Analysis on virus resistance and fruit quality for T4 generation of transgenic papaya

Molecular biological characterization,fruit char-acters,and nutrients were analyzed for T4 generation of transgenic papaya.All transgenic papaya plants with the mutated replicase(RP)gene from papaya ringspot virus(PRSV)showed high resistance or immunity against PRSV in the field.The RP transgene can be steadily inherited to,and expressed at RNA level,the progenies.The growth char-acteristics of transgenic papaya were much better than non-transgenic papaya in the field.The non-transgenic papaya seedlings began to show typical symptoms caused by PRSV after being inoculated with PRSV.They died quickly and never grew to produce fruit.The adult trees developed yellow leaves and produced smaller fruits and were doomed to a slow death after some time,while most of transgenic papaya plants(about 91.8%)did not show any symptoms caused by PRSV,and produced more,bigger,and high quality fruits.Compared with non-transgenic plants,the fresh fruit length of T4 gen-eration of transgenic papaya increased 2.6%-5%,and the diameter decreased 0.6%-1.5%.The flesh thickness of fresh fruit increased 12%-15%,which made it fitter for eating.Although the fresh fruit quality changed,there was no sig-nificant difference between transgenic and non-transgenic papaya.The quality characteristics of dry fruit including the contents of water,lipid,N,protein,reduced sugar,vitamin A,vitamin C,and carotene in the T4 generation of transgenic papaya were all the same as their non-transgenic parents.This means that transgenic plants and non-transgenic plants are substantially equivalent,and the transgene has no effect on dry fruit quality.In this study,we found that vitamin A and vitamin C in red-fleshed papaya were 1.4-1.8 and 1.78-2.07 times more than the yellow-fleshed ones,respectively,while N and protein were only 84.2%-92.1%and 82.1%-98.9%of the yellow-fleshed ones.