Abstract
When the influence of host species, inoculum density, temperature, leaf wetness duration, and leaf position on the incidence of gentian brown leaf spot caused by Mycochaetophora gentianae, was examined, the fungus severely infected all seven Gentiana triflora cultivars, but failed to infect two cultivars of G. scabra and an interspecific hybrid cultivar. Inoculum density correlated closely with disease incidence, and a minimum of 102 conidia/mL was enough to cause infection. In an analysis of variance, temperature and leaf wetness duration had a significant effect upon disease incidence, which increased with higher temperature (15–25°C) and longer duration of leaf wetness (36–72 h). No disease developed at temperatures lower than 10°C or when leaf wetness lasted <24 h. At 48-h leaf wetness, disease incidence was 0, 28, 77, and 85% at 10, 15, 20, and 25°C, respectively. Middle and lower leaves on the plant were more susceptible than upper leaves. In microscopic observations of inoculated leaves, >50% of conidia germinated at temperatures >15°C after 24-h leaf wetness. More appressoria formed at higher temperatures (15–25°C) with extended duration of leaf wetness (24–72 h). At 48-h leaf wetness, appressorium formation was 0, 8, 26, and 73% at 10, 15, 20, and 25°C, respectively. These results suggest that temperature and leaf wetness duration were important factors for infection of gentian leaves.
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Acknowledgments
The authors gratefully acknowledge Takashi Hikage (Hachimantai City Floricultural Research and Development Center) for sampling original gentian cultivars in Hachimantai City, Dr. Hiromitsu Furuya and Dr. Hidekazu Takahashi (Faculty of Biological Resources, Akita Prefectural University) for advice on the design of experimental and statistical methods, and Dr. Naoyuki Matsumoto (National Agricultural Research Center for Hokkaido Region) for critically reading the manuscript. This study was supported by “Research and development projects for application in promoting new policy of Agriculture Forestry and Fisheries” (No. 2040) from the Ministry of Agriculture, Forestry and Fisheries of Japan.
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Nekoduka, S., Tanaka, K. & Sano, T. Pathogenicity of Mycochaetophora gentianae, causal fungus of gentian brown leaf spot, as affected by host species, inoculum density, temperature, leaf wetness duration, and leaf position. J Gen Plant Pathol 76, 370–376 (2010). https://doi.org/10.1007/s10327-010-0274-x
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DOI: https://doi.org/10.1007/s10327-010-0274-x