Local and systemic resistance induced in watermelons by formae speciales of Fusarium oxysporum

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