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Blackleg Sporacle: A Model for Predicting Onset of Pseudothecia Maturity and Seasonal Ascospore Showers in Relation to Blackleg of Canola

September 2003 , Volume 93 , Number  9
Pages  1,073 - 1,081

M. U. Salam , R. K. Khangura , A. J. Diggle , and M. J. Barbetti

First author: Centre for Cropping Systems, Department of Agriculture-Western Australia, Lot 12 (P.O. Box 483), Northam, WA 6401, Australia; second, third, and fourth authors: Department of Agriculture-Western Australia, 3 Baron-Hay Court, South Perth, WA 6151, Australia; and third and fourth authors: Co-operative Research Centre for Legumes in Mediterranean Agriculture and Soil Science Discipline, School of Earth and Geographical Sciences, University of Western Australia, Crawley, WA 6009, Australia

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Accepted for publication 22 March 2003.

A simple model has been developed to predict the onset of pseudothecia maturity and seasonal ascospore showers in relation to blackleg disease in canola, caused by the fungus Leptosphaeria maculans. The model considers a combination of two weather factors, daily mean temperature and daily total rainfall, to drive progress of maturity of pseudothecia on the infested canola stubble left from past crops. Each day is categorized as suitable or not suitable for progress of the maturation process. The onset of pseudothecia maturity occurs when approximately 43 suitable days have occurred. Following the onset of maturity, ascospore showers are triggered when daily rainfall exceeds a threshold. The model satisfactorily predicted the timing of the onset of pseudothecia maturity when tested with 3 years of field observations at four locations in Western Australia, which characteristically has a Mediterranean climate. The model also agreed reasonably well with the daily pattern of ascospore release observed in two locations. Sensitivity analysis was performed to show the relative importance of the parameters that describe the onset of pseudothecia maturity.

Additional keywords: ascospore discharge, oilseed rape, Phoma lingam , stem canker.

© 2003 The American Phytopathological Society