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The Relation of Blocked Chloroplast Differentiation to Sugarcane Leaf Scald Disease. Robert G. Birch, Graduate student, Department of Plant Pathology, University of Hawaii, Honolulu 96822; Suresh S. Patil, professor, Department of Plant Pathology, University of Hawaii, Honolulu 96822. Phytopathology 73:1368-1374. Accepted for publication 5 April 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-1368.

Study of the ultrastructure of chlorotic leaf tissue from sugarcane and sweet corn with systemic leaf scald confirmed that the pathogen. Xanthomonas albilineans, was confined to the xylem during early disease development. Xylem vessels were sometimes blocked by tightly packed bacteria, but adjacent bundle sheath and mesophyll parenchyma were not invaded. Chloroplasts were absent from cells surrounding invaded vessels in narrow white leaf stripes, and from uninvaded white leaves emerging after invasion of sugarcane stalks by the pathogen. Proplastids, etioplasts, and vesicular forms, but no degenerating chloroplasts, were present in white leaf areas. The evidence suggests that X. albilineans in invaded xylem may produce a diffusible phytotoxin, which blocks chloroplast differentiation at the proplastid or etioplast stages.

Additional keywords: electron microscopy, Saccharum officinarum, Zea mays var. saccharata.