Development of Sphaerotheca fusca on susceptible, resistant, and temperature-sensitive resistant melon cultivars

Development of the powdery mildest fungus Sphaerotheca fusca on leaves of s usceptible, resistant and temperature-sensitive resistant melon cultivars a t 21 degreesC and 26 degrees was examined by light and scanning electron mi croscopy, On the susceptible cv, 'Rochet' the time course of the infection process was similar at each temperature, Development of powdery mildew colo nies paralleled the progressive branching of mycelia and conidiophore forma tion. On the resistant cv, PMR-o , however development was arrested at the primary appressorium stage irrespective of the temperature, When the temper ature-sensitive resistant line ANC-57 was infected by a race 1 isolate, inc ubation temperature had a clear effect on the Outcome of the interaction, A t 21 degrees, it took longer for symptoms to appear on cv, ANC-57 than on c v. 'Rochet'. while colonies were limited and sparse, At 26 degrees resistan ce was complete, there being no development.