3.4.15
RESISTANCE TO MUME SCAB CAUSED BY THE FUNGUS VENTURIA CARPOPHILA (ANAMORPH CLADOSPORIUM CARPOPHILUM)

Y ADACHI, T HAJI, H YAEGAKI, H IEKI and M YAMAGUCHI

National Institute of Fruit Tree Science, MAFF, Tsukuba, Ibaraki 305-8605, Japan

Background and objectives
The mume (Prunus mume) originated in south-eastern China, and has been cultivated in Japan since ancient times. The fruit was too acid for table fruit, therefore was processed as pickles or in liquor. Scab, caused by Venturia carpophila Fisher, is one of the most important diseases of stone fruits including mume in Japan. The market value of the fruit is reduced by the appearance of small, oval, olive-to-black spots and cracking by the coalescence of lesions. Although control of scab is presently dependent on spraying with fungicides, planting of resistant cultivars is considered to be one of the most effective means. Scab resistance, however, has been little researched in Prunus sp. The objective of the present work is evaluations of scab resistance in numerous mume cultivars.

Materials and methods
Scab resistance in 48 mume cultivars was evaluated in the Chiyoda experimental orchard, National Institute of Fruit Tree Science, where mume trees had been severely infected under natural conditions. During mid-June to mid-July in 1996 and 1997, 100 fruits were randomly collected from two trees of each cultivar. Disease severity was assessed by scoring the number and degree of diseased fruits.

Results and conclusions
There were great differences in scab resistance among mume cultivars. The percentage of diseased fruits ranged from 0.0 to 98.0 in 1996, and from 14.7 to 100.0 in 1997. The disease severity was between 0.0 and 77.3 in 1996, and between 3.6 and 94.8 in 1997. Both data were closely related in each year. Although there was no cultivar which is immune, mume cultivars could be classified from highly susceptible to resistant groups. This result suggested that scab resistance is quantitative. Cultivars of Bungo (Kurume), Tamabotan, and Sarasa were highly susceptible. More than 85% of the fruits were severely infected with scab fungus in 1996 and 1997. On the other hand, no lesion was observed on more than 70% of the fruits of Tounoume, Inazumi and Taiwan ume 85485 cultivars. These cultivars appear to be useful as genetic sources of resistance in breeding. But it is necessary to confirm the resistance by inoculation testing. However, inoculation tests are little reported [1], because this pathogen has poor sporulation in culture. We have established a method for spore preparation of V. carpophila, and succeeded in the reproduction of scab on fruits by inoculation with spores formed on medium. In 1998, therefore, our next work will be to reconfirm the surveys of resistance in the orchard by inoculation testing.

References
1. Bensaude M, Keitt GW, 1928. Phytopathology 18: 313-329.