Etiology of Root and Stalk Rots of Maize in North Queensland. Disease Development and Associated Fungi.

Abstract

The etiology and development of mesocotyl, root and stalk rots of maize on the Atherton Tableland in north Queensland were investigated in two seasons. The identities and relative isolation frequencies of fungi from the mesocotyls, roots and stalks were determined at different stages of growth at two sites. Mesocotyl rot was first observed ca. 40 days after planting, and by ca. 80 days most of the mesocotyls and seminal roots were dead. Trichoderma spp., Penicillium spp., Pyrenochaeta indica, Fusarium moniliforme and F. oxysporum were isolated most frequently from the mesocotyls. Maize root rot developed in two distinct phases, in the first phase, it was independent of stalk rot and occurred on the lower nodal roots during vegetative growth from ca. 40 days. P. indica, recorded for the first time on maize, was the major fungus isolated from root lesions before maturity (ca. 130 days) but was uncommon thereafter. The second phase developed after physiological maturity and was associated with senescence and stalk rot. Fusarium graminearum, F. moniliforme and F. oxysporum prevailed at this stage. Stalk rot developed after physiological maturity and was most severe at the wetter site where pathogens caused severe defoliation and harvest was delayed by high humidity. A sequence of fungi occurred in maize stalks; Colletotrichum graminicola was prevalent immediately after maturity, while F. graminearum and F. moniliforme predominated at harvest.