRSV and Phytophthora. Progeny from these crosses are performing well and may lead to the development of new cultivars. Results of evaluation trials will be given.