GREENHOUSE AND FIELD EVALUATIONS OF COAT-PROTEIN TRANSGENIC PAPAYA RESISTANT TO PAPAYA RINGSPOT VIRUS

Abstract

The coat protein (CP) gene of a Taiwan strain of papaya ringspot virus (PRSV) was efficiently transferred to papaya by Agrobacterium-mediated transformation, assisted by wounding of embryogenic tissues derived from immature zygotic embryos with carborundum in liquid phase. Thirty-eight transgenic lines were micropropagated by tissue culture and their resistance to PRSV was evaluated by mechanical inoculation with the virus under greenhouse conditions. Among them, 9 lines were found highly resistant to PRSV and 8 lines moderately resistant. The highly resistant lines also conferred broad-spectrum resistance to PRSV strains from Thailand and Hawaii. Three lines of transgenic papaya, 16-0-1, 17-0-1 and 17-0-5, were further evaluated under field conditions in two different locations, the first started from January 1996 and the second from August 1996. In the first trial, only 0, 2, and 0% of lines 16-0-1, 17-0-1 and 17-0-5 (each with 100 plants tested), respectively, were infected by PRSV 12 months after planting, while the control plants were 100% infected eight months after planting. The transgenic lines in the second trial, which were under a severe challenge pressure, had infection rates of 10-20% five months after planting, while the control was completely infected three months after planting. The preliminary results of the field tests indicated that the CP transgenic papaya lines have a great potential for control of PRSV in Taiwan.