Banana black leaf streak disease (Mycosphaerella fijiensis) in Western Samoa

The morphology of M. fijiensis and the pattern of sympton development in Western Samoa was similar to that found elsewhere. Rain, as little as 0.25 mm, was more important than dew in releasing ascospores of M. fijiensis from leaf tissue. In the laboratory ascospore release started within 10–15 min of wetting leaves and most spores were discharged within 3 h. When leaves were wetted on successive days more spores were released but the effect on total spore production was not determined. The midrib spotting infection pattern appeared to be caused by ascospore infections and could be simulated under defined conditions by weedkiller sprays. The tip spotting pattern found on most leaves in Samoan banana plantations indicated that ascospores were the major source of inoculum. Percentage germination, germ-tube growth, number of germ tubes and location of germ tubes on both ascospores and conidia were significantly affected by temperature, type of substrate and moisture.