Arauz L F, Neufeld K N, Lloyd A L, Ojiambo P S
Department of Plant Pathology, North Carrolina State University, Raleigh, NC 27695, USA.
Phytopathology. 2010 Sep;100(9):959-67. doi: 10.1094/PHYTO-100-9-0959.
The influence of temperature and leaf wetness duration on germination of sporangia and infection of cantaloupe leaves by Pseudoperonospora cubensis was examined in three independent controlled-environment experiments by inoculating plants with a spore suspension and exposing them to a range of leaf wetness durations (2 to 24 h) at six fixed temperatures (5 to 30 degrees C). Germination of sporangia was assessed at the end of each wetness period and infection was evaluated from assessments of disease severity 5 days after inoculation. Three response surface models based on modified forms of the Weibull function were evaluated for their ability to describe germination of sporangia and infection in response to temperature and leaf wetness duration. The models estimated 15.7 to 17.3 and 19.5 to 21.7 degrees C as the optimum temperature (t) range for germination and infection, respectively, with little germination or infection at 5 or 30 degrees C. For wetness periods of 4 to 8 h, a distinct optimum for infection was observed at t = 20 degrees C but broader optimum curves resulted from wetness periods >8 h. Model 1 of the form f(w,t) = f(t) x (1 - exp{-B x w}) resulted in smaller asymptotic standard errors and yielded higher correlations between observed and predicted germination and infection data than either model 2 of the form f(w,t) = A{1 - exp- f(t) x (w - C)} or model 3 of the form f(w,t) = [1 - exp{-(B x w)(2)}]/cosh[(t - F)G/2]. Models 1 and 2 had nonsignificant lack-of-fit test statistics for both germination and infection data, whereas a lack-of-fit test was significant for model 3. The models accounted for approximately 87% (model 3) to 98% (model 1) of the total variation in the germination and infection data. In the validation of the models using data generated with a different isolate of P. cubensis, slopes of the regression line between observed and predicted germination and infection data were not significantly different (P > 0.2487) and correlation coefficients between observed and predicted values were high (r(2) > 0.81). Models 1 and 2 were used to construct risk threshold charts that can be used to estimate the potential risk for infection based on observed or forecasted temperature and leaf wetness duration.
在三个独立的可控环境实验中，通过用孢子悬浮液接种植株，并将其置于六个固定温度（5至30摄氏度）下的一系列叶片湿润持续时间（2至24小时）中，研究了温度和叶片湿润持续时间对古巴假霜霉游动孢子囊萌发及甜瓜叶片感染的影响。在每个湿润期结束时评估游动孢子囊的萌发情况，并在接种后5天通过评估病害严重程度来评价感染情况。评估了基于威布尔函数修正形式的三个响应面模型描述游动孢子囊萌发及感染对温度和叶片湿润持续时间响应的能力。模型估计萌发和感染的最适温度（t）范围分别为15.7至17.3摄氏度和19.5至21.7摄氏度，在5或30摄氏度时几乎没有萌发或感染。对于4至8小时的湿润期，在t = 20摄氏度时观察到明显的感染最适温度，但湿润持续时间>8小时时得到更宽的最适曲线。形式为f(w,t) = f(t) x (1 - exp{-B x w})的模型1产生的渐近标准误差较小，并且与形式为f(w,t) = A{1 - exp- f(t) x (w - C)}的模型2或形式为f(w,t) = [1 - exp{-(B x w)(2)}]/cosh[(t - F)G/2]的模型3相比，在观察到的和预测的萌发及感染数据之间产生了更高的相关性。模型1和2对萌发和感染数据的失拟检验统计量均不显著，而模型3的失拟检验显著。这些模型解释了萌发和感染数据总变异的约87%（模型3）至98%（模型1）。在使用来自不同古巴假霜霉菌株产生的数据对模型进行验证时，观察到的和预测的萌发及感染数据之间的回归线斜率无显著差异（P > 0.2487），且观察值与预测值之间的相关系数较高（r(2) > 0.81）。模型1和2用于构建风险阈值图表，可用于根据观察到的或预测的温度和叶片湿润持续时间估计感染的潜在风险。
