The role of conidia in the dispersal of Ascochyta rabiei

Ascochyta rabieiasexual spores (conidia) were assumed to spread over short distances (similar to 10 m) in a combination of rain and strong wind. The potential distance of conidial spread was investigated in three rainfall and three sprinkler irrigation events. Chickpea trap plants were distributed at the distances of 0, 10, 25, 50 and 75 m from infected chickpea plots before scheduled irrigation and forecast rainfall events. Trap plants were transferred to a controlled temperature room (20 degrees C) for 48 h (100% humidity) after being exposed in the field for 2-6 days for rainfall events, and for 1 day for irrigation events. After a 48 h incubation period, trap plants were transferred to a glasshouse (20 degrees C) to allow lesion development. Lesions on all plant parts were counted after 2 weeks, which gave an estimate of the number of conidia released and the distance travelled. Trap plants at all distances were infected in all sprinkler irrigation and rainfall events. The highest number of lesions on trap plants were recorded closest to the infected plots -the numbers decreased as the distance from the infected plots increased. There was a significant (p < 0.05) relationship between the amount of rainfall and the number of lesions recorded. A generalised additive model was developed that efficiently described spatial patterns of conidial spread. With further development, the model can be used to predict the spread ofA. rabiei. This is the first systematic study to show that conidia distributeA. rabieiover longer distances than previously reported.