LOCAL AND MESODISTANCE DISPERSAL OF PYRENOPHORA-TRITICI-REPENTIS CONIDIA

Airborne conidia of Pyrenophora tritici-repentis and environmental con ditions were monitored at Fargo, ND, to infer dispersal distance. In a wheat field after anthesis high numbers of conidia occurred during af ternoon hours after prolonged wetness periods, which confirmed earlier reports on periodicity. Conversely, conidia occurred infrequently whe n the local environment was dry for prolonged periods and diurnal dist ribution lacked a predominant afternoon peak. Samples taken on a rooft op showed that conidia could be found remote from any source. Wheat pl ants in pots became infected by P. tritici-repentis after rooftop expo sure, indicating the presence of viable conidia. Few conidia were foun d early in the season and time of occurrence was not coincident betwee n the roof and field; however, data from the two sampling sites were m ore alike after anthesis. Conidia could have traveled on the order of kilometres to tens of kilometres according to a deterministic forward trajectory model. Based on seasonal pattern, remote occurrence, and th e trajectory model, P. tritici-repentis conidia were dispersed widely (up to 50 km) within the study locale and likely were dispersed mesodi stances (10 to 200 km). Overall, sources of inoculum endogenous to the field released more conidia than exogenous sources but inter-field di spersal may play an important epidemiological role in areas of intensi ve wheat production.