Impact of glandular hair exudates on infection of chickpea by Ascochyta rabiei

Abstract

Ascochyta blight, a fungal disease caused by Ascochyta rabiei (Pass.) Labr. (teleomorph Didymella rabiei (Kovačevski) v. Arx), is a major constraint to chickpea (Cicer arietinum L.) production. An unusual feature of chickpea plants is the secretion of a highly acidic fluid from glandular trichomes. This exudate was shown to promote germination of conidia of A. rabiei at low concentrations (0.012 and 0.06 mg·mL–1) but to inhibit germination at higher concentrations (0.3 and 1.5 mg·mL–1). The removal of exudates from plants prior to inoculation with A. rabiei increased infection and, subsequently, disease development in susceptible cultivars. On partially resistant cultivars, however, the effect of removing exudates on infection was not apparent until early podding, when genetic resistance declines. Simulated rain applied prior to inoculation increased disease severity as the volume of simulated rain increased from 1 to 4 mm. Since rainfall is required for dispersal of conidia, host exudates are likely to have little impact on secondary disease spread under field conditions. Exudates may, however, contribute to variability in disease studies conducted on older chickpea plants, especially in controlled environments.Key words: ascochyta blight, epidemiology, screening, Didymella rabiei, Cicer arietinum.