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Dark Therapy of Bean Rust. C. E. Yarwood, Professor, Department of Plant Pathology, University of California, Berkeley 94720; Phytopathology 62:1139-1140. Accepted for publication 12 April 1972. DOI: 10.1094/Phyto-62-1139.

When beans lightly infected with rust (less than 20 pustules/cm2 of the uredinal stage of Uromyces phaseoli [Pers] Winter on Phaseolus vulgaris L. 'Pinto') were held in the dark for 5 days or more, the rusted and nonrusted tissues were usually killed; but when held 3 days or less in darkness, neither tissue was severely injured. When beans, of which portions of the leaves had ca. 100 pustules/cm2, were placed in darkness for 2 to 4 days at 3 to 10 days after inoculation and then removed to the greenhouse, most of the rusted tissue became water-soaked and died, whereas the nonrusted tissue did not. If the fungus in the rusted tissue was killed with heat (5-50 sec at 50 C) before the dark treatment, the rusted tissue responded almost like the nonrusted tissue.