VIEW ARTICLE

Etiology

Pseudomonas aeruginosa: Cause of Internal Brown Rot of Onion. E. J. Cother, Plant Pathologist, Agricultural Research Centre, Yanco, N.S.W., 2703, Australia; B. Darbyshire(2), and J. Brewer(3). (2)(3)Senior Research Scientist and Technical Officer respectively, C.S.I.R.O. Division of Irrigation Research, Griffith, N.S.W., 2680, Australia. Phytopathology 66:828-834. Accepted for publication 20 January 1976. DOI: 10.1094/Phyto-66-828.

From the results of biochemical tests and its utilization of 108 carbon sources, a pathogenic bacterium isolated from diseased onions was identified as Pseudomonas aeruginosa. In inoculation studies, lesions were formed only in the leaf bases near the center of the bulb. No lesions formed in immature bulbs, and no infection developed in wound-inoculated leaves. The pattern of disease development suggested that infection occurred at harvest, but in vitro experiments failed to support this. Glucose, fructose, and sucrose were the only soluble sugars in the leaf base tissue. Soluble sugars comprised up to 77% of the dry weight of the outer leaf bases; but only about 8% of the dry weight of the inner leaf bases. The importance of soluble sugars in disease development was examined and a potential mechanism of bulb infection is discussed.