Varietal resistance of lettuce to Fusarium oxysporum f. sp. lactucae

Abstract

After the recent detection of serious losses caused by Fusarium wilt of lettuce, incited by Fusarium oxysporum f. sp. lactucae, in north-western Italy, thirty-two varieties of lettuce, belonging to different types and chosen among those typically grown in the affected area, were tested in order to evaluate the presence of field resistance to Fusarium wilt. Six experimental trials were carried out in glasshouse (4 trials) and growth chamber (2 trials). Roots of 15 day old plants were artificially inoculated by dipping in a spore suspension (1×10 6 CFU/ml) of the pathogen. One Italian isolate (FOL 4) and one American isolate (ATCC 76616) of F. oxysporum f. sp. lactucae were used. In the presence of a good level of disease incidence, a number of varieties, mostly belonging to the leaf lettuce type, were completely resistant to Fusarium wilt. All the tested varieties belonging to the butterhead and most of those belonging to the Batavia types were susceptible to the disease. In the case of the romaine selections, cultivar reaction ranged from susceptible to resistant. In all experiments, the Italian and USA isolates of F. lactucae behaved similarly on all the tested cultivars.