Effects of Temperature and Wetness Duration on Infection of Peanut Cultivars by Cercospora arachidicola

Abstract

The effects of temperature and duration of wetness (relative humidity >/=95%) on infection of three peanut cultivars by Cercospora arachidicola were determined under controlled conditions. Plants of the Spanish cv. Spanco and the runner cvs. Florunner and Okrun were exposed to constant temperatures of 18 to 30 degrees C during 12-h periods of wetness each day that totaled 12 to 84 h following inoculation of leaves with conidia. Severity of disease, measured by either lesion density (number per leaf) or lesion size (diameter), was greatest for 'Spanco', intermediate for 'Florunner', and lowest for 'Okrun' in each of two experiments. Lesion density was evaluated further because it was an indicator of both the occurrence and degree of infection. Nonlinear regression analysis was employed to evaluate the combined effects of temperature (T) and wetness duration (W) on lesion density (Y). In the regression model, the Weibull function characterized the monotonic increase of Y with respect to W, while a hyperbolic function characterized the unimodal response of Y with respect to T. Parameters for the intrinsic rate of change with respect to W (b), the intrinsic rate of change with respect to T (f), the optimal value of T (g), and the upper limit (e) when T is optimum (T = g) were estimated for each cultivar and experiment. The effect of cultivar was characterized primarily by differences in the upper limit parameter e. In each experiment, e was greatest for 'Spanco', intermediate for 'Florunner', and least for 'Okrun'. The effect of cultivar on b followed a pattern similar to that for e in experiment 1, but not in experiment 2. Differences among cultivars for estimates of f and g were small and inconsistent. Estimates for g were precise for each cultivar and experiment and fell within the range of 22.3 to 23.2 degrees C. Cultivar responses to T and W were further evaluated using data pooled over the two experiments. Parameter e was estimated for each cultivar, but common values of b, f, and g were estimated. At e = 22.8 degrees C, lesion density approached an upper limit of 96, 17, and 6 lesions per leaf for the cvs. Spanco, Florunner, and Okrun, respectively. These fitted values approximated the observed values of 86, 25, and 9 lesions per leaf for the respective cultivars. Cultivars varied in their response to W at a given T. At 22.8 degrees C, one lesion per leaf was expected following 26, 30, and 36 h of wetness for 'Spanco', 'Florunner', and 'Okrun', respectively. If temperature was increased to 28 degrees C, one lesion per leaf was expected following 36, 44, and 54 h of wetness for the respective cultivars.

Effect of Various Factors on the Development of Leaf Spot Disease in Mulberry

“…It was reported that air relative humidity >95% or leaf wetness was required for Cercospora infection and subsequent lesion development in sugar beet (Wolf and Verreet, 2005). The effect of temperature and duration of wetness on infection of three peanut cultivars by Cercospora arachidicola was reported (Wu et al, 1999). Alderman and Beute (Alderman and Beute, 1986) reported that conidia of Cercospora require a saturated atmosphere to germinate at optimum temperatures of 16 to 25 ºC.…”

Weather-based Pest Forecasting for Efficient Crop Protection

“…In some studies, individual computer programs have been developed based on various weather parameters to make predictions, while others studies have incorporated computer programs into commercial advisory equipment (Cu and Phipps, 1993;Grichar et al, 2005;Boyle, 1965, 1966;Linvill and Drye, 1995;Parvin et al, 1974;Shew et al, 1988;Wu et al, 1999).…”

“…In addition to temperature and precipitation, relative humidity is another weather variable that has been shown in many studies to be related to the development of fungal pathogens (Damicone et al, 1994;Boyle, 1965, 1966;Jewell, 1987;Olatinwo et al, 2008Olatinwo et al, , 2009Olatinwo et al, , 2011Shew et al, 1988;Wu et al, 1999). In monitoring the likelihood of infection initiation through sporulation of fungal spores, the available moisture on a leaf surface can be estimated using relative humidity, since it correlates with wetness of a leaf surface within a canopy.…”

“…Monitoring environmental conditions such as rainfall, relative humidity, leaf surface wetness, and temperature to optimize pesticide applications is critical for reducing infection initiation and disease development (Alderman and Beute, 1986;Boyle, 1965, 1966;Shew et al, 1988;Wu et al, 1999). Although chemical pesticides are effective tools for managing diseases and pests, they can be inefficient methods for managing pests due to unintended negative impacts on the ecosystems.…”

“…Therefore, timely and effective management of the disease rely on good monitoring of environmental conditions, i.e. rainfall, relative humidity, leaf wetness, and temperature, which are required for infection to occur (Alderman and Beute, 1986;Boyle, 1965, 1966;Shew et al, 1988;Wu et al, 1999).…”