Effects of Night Temperature and Mist Period on Infection of Sweet Corn byPuccinia sorghi

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Abstract
The effects of mist period and diurnal temperature fluctuation on the development of common rust (Puccinia sorghi) were evaluated on susceptible and partially resistant sweet corn hybrids in growth chambers. The optimal mist period for infection of sweet corn hybrids with P. sorghi was a 12-hr intermittent mist (30 min on/30 min off). A 6-hr constant mist period resulted in significantly fewer, yet abundant, uredinia. Urediniospore germination percentage was not significantly different for the 12-hr 30/30 or 6-hr constant mist periods. These results indicate that the 6-hr constant mist period was sufficient for urediniospore germination but may not have been adequate for complete infection structure formation. Infection was significantly reduced for plants exposed to 0, 3, or 6 hr of 30/30 mist or given a one-time mist with an atomizer. Night temperature appeared to be important in controlling uredinial formation, especially near the critical temperatures of 8 and 32 C. With day temperatures of 24 or 32 C, rust developed most rapidly at night temperatures of 24 and 16 C. Night temperature of 8 C resulted in an extension of the latent period by about 2 days over other treatments. On nights at 32 C, very few uredinia formed, although water-soaked lesions often developed and became necrotic without sporulating.