Symptom expression of Phytophthora colocasiae in inoculated taro corms

Abstract

Taro leaf blight (TLB), caused by Phytophthora colocasiae, is normally characterised by leaf lesions. There are isolated reports of P. colocasiae causing a corm rot but the symptoms are not well defined and have not been recorded in Samoa. Here we report on an inoculation method and describe the symptoms of corm rot caused by P. colocasiae. In this study, a corm inoculation method was developed in physical containment laboratories in New Zealand and subsequent symptom development studies were undertaken on TLB-tolerant taro cultivars in Apia, Samoa. The Samoan TLB-tolerant taro cultivars were able to be wound-infected with P. colocasiae and the results confirm previous descriptions of P. colocasiae infection giving rise to light brown firm rots in corms. This work has allowed the pictorial record of corm rots to be updated, potentially providing for better distinction between corm rots caused by P. colocasiae and those caused by other pathogens, such as Fusarium spp.