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Growth of Homologous and Heterologous Phytopathogenic Bacteria in Cotton Lines Susceptible, Resistant, or Immune to Blight. Melanie B. Bayles, Department of Agronomy, Oklahoma State University, Stillwater 74078, Current address: 421 East 2825 North, Provo, UT 84604; William M. Johnson, Center for Small Farm Research, Southern University and A&M College, Baton Rouge, LA 70813 (formerly Agricultural Research Programs, Plant Protection Section, Langston University, Langston, OK 73050 and Department of Plant Pathology, Oklahoma State University, Stillwater 74078). Phytopathology 75:515-519. Accepted for publication 6 November 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-515.

In vivo growth studies of homologous (Xanthomonas campestris pv. malvacearum races 1, 3, 7, and 18) and heterologous (X. campestris pv. campestris, X. campestris pv. phaseoli, and Pseudomonas syringae pv. pisi) phytopathogenic bacterial populations were made to determine growth trends in blight-susceptible (line Ac 44), blight-resistant (lines Ac B2, Ac B3, Ac b7, OK 1.2, and OK 2.3), and blight-immune (line Im 216) cotton (Gossypium hirsutum). Relative population trends for homologous pathogen-cotton line combinations were similar, in general, to those found in other host-pathogen systems. Populations of heterologous pathogens in Ac 44 declined rapidly after reaching peak levels considerably lower than the peak levels of homologous pathogens. In contrast to results reported in previous studies, heterologous populations in the most resistant host, Im 216, were similar to homologous populations in the same line. This suggests that a nonspecific resistance mechanism operates in Im 216 which inhibits growth of all of these phytopathogenic bacteria. Population trends in cotton lines with intermediate levels of homozygous resistance resulted in final populations intermediate between those of Ac 44 and Im 216.

Additional keywords: bacterial blight of cotton, hypersensitive response.