PARAQUAT - A TOOL FOR THE QUICK DEVELOPMENT OF LATENT FUNGAL-INFECTIONS AND ENDOPHYTIC FUNGI

Detached winter wheat leaves without any symptom of fungal infection were thoroughly washed, surface desinfected, treated with paraquat (0.03-0.32% a.i.) and incubated on nutrient agar or in moist chambers under sterile conditions. Microscopic examinations showed that hyphae and yeast cells emerged from several stomata within 48-72 h after treatment. Fungal colonies developed on agar within the same period of time. More than 27 filamentous fungal genera and yeasts were identified during a wheat crop in healthy, green leaves. Non-treated leaves showed very few early emergences of fungi from stomata, but senescent leaves eventually yielded several fungal taxa observed after paraquat treatment. Similar observations were made on non-detached wheat leaves, and on detached sugarbeet leaves. Paraquat also induced development of Fusarium spp. from detached healthy winter wheat ears before or after heading. In grape berries, paraquat induced the development of latent infections of Botrytis cinerea a few days after treatment. The usefulness of paraquat for the detection of endophytes and for the diagnosis of early and latent fungal infections in plants, and the possible involvement of endophytes in tissue senescence are discussed.