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Erwinia-Induced Internal Necrosis of Immature Cotton Bolls. L. J. Ashworth, Jr., Plant Pathologist, Crops Research Division, ARS, USDA, U.S. Cotton Research Station, Shafter, California 93263; D. C. Hildebrand(2), and M. N. Schroth(3). (2)(3)Plant Pathologists, respectively, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 60:602-607. Accepted for publication 16 October 1969. DOI: 10.1094/Phyto-60-602.

Internal necrosis of immature cotton bolls was observed in the San Joaquin Valley of California in 1965. The necrotic tissue was reddish brown in color, and affected locules had a soft, slimy consistency. Affected seed coats also were discolored, and the seed contents often were completely decayed. Lint of infected mature open bolls was tan in color, and the locules were compact instead of having the white and fluffy consistency of healthy mature bolls. A bacterium, probably a strain of Erwinia herbicola, was associated with the disease. It induced typical symptoms of the disease when flowers and bolls were inoculated. In absence of insect transmission, locular necrosis appeared to depend on occurrence of super-numerary carpels. Development of this secondary internal boll splits the placentae and results in an opening to the outside of the bolls and in intertwining of the fibers of affected locules. This allows the bacterium to enter the boll, where it spreads from the interplacentae space into locules.