Cashew leaf and nut blight – a new disease of cashew in Tanzania caused by Cryptosporiopsis spp

Abstract

In August 2002, a new and damaging leaf and nut blight disease was observed on young tissues of cashew (Anacardium occidentale) in southern Tanzania. Angular lesions, and dark tan with a dark reddish brown margin were formed on leaves, often vein-limited and containing conidiomata. Lesions subsequently enlarged and coalesced, causing blighting and defoliation. Older lesions became papery and silver/grey in colour and developed shot-holes. During fruit setting, infection of young nuts caused rapid blackening and abscission, resulting in significant yield losses. Infection of older nuts resulted in a characteristic dark, slightly sunken 'tar spot'-like lesion. Diseased plant materials were sent to the Global Plant Clinic in October 2003, where a new and undescribed Cryptosporiopsis species was consistently isolated from the nut and leaf lesions. Wounded and non-wounded leaves of cashew were inoculated with an aqueous conidial suspension (1×106 conidia/ml) or with water (control) and maintained at 24-28°C and 95% RH for 24 h. All inoculated plants showed leaf lesions similar to that observed in the field within 7-10 days after inoculation. None of the control plants developed any symptoms. A Cryptosporiopsis species was reisolated that was morphologically identical to the original isolate inoculated. This is thought to be the first report of this genus attacking cashew