USE OF OOSPORES AS INOCULUM FOR EARLY-STAGE RESISTANCE SCREENING FOR DOWNY MILDEW AND PACHYMETRA ROOT ROT

EARLY-STAGE disease resistance screening potentially offers an efficient method for selecting high-yielding disease-resistant varieties for commercial sugarcane production, especially for those diseases that limit productivity across an industry. Oospores are a long-lasting, resistant spore produced by oomycetes; their use as inoculum is routine for latter-stage Pachymetra root rot resistance screening trials but has rarely been attempted for sugarcane downy mildew (DM). Oospores were used in early-stage resistance screening tests for both diseases; spores were mixed with soil / potting mix and original seedlings / single eye setts planted into the infested material. Original seedlings were not unduly affected by Pachymetra root rot, with seedling death largely absent. On the other hand, a large proportion of plants of a susceptible variety growing from single-eye setts planted in DM-infested soil became infected by DM. The technique offers promise for early-stage DM resistance screening; on the other hand, early screening of original seedlings for Pachymetra resistance using oospores is unlikely to be successful. The downy mildew technique will be refined further to ensure good discrimination of resistance in test varieties. Other forms of early-stage resistance screening will be examined for Pachymetra root rot.