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Techniques

Selective Recovery of Xanthomonas spp. from Rice Seed. Di Ming, Department of Plant, Soil and Insect Sciences, University of Wyoming, Laramie 82071, Present address: Department of Plant Pathology University of Alaska, Fairbanks 9975-0080; Huazhi Ye(2), N. W. Schaad(3), and D. A. Roth(4). (2)(4)Department of Plant, Soil and Insect Sciences, University of Wyoming, Laramie 82071, (2)Present address: Department of Agronomy, Sichuan Agricultural University, Sichuan, China; (3)Harris-Moran Seed Co., San Juan Batista, CA. Phytopathology 81:1358-1363. Accepted for publication 17 July 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-1358.

A semiselective medium, called XOS, was developed to isolate Xanthomonas oryzae pv. oryzae and X. o. oryzicola from rice seed. The medium contains sucrose, peptone, monosodium glutamate, calcium nitrate, potassium phosphate, iron EDTA, cycloheximide, cephalexin, kasugamycin, methyl violet 2B, and agar. Recovery of X. o. oryzae, X. o. oryzicola and nonpathogenic Xanthomonas-like bacteria on XOS basal medium ranged from 98 to 162% (mean 121%) of the recovery on nutrient glucose agar after incubation at 28 C for 4 days. Addition of the selective inhibitors decreased recovery of non-Xanthomonas saprophytes in rice seed extracts by over 53%, compared to XOS basal medium. Several saprophytic bacteria common to some Chinese seed lots were not significantly reduced; however, the growth of such bacteria was decreased enough to allow detection of the slower growing xanthomonads. Recovery of different pathogenic strains of the rice xanthomonads varied significantly on XOS. Detection of Xanthomonas spp. from seed was dependent on partial maceration of seed and incubation of the resulting extract at 5 C for 2 h. Extracts from rice seed collected from asymptomatic plants in California and China and from plants with symptoms of bacterial leaf blight in China were plated on XOS, and colonies suggestive of Xanthomonas were isolated. Various identification assays indicate that these strains belong to the genus Xanthomonas; however, the strains were nonpathogenic when inoculated on a susceptible rice cultivar. XOS is quantitatively and qualitatively superior to other available media for isolation of Xanthomonas spp. from rice seed.