The Relationship ofXanthomonas campestrispv.translucensto Frost and the Effect of Frost on Black Chaff Development in Wheat

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Abstract
The relationship of Xanthomonas campestris pv. translucens to frost injury and subsequent colonization and infection of wheat [Triticum aestivum] plants was investigated. Ice nucleation activity (INA) of nine strains of X. c. pv. translucens was determined according to the droplet test at -9 C. Frost damage and lesion development on plants were tested at -4 and -3 C. All nine strains of X. c. pv. translucens were INA-positive. Wheat, barley, bean, and corn plants sprayed to runoff with suspensions containing 108 colony-forming unit s(cfu) of X. c. pv. translucens per milliliter sustained greater frost damage than plants inoculated with water alone. The amount of frost damage to plants increased significantly when the time of exposure to frost or the time between inoculation and cold treatment increased. Lesions developed more rapidly in plants subjected to frost than in plants not exposed to frost. Lesions also increased in size and number as the incubation time increased between inoculation and freezing. Frost damage and disease severity in plants were directly related to the number of INA bacteria present on those plants during the frost period. As few as 30 cfu of X. c. pv. trnslucens per square centimeter of leaf area resulted in increased frost injury. X. c. pv. translucens is capable of epiphytic growth on wheat plants, and frost damage may be enhanced by epiphytic populations of this bacterium, which can, in turn, increase disease severity.