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Cotyledon and Leaf Ultrastructure of a Bacterial Blight-Immune Cotton Line Inoculated with a Low Level of Xanthomonas campestris pv. malvacearum. Ali H. Al-Mousawi, Graduate student, Department of Plant Pathology, Oklahoma State University, Stillwater 74078; P. E. Richardson(2), M. Essenberg(3), and W. M. Johnson(4). (2)Associate professor, Department of Botany, Oklahoma State University, Stillwater 74078; (3)Department of Biochemistry, Oklahoma State University, Stillwater 74078; (4)Joint appointment with the Langston University Cooperative Research Program, Langston University, Langston, OK 73050. Phytopathology 72:1230-1234. Accepted for publication 11 February 1982. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1230.

Cotyledons and foliage leaves of the cotton line Im 216, which is immune to bacterial blight, were inoculated with a low level inoculum (5 105 cells/ ml) of Xanthomonas campestris pv. malvacearum, and examined by light microscopy and transmission electron microscopy. Degenerative changes in some of the mesophyll cells were apparent 2 days after inoculation. Bacteria were found in samples taken 5 and 6 days after inoculation and were located in intercellular spaces near collapsed mesophyll cells. Fibrillar material was associated with all bacteria observed but did not completely envelop all the bacteria. Clusters of bacteria were larger than observed in an earlier ultrastructural study of Im 216 cotton cotyledons inoculated with a higher cell number but were similar to compact masses of bacteria observed previously in light microscopic studies of Im 216 cotyledons inoculated with 7 10 5 cells per milliliter of X. campestris pv. malvacearum.