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Induction of Pisatin Formation in the Pea Foot Region by Pathogenic and Nonpathogenic Clones of Fusarium solani. John A. Christenson, Postdoctoral Research Associate, Department of Plant Pathology, Washington State University, Pullman, Washington, 99163, Present address of senior author: Department of Biology, Carroll College, Helena, Montana 59601; Lee A. Hadwiger, Associate Professor, Department of Plant Pathology, Washington State University, Pullman, Washington, 99163. Phytopathology 63:784-790. Accepted for publication 13 December 1972. DOI: 10.1094/Phyto-63-784.

The pisatin-inducing potential and the relative pisatin sensitivity of two pathogenic and two nonpathogenic clones of Fusarium solani were compared to evaluate the role of pisatin as a resistance component in the foot region of pea seedlings grown in infested soil. High quantities of pisatin accumulated more quickly in the foot region (basal stem, upper taproot and hypocotyl) of peas grown in nonsterile soil infested with clones of Fusarium solani f. sp. phaseoli than with clones of F. solani f. sp. pisi. However, after a slight delay, pathogenic clones were eventually responsible for the highest accumulation of pisatin/gram of tissue. The pattern of pisatin accumulation described above was partially obscured when F. solani clones were added to soil with a higher percent organic matter, since such soil promoted substantial increases in the pisatin in seedlings in the absence of the F. solani inoculum. Percentage spore germination, rate of germ-tube growth, linear growth on agar and sporulation of all F. solani clones were retarded when grown in vitro at pisatin concentrations of 30 to 200 µg/ml and the pathogenic clones did not consistently excel as the most pisatin insensitive. However, pathogenic clones did consistently excel in degrading pisatin. The pisatin sensitivity of both pathogenic and nonpathogenic clones was associated with the potential of pisatin to inhibit protein synthesis in the fungus. On the basis of dramatic increases in protein synthesis observed only in pea tissue inoculated with a nonpathogenic clone of F. solani, we suggest that pisatin production in pea seedlings may be coupled with additional host responses which cumulatively render the plant resistant.

Additional keywords: pea root rot, phytoalexin.