VIEW ARTICLE

Ecology and Epidemiology

Influence of Temperature, Wetness Period, Plant Age, and Inoculum Concentration on Infection and Development of Ascochyta Blight of Chickpea. A. Trapero -Casas, Former visiting scientist, USDA Agricultural Research Service, Western Regional Plant Introduction Station, Washington State University, Pullman 99164-6402, Present address: Departamento de Agronomía, ETSIAM, Universidad de Córdoba, Apartado 3048, 14080 Córdoba, Spain; W. J. Kaiser, Research plant pathologist, USDA Agricultural Research Service, Western Regional Plant Introduction Station, Washington State University, Pullman 99164-6402. Phytopathology 82:589-596. Accepted for publication 6 January 1992. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1992. DOI: 10.1094/Phyto-82-589.

The optimum temperature for infection and development of Ascochyta blight of chickpea, caused by Ascochyta rabiei, in 2-wk-old seedlings in controlled environment studies was about 20 C. At this temperature, 7.6 and 17 h of wetness were required for the pathogen to cause significant light and severe infection, respectively. Increasing wetness periods greater than 6 h during the infection period resulted in increased disease severity, regardless of the temperature. Some infection (9.6%) occurred even when plants did not receive a wetting period after inoculation. Dry periods (6–48 h) immediately after inoculation increased disease severity over plants receiving the same wetness period without drying, while the opposite effect occurred when dry periods >12 h were initiated after an initial wetting period of 6 h. Although disease development and symptom expression were most affected by temperature during infection, postinfection temperature also was influential. The lower and upper limits for infection and disease development were < 5 and about 30 C, respectively. Disease development was suppressed at 30 C in plants incubated at 20 C during the infection period. At a constant temperature of 20 C, the minimum incubation and latent periods were 4.5 and 5.5 days, respectively. Lower or higher temperatures increased the duration of these periods. Disease developed more slowly in 8-wk-old plants at the podding stage than in 2-wk-old seedlings, but final disease severity in both groups of plants was similar for most temperatures. Increasing inoculum concentration from 4 × 10⁴ to 1 × 10⁷ conidia per milliliter increased disease severity, the magnitude of which depended on the level of resistance of the chickpea cultivars to blight. A multiple regression model was derived empirically to describe disease severity 14 days after inoculation as a function of temperature and wetness duration. Other models were developed to describe the duration of wetness period for a specified level of disease, incubation period, latent period, and disease development as functions of temperature.