ENHANCED PRODUCTION OF PYRENOPHORA-TRITICI-REPENTIS CONIDIAL SUSPENSIONS

A technique that yields conidial suspensions of Pyrenophora tritici-re pentis nearly free of other propagules involves growing the fungus in potato-dextrose broth, followed by removal, comminution, and inoculati on into liquid clarified V8 juice agar (CV8). After 48 hr of growth in the dark, the fungus is exposed to alternating periods of light and d ark that stimulate the production of conidiophores and conidia in a la wn covering the entire surface of the colony. In two tests using 24 is olates of P. tritici-repentis, inoculum suspensions were obtained with an average of 1,386 and 1,692 propagules (conidia, conidiophores, and hyphal fragments) per milliliter, in which 92 and 100%, respectively, of the propagules were conidia. In a third test, the use of a directe d stream of water to remove inoculum resulted in a suspension in which 98% of the total propagules were conidia. Use of a glass microscope s lide or a rubber spatula to scrape inoculum from agar surfaces resulte d in suspensions in which only 67% of the total propagules were conidi a. A fourth test demonstrated that conidial lawns resulted in inoculum yields two to three times greater than those obtained from conidial r ings formed on the periphery of fungal colonies grown on CV8 medium. T he technique enhances conidial yield and facilitates the production of conidial suspensions nearly free of other P. tritici-repentis propagu les. The technique will promote more precise and repeatable genetic an d epidemiological studies of tan spot of wheat.