1a. Objectives (from AD-416)
Develop and evaluate non-toxic, preferably biologically-based, environmentally suitable technologies and processes for pest and disease control on papaya. Evaluate existing, or breeding new, papaya varieties for desirable fruit quality and shelf life and for high degree of tolerance or resistance to fungal diseases, such as Phytophthora.
1b. Approach (from AD-416)
A research team consisting of faculty and researchers from the University of Hawaii(UH) and Pacific Basin Agricultural Research Center (PBARC) with expertise in papaya breeding, plant protection (particularly in plant pathology), and genetic engineering will develop an achievable and measurable action plan to accomplish the objectives identified above. The team shall share research responsibilities in papaya breeding, evaluating tolerance or resistance against fungal diseases and papaya ringspot virus, and studying the shelf life of papaya varieties evaluated or bred. Documents SCA with U of HI. Formerly 5320-22430-021-10S term 9/27/2010.
3. Progress Report
This project supported a total of 7 subprojects covered in this progress report. Despite insecticide applications, a high density of Thrips parvispinus, a newly discovered pest of papaya, continued to be found in a farm suggesting that this species might have developed insecticide resistance. This underscores the need for more sustainable pest management strategies to target this pest. It was also shown that flower age seems to play an important role in determining thrips density. This can potentially be useful in development of a timely control strategy against this thrips. Using microsatellite markers, population differentiations were determined in Pentalonia (9 loci), Aphis gossypii (10 loci) and Myzus persicae species (11 loci). Further using the structure analysis, it was revealed that there are 2 genetic clusters from each of Pentalonia (P. nigronervosa and P. caladi), A. gossypii, and M. persicae. The genetic structuring of these four aphid species showed a significant association of these species to host plant and islands except for M. persicae which showed no association between its population and the island. The close association between aphid clusters and host plant resulted in the formation of specialized host races in aphids; P. nigronervosa closely associated with Musaceae and the P. caladii subspecies associated with Zingiberaceae. The project also confirmed that all these aphids reproduce asexually in Hawaii. All of the Phytophthora resistance genes identified so far belonged to the NBS superfamily of genes; therefore, the NBS gene family of V. goudotiana is most likely to be the source of Phytophthora palmivora resistance. A significant achievement has been made to identify 145 candidate NBS genes. Of which, one of the NBS genes was induced by the pathogen, suggesting it plays a role in plant-pathogen interaction. Identification of such new sources of resistance genes for P. palmivora could be used as a more effective tool for developing transgenic strategies than that was previously attempted. Attempts were made to back cross (BC) Kapoho line with SunUp to produce a Super Rainbow which combines the original cp55-1 transgene and the new segmented transgene construct with component of the cp gene from Thailand, Taiwan and Hawaii. This back crossing has developed a BC3 generation, which is expected to produce its first Super Rainbow seeds in the next 1–1.5 yrs. Consequently, Hawaii will be in a better position to cope with the risk when a new PRSV strain is introduced or when a new PRSV strain, which is capable of overcoming the Rainbow papaya’s resistance, is evolved. Finally, a biological-based approach to postharvest disease control was developed and evaluated. The microorganisms isolated from papaya fruit surface were evaluated for their ability to control postharvest disease through an antagonistic action of a microorganism(s) against the disease carrying microorganisms. Output from this project would provide a postharvest disease control for organic papaya production and serve as an alternative to fungicide in conventional production. The project is monitored via meetings, site visits, phone and email.