Fusarium wilt race 1 on lettuce

Three races of Fusarium oxysporum f.sp. lactucae, cause of fusarium wilt of lettuce, are known in Japan, where the pathogen was first observed in 1955. Fusarium wilt first affected commercial U.S. lettuce production in 1990 in Huron, Calif., but did not become a serious problem in the U.S. until 2001 when it reappeared in Huron and appeared in the Yuma, Arizona lettuce production area. Reactions of three fusarium wilt differentials ('Patriot', susceptible to races 1,2 and 3; 'Costa Rica No. 4', resistant to race 1, and susceptible to races 2 and 3; and 'Banchu Red Fire', susceptible to races 1 and 3, and resistant to race 2) in a naturally-infected commercial field test and artificially-inoculated greenhouse tests, indicated presence of race 1 in the Yuma lettuce production area. Reactions of these differentials to an isolate from Huron confirmed the presence of race 1 in that area. Consistent with previous results from the U.S. and Japan, 'Salinas' and 'Salinas 88' were resistant to the Yuma and Huron isolates of race 1, whereas 'Vanguard' was highly susceptible. Limited F₁ and F₂ data indicate that resistance to race 1 in 'Costa Rica No. 4' and 'Salinas' is recessive. 'Calmar' is the likely source of resistance in 'Salinas' and 'Salinas 88'.