Reaction of lettuce cultivars to fusarium wilt (fusarium oxysporum f.sp. Lactucum)

Fusarium wilt of lettuce caused by the fungus Fusarium oxysporum f.sp. lactucum is a destructive disease of lettuce in fields of Tehran province. A glasshouse experiment was conducted to evaluate resistance and susceptibility of 20 lettuce cultivars obtained from, Denmark, Italy, England, USA and Iran to an aggressive isolate of the pathogen. The Index of percentage of seed germination, number of healthy plants, fresh and dry weight of shoots and dry weight of roots were used for cultivar evaluation. Results indicated that Salinas and Grand Rapids were the most resisitant cultivars base on the mentioned index (P < 0.05). In the field experiment nine cultivars were planted in soil with 30% infection during the previous year. A Randomized Complete Block Design with four replications was used. Plants were inoculated around the roots at the two leaf stage with spore suspension of the pathogen isolate. Results indicated that local cultivars curl Ahwazi and Esfahani with no infection were resistant. Black Shahre-Ray and King Crown with 18.42% and 26.2% of infection respectively, showed an intermediate reaction to the pathogen.