ETHYLENE REGULATES THE SUSCEPTIBLE RESPONSE TO PATHOGEN INFECTION IN TOMATO

Ethylene evolution occurs concomitantly with the progression of diseas e symptoms in response to many virulent pathogen infections in plants. A tomato mutant impaired in ethylene perception-Never ripe-exhibited a significant reduction in disease symptoms in comparison to the wild type after inoculations of both genotypes with virulent bacterial (Xan thomonas campestris pv vesicatoria and Pseudomonas syringae pv tomato) and fungal (Fusarium oxysporum f sp lycopersici) pathogens. Bacterial spot disease symptoms were also reduced in tomato genotypes impaired in ethylene synthesis (1-aminocyclopropane-1-carboxylic acid deaminase ) and perception (14893), thereby corroborating a reducing effect for ethylene insensitivity on foliar disease development. The reduction in foliar disease symptoms in Never ripe plants was a specific effect of ethylene insensitivity and was not due to reductions in bacterial pop ulations or decreased ethylene synthesis. PR-1B1 mRNA accumulation in response to X. c. vesicatoria infection was not affected by ethylene i nsensitivity, indicating that ethylene is not required for defense gen e induction. Our findings suggest that broad tolerance of diverse vege tative diseases may be achieved via engineering of ethylene insensitiv ity in tomato.