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Infection Behavior of Venturia nashicola, the Cause of Scab on Asian Pears

First author: The Graduate School of Science and Technology, Kobe University, Hyogo 657-8501, Japan; second author: National Institute of Agro-Environmental Sciences, Tsukuba, Ibaraki 305-8604, Japan; third, fourth, and fifth authors: National Institute of Fruit Tree Science, Tsukuba, Ibaraki 305-8605, Japan; and sixth author: Chiba Experimental Agriculture Station, Chiba 266-000, Japan

The infection of Japanese pear by Venturia nashicola, the cause of scab on Asian pears (Japanese pear, Pyrus pylifolia var. culta; Chinese pear, P. ussuriensis), was examined using light and electron microscopy to determine the mechanism of resistance in pears. Early stages of infection were similar on the susceptible cv. Kosui, the resistant cv. Kinchaku, and the nonhost European pear (P. communis) cv. Flemish Beauty. V. nashicola penetrated only the cuticle layer on pear leaves and formed subcuticular hyphae on all three cultivars. Hyphae were localized in the pectin layer of pear leaves and never penetrated into the cytoplasm of epidermal cells. This restriction of fungal growth suggested that pectinases released by infection hyphae or subcuticular hyphae may be important in infection. Subcuticular hyphae were modified ultrastructurally in the pectin layer of resistant pear cultivars accompanied by fungal cell death. In contrast, fungal cells appeared intact in susceptible pear cultivars, suggesting the existence of resistance mechanisms.

Additional keywords: disease resistance, electron microscopy, pear scab, pectin.