Genetic diversity and identification of race 3 of Fusarium oxysporum f. sp. lactucae in Taiwan

Fusarium wilt disease of lettuce (Lactuca sativa L.) is one of the major threats to the production of lettuce in Taiwan. This disease is caused by the vascular wilt pathogen Fusarium oxysporum f. sp. lactucae. It is important for the lettuce breeders to identify the pathological races of F. oxysporum f. sp. lactucae in the course of developing F. oxysporum f. sp. lactucae-resistant cultivars for growers. Recently, race 3 of F. oxysporum f. sp. lactucae was identified in Taiwan based on the results of pathogenicity tests against three differential lettuce cultivars, Patriot, Costa Rica No. 4, and Banchu Red Fire, along with some Japanese F. oxysporum f. sp. lactucae reference strains for comparison. In our collected F. oxysporum f. sp. lactucae isolates, most isolates from Taiwan were identified as race 1 except two isolates, Fola-10 and Fola-40 collected from Taoyuan County identified as race 3. This is the first report of F. oxysporum f. sp. lactucae race 3 outside of Japan. The PCR-based tagging technique with the four reference markers was used to confirm the results of pathogenicity tests. In addition, genetic diversity between races of F. oxysporum f. sp. lactucae was also observed according to the results of random amplification of polymorphic DNA (RAPD) fingerprintings.