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Ecology and Epidemiology

Growth Dynamics of Xanthomonas campestris pv. oryzae in Leaves of Rice Differential Cultivars. P. A. Barton-Willis, Department of Plant Pathology, Throckmorton Hall, Kansas State University, Manhattan 66506, Present address: 107 Washington Crossing Road, Pennington, NJ 08534; P. D. Roberts(2), A. Guo(3), and J. E. Leach(4). (2)(3)(4)Department of Plant Pathology, Throckmorton Hall, Kansas State University, Manhattan 66506, (2)Present address: Department of Plant Pathology, University of Hawaii, Honolulu 96822. Phytopathology 79:573-578. Accepted for publication 28 November 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-573.

Bacterial multiplication and spread were monitored in race-specific interactions of Xanthomonas campestris pv. oryzae and rice (Oryza sativa). Bacterial numbers in compatible and incompatible interactions increased equally until levels reached 107108 colony-forming units/leaf. Thereafter, the bacterial growth rates in incompatible interactions slowed in comparison with those in compatible interactions. Maximum bacterial numbers per leaf were dependent on host cultivar. In both compatible and incompatible interactions, bacteria spread from the inoculation point; however, bacteria in compatible interactions spread more rapidly. Symptoms were not observed in advance of bacteria. Lesion lengths, in general, were positively correlated with bacterial numbers. When leaves were inoculated with bacterial mixtures (1:1 of race 1 or 6 [compatible] to race 2 [incompatible]), the growth rate of race 2 isolates was severely restricted compared with that of the control (race 2 alone). The same effects were observed in a host in which all races were compatible. The apparent interaction between bacterial isolates confounded analysis of the effect of mixed inoculations on race-specific resistance induction.