Simulated soil and plant management effects on root rots of subterranean clover

Abstract

Pasture productivity in southern Australia is often limited by root diseases of complex etiology. The influences of simulated plant and soil management procedures on subterranean clover (Trifolium subterranean cv. Woogenellup) root rots were evaluated in controlled environments, using a soil from an irrigated and from a dryland pasture. Root rot incidence and severity were high in soils collected and used as intact cores, and low to moderate in soils disturbed while being collected. Simulated cultivation of soil in cores also reduced root rots in the dryland pasture soil that had little surface litter, but not in the irrigated pasture soil which had high levels of organic debris (and pathogen inocula) distributed through the surface 0-11 cm. Root rot was mild on plants in continually moist cores at 10¦C, and severe in cyclically wetted and dried cores at 10, 15 and 20¦C, and in continually moist cores at 15 and 20¦C. Root rots were reduced by treatment of seeds with Rhizobium, fungicides, or both, by drenching soils with fungicides, and by planting the resistant T. yanninicum cvv. Larisa, Meteora and Trikkala. Removal of seedling leaves, to simulate grazing, accentuated root rot severity. The identified pathogens included species of Pythium, Fusarium, Rhizoctonia, and nematodes. Integrated strategies for controlling root rots of subterranean clover are considered promising in view of these studies with cores of pasture soils.