SURVIVAL OF WHEAT PATHOGENS IN WHEAT AND SOYBEAN RESIDUES UNDER CONSERVATION TILLAGE SYSTEMS IN SOUTHERN AND CENTRAL BRAZIL

The incidence of the wheat pathogens Gibberella zeae, Cochliobolus sativus, and Leptosphaeria nodorum. was determined in wheat and soybean residues collected from the soil surface of plots under conservation tillage in southern and central Brazil. In addition, the inoculum density of the first two fungi was assessed after incubation of residues at high humidity. The incidence of the pathogens varied among and within locations and between plant species. With one exception, the fungi were isolated less frequently from soybean than from wheat residues. In soybean residues, G. zeae was much more prevalent than C. sativus or L. nodorum. Inoculum density of C. sativus exceeded that of G. zeae on wheat residues and was much greater on wheat than on soybeann residues. The crop rotation history of the plots did not markedly affect the incidence of fungi from residues of wheat or soybean. The possible mechanism of colonization of soybean plants by the wheat pathogens is discussed.