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.
3. Progress Report:
This project supported a total of 4 subprojects covered under this progress report. Of the 4 subprojects, 3 were funded and carried over from 2010 and one received funding in 2011. 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 the source of P. palmivora resistance. Achievements have 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 a new source of resistance genes for P. palmivora could be an effective tool for developing transgenic strategies than that was previously used. Attempts have been 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 been successful in developing a BC3 generation, which is expected to produce its first Super Rainbow seed soon. When the Super Rainbow line is developed, Hawaii, will be in a better position to cope with the potential risks if and when a new PRSV strain, capable of overcoming the resistance of the exiting Rainbow papaya, is introduced or evolved. To study the handling and storage of a new papaya variety, the QTL softening segregation study through modifying ethylene production in ripening papaya was conducted to determine the ripening characteristics of a new papaya line. In addition, crosses between the slow-ripening line and the virus resistant line “SunUP” have been made to develop a homozygous virus-resistant slow-ripening line. After confirming that the crosses contained the transgene for virus resistance, selection was made and trees with low summer sterility and slow ripening characteristics were replanted in the field.