Relationship between Leaf Wetness Period, Temperature and Infection of Venturia nashicola to Japanese Pear Leaves.

Abstract

The relationship between leaf wetness period, temperature and infection to Japanese pear leaves by artificial inoculation with conidia of Japanese pear scab fungus, Venturia nashicola, was investigated. The inoculated leaves developed symptoms slightly with 9-hr leaf wetting at 15°C, moderately with 12-hr leaf wetting at 5 and 25°C, and more heavily at 15 to 20°C. Leaves did not show, however, any symptoms at 30°C even with 36-hr leaf wetting, or less than 6-hr leaf wetting even at 5 to 25°C. These results are strikingly similar to those reported for apple scab by Mills. And these results coincide with the conidial and ascosporous germination status on water agar medium kept at 5 to 30°C, and behavior of conidial germination and penetration into leaf tissue with different wetting period kept at about 20°C. Based on the result that pathogenicity of ascospore is almost the same as conidial one, these results seem to be applied to the infection by ascospores.