VIEW ARTICLE

Resistance

Local and Systemic Resistance Induced in Watermelons by Formae Speciales of Fusarium oxysporum. C. L. Biles, Graduate research assistant, Department of Plant Pathology and Microbiology, Texas A&M University, College Station 77843; R. D. Martyn, associate professor, Department of Plant Pathology and Microbiology, Texas A&M University, College Station 77843. Phytopathology 79:856-860. Accepted for publication 1 April 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-856.

Watermelon cultivars differentially resistant to Fusarium wilt were preinoculated (induced) with Fusarium oxysporum f. sp. cucumerinum or avirulent races of F. o. niveum 24 or 72 hr prior to challenge with a virulent race of F. o. niveum. All of the inducer treatments significantly reduced wilt symptoms (P= 0.05). Avirulent races of F. o. niveum induced a higher level of resistance than did F. o. cucumerinum. An interval of 24 hr between induction and challenge provided significant protection; a 72-hr interval further enhanced resistance. When roots of the wilt-susceptible watermelon cultivar Black Diamond were induced with F. o. cucumerinum and the leaves inoculated with Colletotrichum lagenarium 24 or 72 hr later, 50% fewer lesions developed on leaves of induced plants than on noninduced inoculated controls. This suggests that induced resistance to F. o. niveum is both local and systemic, as well as nonspecific.