ARS | Publication request: Release of Didymella rabiei ascospores from infested chickpea debris in relation to weather variables in the Pacific Northwest of the USA.

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: July 20, 2006
Publication Date: July 28, 2006
Citation: Chilvers, M., Peever, T., Akamatsu, H., Chen, W., Muehlbauer, F.J., Alldredge, R. 2006. Release of Didymella rabiei ascospores from infested chickpea debris in relation to weather variables in the Pacific Northwest of the USA. Phytopathology 96:S23.

Technical Abstract: Didymella rabiei (anamorph: Ascochyta rabiei), the fungus that causes Ascochyta blight of chickpea, produces pseudothecia on overwintered chickpea debris. Ascospores are thought to constitute an important primary inoculum source for Ascochyta blight epidemics in the US-Pacific Northwest. The timing of ascospore release in the field was investigated using potted highly susceptible chickpea plants. In the fall, chickpea debris, heavily infected with A. rabiei, was spread in a 1 m(^2) area, 5 cm deep, secured with netting and allowed to overwinter. Nine pots of 2-week old trap plants were placed at a distance of 1m from the debris. Following exposure of trap plants in the field for 2–3 days, they were returned to the greenhouse, misted with water and covered to maintain leaf wetness for 24h. Ascochyta lesions were counted 2 weeks later with each lesion assumed to represent a single ascospore. The experiment was repeated over two years and was replicated at two sites. Ascospore release began in mid-March, coinciding with the maturity of pseudothecia and continued through the beginning of June when numbers of trapped ascospores dropped off dramatically. We observed a correlation of ascospore release with rainfall events. We have developed a simple model for predicting ascospore release from overwintered debris, which will assist growers with disease management decisions.