Phytopathology. 2002 Jun;92(6):631-6. doi: 10.1094/PHYTO.2002.92.6.631.
ABSTRACT The effect of temperature on infection of lettuce by Bremia lactucae was investigated in controlled environment studies and in the field. In controlled conditions, lettuce seedlings inoculated with B. lactucae were incubated at 15, 20, 25, or 30 degrees C during a 4-h wet period immediately after inoculation or at the same temperatures during an 8-h dry period after the 4-h postinoculation wet period at 15 degrees C. High temperatures during wet and dry periods reduced subsequent disease incidence. Historical data from field studies in 1991 and 1992, in which days with or without infection had been identified, were analyzed by comparing average air temperatures during 0600 to 1000 and 1000 to 1400 Pacific standard time (PST) between the two groups of days. Days without infection had significantly higher temperatures (mean 21.4 degrees C) than days with infection (20.3 degrees C) during 1000 to 1400 PST (P < 0.01) but not during 0600 to 1000 PST. Therefore, temperature thresholds of 20 and 22 degrees C for the 3-h wet period after sunrise and the subsequent 4-h postpenetration period, respectively, were added to a previously developed disease warning system that predicts infection when morning leaf wetness lasts >/=4 h from 0600 PST. No infection was assumed to occur if average temperature during these periods exceeded the thresholds. Based on nonlinear regression and receiver operating characteristic curve analysis, the leaf wetness threshold of the previous warning system was also modified to >/=3-h leaf wetness (>/=0900 PST). Furthermore, by comparing solar radiation on days with infection and without infection, we determined that high solar radiation during 0500 to 0600 PST in conjunction with leaf wetness ending between 0900 and 1000 PST was associated with downy mildew infection. Therefore, instead of starting at 0600 PST, the calculation of the 3-h morning leaf wetness period was modified to start after sunrise, defined as the hour when measured solar radiation exceeded 8 W m(-2) (or 41 mumol m(-2) s(-1) for photon flux density). The modified warning system was compared with the previously developed system using historical weather and downy mildew data collected in coastal California. The modified system was more conservative when disease potential was high and recommended fewer fungicide applications when conditions were not conducive to downy mildew development.
摘要 在控制环境和田间条件下研究了温度对莴苣霜霉病感染的影响。在控制条件下，将接种了霜霉病菌的莴苣幼苗在接种后 4 小时的湿润期内于 15、20、25 或 30°C 下孵育，或在 15°C 下在接种后 4 小时的湿润期后 8 小时的干燥期内于相同温度下孵育。湿期和干期的高温降低了随后的发病率。对 1991 年和 1992 年田间研究的历史数据进行了分析，这些数据确定了有感染和无感染的天数，通过比较两组天数的太平洋标准时间（PST）0600 至 1000 和 1000 至 1400 之间的平均空气温度来进行分析。无感染天数的温度（平均 21.4°C）明显高于感染天数（20.3°C）（PST 1000 至 1400）（P <0.01），但在 PST 0600 至 1000 期间并非如此。因此，在日出后 3 小时的湿润期和随后的 4 小时穿透期，分别添加了 20 和 22°C 的温度阈值，以补充先前开发的疾病预警系统，该系统预测当早晨叶片湿润持续时间> = 4 小时时发生感染。如果这些时期的平均温度超过阈值，则假设不会发生感染。基于非线性回归和接收者操作特征曲线分析，还修改了先前预警系统的叶片湿润阈值，以> = 3 小时叶片湿润（> = 0900 PST）。此外，通过比较有感染和无感染天数的太阳辐射，我们确定在 PST 0500 至 0600 期间的高太阳辐射与 PST 0900 至 1000 之间结束的叶片湿润相结合与霜霉病感染有关。因此，代替从 PST 0600 开始，将早晨 3 小时叶片湿润期的计算修改为日出后开始，定义为测量的太阳辐射超过 8 W m（-2）（或光子通量密度的 41 mumol m（-2）s（-1））的小时。使用加利福尼亚沿海收集的历史天气和霜霉病数据，将修改后的预警系统与先前开发的系统进行了比较。当疾病潜力较高时，修改后的系统更为保守，并且当不利于霜霉病发展的条件下，推荐使用较少的杀菌剂。
