Effects of light, temperature, and leaf wetness duration on daylily rust

Experiments in controlled environments were completed to determine the influence of light intensity, temperature, and leaf wetness duration on daylily rust caused by Puccinia hemerocallidis. As light intensity increased, there was a significant decrease in urediniospore germination (R-2 = 0.88 and Y = 96-0.6x). Urediniospores germinated in vitro between 7 and 34 C with an optimal temperature of 22 to 24degreesC. To test the effect of temperature on infection efficiency, plants were inoculated with urediniospores, incubated under high relative humidity at 4, 10, 22, 30, or 36degreesC, and then transferred to a greenhouse at 23 C for 15 day. Plants incubated at 22degreesC had an average of 13 lesions cm leaf(-1). Incubation temperatures of 4, 10, 30, or 36degreesC resulted in less than 1.5 lesions cm leaf(-1). Plants were inoculated, incubated at 22degreesC for 24 h, and then incubated at different temperatures for 15 days to test the effect of temperature on disease development. There were no significant differences in disease development at 22 and 30degreesC; however, there were significantly fewer lesions at 10degreesC and no lesions developed at 36degreesC within 15 days. Five to six h of leaf wetness were required for lesion development and as the duration of leaf wetness increased, there was a significant increase in the number of lesions that developed. These studies indicate that for disease development of P. hemerocallidis on daylily, temperatures around 22degreesC and 5 h of leaf wetness are required during infection. However, once a daylily is infected, disease development is not as sensitive to environmental conditions.