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Scanning Electron Microscopy of Virulent and Avirulent Strains of Xanthomonas campestris pv. oryzae on Rice Leaves. T. W. Mew, International Rice Research Institute (IRRI), Los Baņos, Laguna, Philippines; I-pin C. Mew(2), and J. S. Huang(3). (2)International Rice Research Institute (IRRI), Los Baņos, Laguna, Philippines; (3)North Carolina State University, Raleigh 27650. Phytopathology 74:635-641. Accepted for publication 31 January 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-635.

Multiplication of strains of Xanthomonas campestris pv. oryzae on rice (Oryza sativa) cultivars and penetration of the bacteria through water pores of leaf blades were investigated with scanning electron microscopy. No marked difference in numbers of cells was noted on the leaf surface 1 hr after spray-inoculation on all cultivar-strain combinations. Twenty-four hours after inoculation, bacteria of strain PX061, which is virulent to cultivars TN1 and CAS 209, multiplied immediately outside the water pores and some bacteria had gained entrance through these pores. Cells of PX0101, a strain that has lost its virulence, did not multiply significantly on the leaf surface and appeared to be embedded in a thin layer of exudate secreted by the water pores. The exudate eventually sealed the opening of these pores. Bacterial cells of PX086, which is virulent to TN1 but avirulent to CAS 209, multiplied on the water pores of TN1 but were trapped in the exudate of CAS 209 48 hr after inoculation. Bacterial cells of all three strains were not observed to multiply on stomata of either cultivar. These results suggest that bacteria are immobilized and inhibited from dividing by excretions from water pores in incompatible host-bacteria combinations. Site specificity of bacterial multiplication on leaf surface was also observed.

Additional keywords: epiphytes, resistance.