Flooding freshly harvested oospores in sterile distilled water (SDW) for several days enhanced germination in 3 out of 4 isolates of Phythium oligandrum. Treatment of SDW‐flooded oospores with myo‐inositol increased germinability during the first 20 days of storage at 15°C. Seed dressing with oospores of P. oligandrum controlled pre‐ and post‐emergence damping‐off of sugar‐beet caused by soil‐borne P. ultimum and seed‐borne Phoma betae. For some isolates, flooded oospores in SDW and treatment with myo‐inositol increased efficacy of the seed dressing. However, no significant control of damping‐off caused by Rhizoctonia solani was observed.
On corn‐meal agar, P. oligandrum coiled around and penetrated hyphae of P. ultimum and R. solani, but did not interfere with Ph. betae.
Seed treatment with ascospores of Chaetomium globosum reduced damping-off of sugar-beet caused by seed-borne Phoma betae and soil-borne Pythium ultimum or Rhizoctonia solani in growth chamber experiments. Seed treatment with a fluorescent Pseudomonas sp. controlled Ph. betae and P. ultimum but not R. solani. Coating cotton seeds with ascospores controlled P. ultimum and R. solani damping-off. In some experiments, biological seed treatments were equally or more effective than seed treatment with captan. However, greater variability in disease control occurred with the antagonists than with captan. Fifty percent of freshly harvested ascospores of C. globosum germinated in 8 h on water agar. When ascospores were stored under air-dried conditions for 3 days to 2.5 years, germination increased to > 90%. Under same storage conditions, survival of Pseudomonas sp. was detected after 4 months. Antagonistic activities observed in vitro were hyphal coiling of C. globosum on R. solani, and mycostasis was induced by C. globosum or Pseudomonas sp. on agar and soil. The presumed cause of mycostasis is the diffusible antifungal metabolites which may also be involved in the biological control of damping-off.
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 hypae 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 cropin 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.
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