A LEAF INOCULATION METHOD FOR DETECTION OF XANTHOMONAS-ORYZAE PV. ORYZICOLA FROM RICE SEED

A leaf-inoculation method for detecting Xanrhomonas oryzae pv. oryzico la in rice seed was developed and tested. The method is based on inocu lating leaf segments on agar with seed washings in a moist chamber. Fr eshness of inoculated leaf segments is maintained by addition of 75 to 100 ppm benzimidazole to the 1% water agar after sterilization. Using cells from pure cultures, the minimum inoculum concentration to initi ate leaf streak lesions on the segments was found to be 10(3) CFU/ml. Inoculum prepared from seeds harvested from severely infected mother p lants induced lesions typical of leaf streak, followed by bacterial oo ze. With 4 g of seed, the incubation period was 3.5 days and bacterial ooze appeared within 5 days. The minimum amount of seed needed to det ect the bacterium based on seed washings varied according to disease s everity of the mother plants. The bacteria isolated from lesions on th e leaf segments were confirmed as X. oryzae pv. oryzicola after bacter iological, serological, and Biolog tests were conducted. The results c onfirm that the detached-leaf method is as simple and reliable as the immuno-radiometric assay and inoculation on intact pot-grown rice plan ts in the greenhouse.