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Physiology and Biochemistry

Use of Race- and Cultivar-Specific Elicitors from Intercellular Fluids for Characterizing Races of Cladosporium fulvum and Resistant Tomato Cultivars. Verna J. Higgins, Department of Botany, University of Toronto, Toronto, Ontario, Canada, M5S 1A1; Pierre J. G. M. deWit, Laboratory of Phytopathology, Agricultural University, Binnenhaven 9, Wageningen, Netherlands. Phytopathology 75:695-699. Accepted for publication 18 December 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-695.

Intercellular fluids obtained by an in vacuo infiltration technique were used to compare and to characterize European and North American races of Cladosporium fulvum. In previous studies, it was found that such fluids contained specific elicitors of chlorosis and/or necrosis. The races of North American origin tested included race 0 with cycloheximide tolerance (C+), a race 4(C+) mutant derived from the race 0 (C+) isolate, race 2.3 (C+), race 4 with benlate tolerance (B+), and two isolates of race 2.3.4 (#3 and #78). Races 4, 5, and originating from the Netherlands were also tested. Intercellular fluids obtained from all compatible race-cultivar combinations showed race- and cultivar-specific elicitor activity when injected into tomato cultivars with genes conferring high phenotypic resistance (Cf2, Cf4, Cf5, and Cf9) and also when tested in a cultivar with gene Cf3 which allegedly confers only partial resistance. A cultivar with the gene Cf1, also giving partial resistance, behaved in a manner similar to cultivars with no known genes for resistance, i.e., none of the elicitor preparations induced chlorosis or necrosis. Fluids obtained from races with the same virulence spectrum but originating from different continents or by artificial means showed identical race and cultivar specificity. Fluids obtained by using the complex race, which is virulent on all European commercial tomato cultivars but not on two recently released Ontario hybrids, showed activity only in the hybrids. Polyacrylamide gel electrophoresis of intercellular fluids confirmed that preparations with necrosis activity on cultivar Sonatine contained a fast-moving basic peptide. The mannose/glucose ratios of fluids obtained from previously designated compatible and incompatible interactions had ranges of 1.45 to 3.10, and 0.50 to 0.71, respectively. In interactions in which partial resistance due to genes Cf1 or Cf3 was originally expected, the ratios ranged from 0.52 to 3.92, but for each interaction the ratio corresponded to the estimated degree of colonization based on elicitor activity and histological examination.

Additional keywords: Fulvia fulva, gene-for-gene interaction, leaf mold of tomato, Lycopersicon esculentum.