Evidence for a heterothallic mating system in Tapesia acuformis using benomyl sensitivity and esterase isoenzyme profiles

Abstract

Ascospore progenies from eight apothecia of Tapesia sp., collected from wheat stubble in Belgium and Germany, yielded strains characteristic of T. acuformis and strains characteristic of T. yallundae. The colony and conidium morphology, esterase isoenzyme profiles and sensitivity to benomyl, diethofencarb and triadimenol of these and of isolates from eyespot lesions were compared. Differences were detected amongst the ascospore offspring from single apothecia using these markers, but all strains from a single apothecium were always of a single species of Tapesia. Single-ascospore strains from a single ascus could always be grouped into four pairs using a combination of markers. In vitro pairwise crossings between four representative single-ascospore strains of T. acuformis yielded some mature and fertile apothecia on moist wheat straw inoculated with mycelium and incubated in test tubes under a mixture of nuv light and daylight at 8-12 degrees C for at least 6 months. Recombination was observed between the parental esterase zymograms and sensitivities to benomyl, leading to new phenotypes in the progeny. The results of pairing reference single-ascospore strains of both T. acuformis and T. yallundae with 115 isolates from eyespot lesions strengthened the contention that T. acuformis exhibits a two-allele heterothallism and that T. acuformis and T. yallundae are sexually incompatible species.