Phenology of Didymella rabiei Development on Chickpea Debris Under Field Conditions in Spain

ABSTRACT The development of Didymella rabiei on debris of naturally infected chickpea was investigated in four chickpea-growing areas with different climatic conditions in Spain during 1987 to 1992. D. rabiei extensively colonized chickpea debris and formed pseudothecia and pycnidia. Differentiation of pseudothecial initials occurred regularly across experimental locations by November, 1 month after placement of debris on the soil. Ascospore maturation occurred mainly from late January to late March, depending on location and year. Maximum ascospore discharge from sampled debris pieces placed under suitable environmental conditions occurred 2 to 4 weeks after ascospore maturation, after which ascospore release decreased sharply. Pseudothecia were exhausted, due to ascospore discharge, by the beginning of summer. New asci did not develop in empty pseudothecia and no pseudothecia formed in tissues after the first season. Ascospore maturation and liberation in cooler locations were more uniform and occurred later compared to maturation in warmer locations. Also, production of asci and ascospores per pseudothecium was much higher in cooler than in warmer locations. A similar relationship was found for density of pseudothecia and pycnidia and conidia production per pycnidium. The percentage of mature pseudothecia increased according to the logistic model, with the cumulative number of Celsius degree days calculated by computing the mean of the maximum and minimum daily air temperatures on rainy days from the date of debris placement on the soil. There were significant differences among model parameter estimates between cooler and warmer locations, but minor differences were found among parameters for locations with similar environmental conditions. There was an inverse linear relationship between the average temperature during the period of pseudothecia maturation and the number of asci produced per pseudothecium.