Effects of turnip mosaic virus and turnip yellow mosaic virus on the survival, growth and reproduction of wild cabbage (Brassica oleracea)

Wild plants of Brassica oleracea (wild cabbage) are commonly infected with turnip mosaic potyvirus (TuMV), turnip yellow mosaic tymovirus (TYMV) and s everal other viruses. A field experiment in which plants were inoculated ei ther with TuMV or TYMV showed that virus infection significantly reduced su rvival, growth and reproduction. Relative to water inoculated-controls, pla nts infected with TYMV had greater mortality, were shorter, had a smaller l eaf area and number, showed a greater amount of damage from herbivory and c hlorosis, were less likely to flower and produced fewer pods and lower tota l seed output. Plants infected with TuMV did not appear to be adversely aff ected at first; however, mortality after 18 months was higher than control plants. Although TuMV infection had no effect on the number of plants flowe ring, the infected plants did produce fewer pods and a lower total seed out put. We conclude that both viruses can significantly affect vegetative and reproductive performance of wild cabbage and hence that introgression of vi rus resistance (particularly when conferred by a major gene or a transgene) from a crop might increase plant fitness in natural populations of this sp ecies. Ecological risk assessments of virus resistance transgenes must do m ore than survey adult plants in natural populations for the presence of the target virus. Failure to detect the virus could be due to high mortality o n infection with the virus.