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

Development of the powdery mildest fungus Sphaerotheca fusca on leaves of susceptible, resistant and temperature-sensitive resistant melon cultivars at 21 degreesC and 26 degrees was examined by light and scanning electron microscopy, On the susceptible cv, 'Rochet' the time course of the infection process was similar at each temperature, Development of powdery mildew colonies paralleled the progressive branching of mycelia and conidiophore formation. On the resistant cv, PMR-o , however development was arrested at the primary appressorium stage irrespective of the temperature, When the temperature-sensitive resistant line ANC-57 was infected by a race 1 isolate, incubation temperature had a clear effect on the Outcome of the interaction, At 21 degrees, it took longer for symptoms to appear on cv, ANC-57 than on cv. 'Rochet'. while colonies were limited and sparse, At 26 degrees resistance was complete, there being no development.