153 Breeding of Black Spot Resistance in Rose S. Yamaguchi 1, 2 and K. Boontiang 1, 3 1 Laboratory of Ornamental Plant Breeding, Faculty of Agriculture, Ehime University, Tarumi, Matsuyama, Ehime Pref., Japan 2 Present address: Lab. Ornamental Plant Breeding and Ethnobotany, Coll. Agr., Tamagawa Univ., Machida, Tokyo, Japan 3 Present address: Lab. Horticulture, Fac. Agr., MahasaraKhan University, Mahasarakhan, Kantarawichai, Thailand Keywords: rose breeding, disease resistance, black spot resistance, photosynthesis breakdown, convenient selection Abstract We report the dynamic change of photosynthesis rate of rose leaf after artificial inoculation of black spot disease. This experiment was scheduled for making up mores quick selection protocol for the high resistance against black spot disease during breeding program of rose. Photosynthesis in rose cultivars of ‘Tineke’ and ‘Asami Red (syn. = Rote rose)’ was daily measured after artificial infection of black spot. Significant breakdown of photosynthetic activity was appeared in four to seven days after inoculation in ‘Tineke’, however, the epidemic change in the symptom appeared after fourteen days. This physiological disorder, which appeared ahead for the visual observation for the epidemic appearance of symptom, will be useful tool for quick selection of black spot disease resistance breeding in rose. INTRODUCTION Leaves are the main factory for the photosynthesis and transpiration in plants. Due to these purpose, flat lamina has provided a large surface for absorbing sunlight, with stomata allowing the gases to pass in, and out of the leaf. In addition, an extensive network of veins brings water into the leaves and transports the glucose produced via photosynthesis activity to the rest of the plant body. The reaction of photosynthetic ratio on the exquisite leaves is almost attributed by several studies (Fraser and Bidwell, 1974; Davis et al., 1977, 1978; Connie et al., 1982). Necrotic leaf by black spot (Diplocarpon rosae Wolf.) is recognized at most serious among fungus disease of destructive effects in rose plants, due to the breakdown of photosynthesis caused by chlorophyll deficiency. This report consists of two main objectives: The rate of photosynthesis changing after the artificial inoculation and occurrence of disease symptom observation after inoculation. MATERIALS AND METHODS Isolation of Black Spot Two popular commercial varieties of rose, ‘Tineke’ and ‘Asami Red’, for cut flower production in Japan were selected and planted on rockwool cube in glass house and grew by nutrient water culture system in the green house. We also selected most virulent black spot isolate (Isolate ID, BSE:ROT) from our previous studies for the establishment of race isolates obtained from 20 varieties of garden rose (Boontiang et al., 2002). Inoculation Procedure Inoculation spore density was adjusted to 10 7 spores ml -1 in distilled water using a haemactometer. In this study, atomizer inoculation method (Scavejda and Bolton, 1980; Reddy et al., 1992; Walker et al., 1995) was applied onto the both sides of abaxial and adaxial surfaces of plant materials. After atomization, the artificially moistened condition Proc. V th IS on Rose Research and Cultivation Ed.: Y. Ueda Acta Hort. 870, ISHS 2010