Impact of continuous or interrupted leaf wetness on infection of chickpea byAscochyta rabiei

Abstract

Ascochyta blight of chickpea increases rapidly under conditions that are too dry for many other foliar pathogens. The impact of leaf wetness (continuous vs. interrupted) and spore density on infection of chickpea by Ascochyta rabiei were investigated under controlled conditions. Disease severity and lesion number increased with increasing wetness period (12, 24, 36, 48, 60, 72 h) and spore density (1, 2, 3, 4, 5 × 10⁵ conidia·mL^–1). The time required for symptom development decreased with increasing wetness period and spore density. Ascochyta blight developed even when inoculated seedlings were subjected to a 24-h interruption in leaf wetness prior to infection. Timing of the drying event had an impact on subsequent disease severity. Disease severity was substantially reduced by a dry period at 2, 4, or 6 h postinoculation, but was affected only slightly by drying after 8 h or more of incubation. Microscopic examination of conidia germinating on leaves showed that the conidia had begun to swell, but had not yet formed germ tubes in the period between 4 and 6 h when they were most vulnerable to drying. The ability of conidia to withstand intermittent dry periods observed in these trials may contribute to the success of the pathogen in the field. An inoculation protocol (20 °C, 48-h wetness period, 2 × 10⁵ conidia·mL^–1) for use in controlled environments was developed as part of this study, and has been used with success in subsequent trials.