Advances in the characterization of the Pyrenophora tritici-repentis-wheatinteraction

Tan spot of wheat, caused by the fungus Pyrenophora tritici-repentis, is a destructive disease found in wheat-growing regions worldwide that can lead to serious yield losses. Changes in cultural practices have led to an incre ase in the severity and incidence of tan spot. Following infection, compati ble races of the fungus elicit two distinct symptoms in differential wheat lines: tan necrosis and (extensive) chlorosis. Tan necrosis has been clearl y demonstrated by several groups to result from the action of a protein tox in, Ptr ToxA. Wheat sensitivity to this toxin is conditioned by a single do minant gene. The chlorosis response may be more complex and appears to invo lve at least two other toxins, Ptr ToxB and Ptr ToxC, produced by different races of the fungus. Distinct genes apparently condition the reaction of w heat lines to each of these chlorosis-inducing toxins. This review concentr ates on significant advances that have occurred during the past decade in t he characterization of this disease interaction, ranging from the epidemiol ogy and management of tan spot to molecular host-parasite interactions. Par ticular emphasis is placed on work describing fungal race differentiation, production of toxins and their importance in pathogenicity, and the genetic s and physiology of host response to infection.