EFFECT OF WETTING-PERIOD DURATION ON ASCOCARP SUPPRESSION BY SELECTEDANTAGONISTIC FUNGI IN WHEAT-STRAW INFESTED WITH PYRENOPHORA-TRITICI-REPENTIS

Wheat straw axenically or naturally infested with Pyrenophora tritici- repentis was inoculated with one of several antagonistic fungi and exp osed to various treatments of alternate wetting and drying, and ascoca rp production by P. tritici-repentis on straw was measured. Wetting tr eatments were repeated wet periods of 6, 12, 24, or 48 h separated by drying periods. In the absence of suppressive fungi, ascocarp formatio n by P. tritici-repentis was observed in both axenically colonized str aw and naturally infested field straw in all wetting treatments, and t he effect of wetting duration on ascocarp formation was not obvious. S uppression of ascocarp formation in both field and axenic straw by sel ected antagonistic fungi was affected by the duration of intermittent wetting. In field straw, the number of large ascocarps produced by P. tritici-repentis was significantly reduced by Laetisaria arvalis, Ster ile II, and Limonomyces roseipellis under 24- and 48-h wetting periods but not under 6- and 12-h wetting periods compared to the uninoculate d control. Compared to field straw, suppression of ascocarp formation in axenic straw by the test fungi was much less. L. arvalis reduced as cocarp formation in the 24- and 12-h wetting treatments compared to th e uninoculated control. Under the 48-h wetting treatment, Sterile II i nhibited ascocarp formation in one experiment but increased ascocarp f ormation in the other. Limonomyces roseipellis did not inhibit ascocar p formation in axenic straw. Thus, ascocarp suppression in wheat straw by selected antagonistic fungi occurred only under relatively long (> 12 h) wetting periods.