Influence of Temperature and Light on Severity of Bacterial Blight of Corn, Oats, and Wheat

Abstract

SCHAAD, N. W., D. R. SUMNER, and G. 0. WARE. 1980. Influence of temperature and light on severity of bacterial blight of corn, oats, and wheat. Plant Disease 64:481-483. Two experiments using five strains of Pseudomonas avenae and five day/night temperature regimens were conducted to determine the influence of temperature and light on the severity of bacterial leaf blight of corn, wheat, and oats. The first experiment showed that light had no effect on lesion development. In the second experiment, plant growth data for corn and wheat were recorded also. The effects of temperature on blight severity differed with the host. On corn, lesion development was not affected by temperature but plant growth was significantly reduced at the three intermediate temperature regimens. Average lesion size was significantly greater with strain C-71 than with strain 19860 at temperatures of 22/ 14 and 18/14 C but not at 30/ 26, 30/22, or 22/18 C. On oats, P. avenae strain significantly affected lesion development and disease was generally more severe at higher temperatures. On wheat, blight symptoms were generally more severe at higher temperatures but P. avenae strain had no significant effect. Under Georgia conditions, bacterial blight should be less severe in oats and wheat sown late in the fall season when the temperature is cooler. With corn, plant growth should be less reduced when the mean evening temperature is > 22 C. Strains of P. avenae should affect the severity of bacterial leaf blight of corn and oats but not of wheat. Bacterial leaf blight of corn, caused by Pseudomonas avenae (4), has been observed sporadically in corn fields in southern Georgia for several years. Severe outbreaks generally occur in late May and early June after periods of overcast and wet weather (7). Mean temperatures in south Georgia during this period are usually 18-24 C (7). The first symptoms are usually observed in early May when corn plants are 0.8-1 m tall. Although bacterial leaf blight of corn has been known for many years (2,8), little information is available on the effects of light and temperature on disease severity. Johnson et al (2) observed in a greenhouse that symptoms were abundant at 29-35 C, few at 24 C, and infrequent or lacking at 21 C. There are no reports of any observations on the effects of temperature on disease severity in oats and wheat. The objective of our study was to determine the influence of temperature and light on the severity of bacterial blight of corn, oats, and wheat. We wanted to determine if temperature and/ or light could also be used to predict disease occurrence. Experiments were done in environ