Paul P A, Munkvold G P
Department of Plant Pathology, Iowa State University, Ames 50110.
Pioneer Hi-Bred International, Johnston, IA 50131.
Plant Dis. 2005 Jun;89(6):624-630. doi: 10.1094/PD-89-0624.
Controlled environment studies were conducted to determine the effects of temperature on the expansion of lesions of gray leaf spot, and the effects of temperature and relative humidity on the sporulation of Cercospora zeae-maydis on maize (Zea mays). For the lesion expansion experiment, potted maize plants were spray inoculated at growth stage V6, bagged, and incubated at 25 to 28°C and 100% relative humidity for 36 to 40 h. Symptomatic plants were transferred to growth chambers and exposed to constant temperatures of 25, 30, and 35°C. Lesion area (length by width) was measured at 4-day intervals for 17 days. For sporulation studies, lesions were excised from naturally infected maize leaves, measured, and incubated at constant temperature (20, 25, 30, or 35°C) and relative humidity (70, 80, 90, or 100%) for 72 h. Sporulation was estimated as the number of conidia per square centimeter of diseased leaf tissue. A quadratic function was used to model the relationship between log-transformed conidia per square centimeter at 100% relative humidity and temperature. Temperature had a significant effect on lesion expansion (P ≤ 0.05). At 25 and 30°C, the rate of lesion expansion was significantly higher than at 35°C (P ≤ 0.05). The largest lesions and the highest mean rate of lesion expansion were observed at 30°C; however, the mean lesion expansion rate at this temperature was not significantly different from that at 25°C. The interaction effect of temperature and relative humidity on the log of conidia per square centimeter of diseased tissue was significant (P ≤ 0.05). At 100% relative humidity, the effect of temperature on sporulation was significant (P ≤ 0.05), with maximum spore production occurring at 25 and 30°C. The quadratic model explained between 49 and 80% of the variation in the log of conidia per square centimeter at 100% with variation in temperature. These results suggest that the rapid increase in gray leaf spot severity generally observed during mid- and late summer may be due to favorable conditions for lesion expansion during this period. When relative humidity is >95%, expanding lesions may serve as a source of inoculum for secondary infections.
进行了控制环境研究，以确定温度对玉米灰斑病病斑扩展的影响，以及温度和相对湿度对玉米尾孢菌在玉米（Zea mays）上产孢的影响。对于病斑扩展实验，在V6生长阶段对盆栽玉米植株进行喷雾接种，套袋，并在25至28°C和100%相对湿度下培养36至40小时。有症状的植株转移到生长室，暴露于25、30和35°C的恒定温度下。每隔4天测量病斑面积（长×宽），持续17天。对于产孢研究，从自然感染的玉米叶片上切下病斑，测量后在恒定温度（20、25、30或35°C）和相对湿度（70、80、90或100%）下培养72小时。产孢量以每平方厘米病叶组织上的分生孢子数来估计。使用二次函数来模拟在100%相对湿度下每平方厘米经对数转换的分生孢子数与温度之间的关系。温度对病斑扩展有显著影响（P≤0.05）。在25和30°C时，病斑扩展速率显著高于35°C（P≤0.05）。在30°C时观察到最大的病斑和最高的平均病斑扩展速率；然而，该温度下的平均病斑扩展速率与25°C时无显著差异。温度和相对湿度对每平方厘米病组织上分生孢子对数的交互作用显著（P≤0.05）。在100%相对湿度下，温度对产孢有显著影响（P≤0.05），在25和30°C时产孢量最大。二次模型解释了在100%相对湿度下每平方厘米分生孢子对数随温度变化的49%至80%的变异。这些结果表明，在夏中晚期通常观察到的玉米灰斑病严重程度的快速增加可能是由于在此期间有利于病斑扩展的条件。当相对湿度>95%时，扩展的病斑可能成为二次感染的接种源。
