INTERACTION BETWEEN FUSARIUM WILT RESISTANCE GENES IN TOMATO AND FUSARIUM OXYSPORUM F. SP. LYCOPERSICI RACES 1 AND 2

Fusarium wilt of tomato, caused by the soil-borne pathogen Fusarium oxysporum f. sp. lycopersici (Fol), is an important disease responsible for significant economic losses. Resistant cultivars introgressed with the I, I-2 and/or I-3 resistance genes have become the most effective method for controlling this disease. It has been reported that the Avr1 gene of certain isolates of Fol race 1 are able to inhibit the effectiveness of the I-2 and I-3 genes to provide resistance to race 1. In this study, the reaction of seven tomato genotypes containing various combinations of I and/or I-2 was evaluated on plants inoculated with Fol races 1 and 2 individually or jointly. All genotypes containing I were resistant to race 1, and all genotypes lacking I-2 were susceptible to race 2. Inbred lines containing only I were susceptible in both the race 2 inoculation and the combined races 1 and 2 inoculation; although the percentage of susceptible plants in the combined inoculation were significantly less than with race 2 alone. This reduction may have been due to a number of factors including the competition between the races or possibly from the I gene by Avr1 interaction. Inbred lines containing I and I-2 were resistant in the race 2 inoculation and also in the combined races 1 and 2 inoculation. Thus the reported suppression of I-2 by the race 1 Avr1 gene when both races 1 and 2 were present was not observed in this study.