VIEW ARTICLE

Physiology and Biochemistry

The Role of Pisatin Tolerance and Degradation in the Virulence of Nectria haematococca on Peas: A Genetic Analysis. K. J. Tegtmeier, Graduate research assistant, Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Present address of senior author: Department of Agricultural Biochemistry, University of Nebraska, Lincoln 68583; H. D. VanEtten, associate professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 72:608-612. Accepted for publication 6 April 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-608.

A series of crosses were made between isolates of Nectria haematococca mating population VI that differed in sensitivity to the pea (Pisum sativum) phytoalexin, pisatin. The progeny were tested for sensitivity to pisatin, ability to demethylate pisatin, and virulence on pea. The progeny from some crosses fell into two discrete classes of sensitivity. All progeny in the most tolerant class were able to demethylate pisatin; none in the more pisatin-sensitive class could demethylate this phytoalexin. Tetrad analysis of one of these crosses indicated that at least two loci conferred the tolerant, demethylating phenotype. The progeny from two other crosses did not segregate into distinct classes. In these crosses pisatin sensitivity segregated polygenically, and some of the most sensitive progeny were able to demethylate pisatin. In four crosses, virulence on pea segregated in the progeny. Of the 345 progeny analyzed, all of the moderately or highly virulent progeny were tolerant of pisatin and able to demethylate it. Therefore, either pisatin tolerance and demethylating ability are required for virulence on pea or genes for pisatin tolerance and demethylating ability are closely linked to genes for virulence. The results of this study indirectly support the hypothesis that pisatin accumulation is an active mechanism of resistance in pea.