Pathogenicity of <Emphasis Type="Italic">Mycochaetophora gentianae</Emphasis>, causal fungus of gentian brown leaf spot,as affected by host species,inoculum density,temperature, leaf wetness duration,and leaf position |
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Authors: | Syuuichi Nekoduka Kazuaki Tanaka Teruo Sano |
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Institution: | (1) Iwate Agricultural Research Center, 20-1 Narita, Kitakami Iwate, 024-0003, Japan;(2) The United Graduate School of Agricultural Sciences, Iwate University, 18-8, Ueda 3 chome, Morioka 020-8550, Japan;(3) Faculty of Agriculture and Life Science, Hirosaki University, 3 Bunkyo-cho, Hirosaki Aomori, 036-8561, Japan |
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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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