ENHANCED PRODUCTION OF PYRENOPHORA-TRITICI-REPENTIS CONIDIAL SUSPENSIONS

A technique that yields conidial suspensions of Pyrenophora tritici-repentis nearly free of other propagules involves growing the fungus in potato-dextrose broth, followed by removal, comminution, and inoculation 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 dark that stimulate the production of conidiophores and conidia in a lawn covering the entire surface of the colony. In two tests using 24 isolates 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 directed stream of water to remove inoculum resulted in a suspension in which 98% of the total propagules were conidia. Use of a glass microscope slide or a rubber spatula to scrape inoculum from agar surfaces resulted in suspensions in which only 67% of the total propagules were conidia. A fourth test demonstrated that conidial lawns resulted in inoculum yields two to three times greater than those obtained from conidial rings formed on the periphery of fungal colonies grown on CV8 medium. The technique enhances conidial yield and facilitates the production of conidial suspensions nearly free of other P. tritici-repentis propagules. The technique will promote more precise and repeatable genetic and epidemiological studies of tan spot of wheat.