Two races of Cladosporium fulvum new to Ontario and further studies of Cf1 resistance in tomato cultivars

Abstract

Two races of Cladosporium fulvum, hitherto not encountered from the Niagara Peninsula or adjacent areas of Ontario, Canada, are reported as races 11 and 12. They are described in terms of their infection capabilities on differential tomato hosts carrying the Cf1, Cf2, Cf3, or Cf4 resistance genes. A tabular summary compares the infection capabilities of races 11 and 12 with those of four other presently available C. fulvum races on the differential hosts used for their characterization. Of the four resistance genes which have been incorporated in the various tomato cultivars only Cf1 and Cf4 appear to condition resistance to race 11 and only Cf1 to race 12. Results of inoculation studies with C. fulvum under controlled conditions of light, temperature, and relative humidity are discussed. Comparative studies of their reaction to races 1 and 12 indicate that certain tomato cultivars reported to carry the Stirling Castle, or Cf1, resistance no longer possess it and that additional resistance genes may be present in others.