Abstract
The author reported in this paper about the influences of air temperature to the incubation period of black spot disease of Japanese pear. The results are summarized as follows.
No difference was recognized on the percentage of spore germination in various temperature, 12, 16, 20 and 28°C in water drops on glass slide, but the length of germ tube after 16 hours was not similar, as 256μ, in 28°C and 108μ in 12°C.
Healthy pear leaves were inoculated with the spore suspension and then treated as follows:
1-3. Kept in wet chamber at 24°C, 16°C and 12°C, respectively.
4. Kept in wet chamber at 16°C after incubated at 24°C for 4 hours.
5. Kept in wet chamber at 12°C after incubated at 24°C for 4 hours.
When inoculated leaves were incubated at 24°C, the lesions appeared after 24 hours. On the other hand in 16° or 12°C, the lesions appeared after 2 or 3 days respectively.
The incubation period was not shortened when the inoculated leaves were incubated at 24°C for 4 hours, which were sufficient time for the fungus invading into the host tissue, before they were removed to 12 or 16°C.
From these experimental results, the following consideration may be done that the influence of air temperature to the incubation period of the disease is due to the reaction of mycelial growth of causal fungus in host tissue after invasion.
