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Physiology and Biochemistry

Cross-Protection with Strains of Potato Spindle Tuber Viroid in the Potato Plant and Other Solanaceous Hosts. R. P. Singh, Research scientist, Agriculture Canada, Research Station, P.O. Box 20280, Fredericton, New Brunswick, Canada, E3B 4Z7; A. Boucher, and T. H. Somerville. Virology technicians, Agriculture Canada, Research Station, P.O. Box 20280, Fredericton, New Brunswick, Canada, E3B 4Z7. Phytopathology 80:246-250. Accepted for publication 5 September 1989. Copyright 1990 Department of Agriculture. Government of Canada. DOI: 10.1094/Phyto-80-246.

When nucleic acids containing a mild and a severe strain of potato spindle tuber viroid (PSTV) were coinoculated to several potato cultivars, 1937% of inoculated plants became infected with both strains. Variation of nucleic acids concentration favored dominance of one or other strain. However, both strains replicated in second generation plants grown from tubers from doubly inoculated plants. With potato cultivars of different resistances, cross-protection between strains of PSTV was determined by the absence of the challenge strain, which was detected by return-polyacrylamide gel electrophoresis. Cross-protection was complete in the highly susceptible Russet Burbank, but incomplete in tolerant BelRus. Second-generation potato plants infected with a single strain and grown from greenhouse or field-infected tubers were completely protected against reinoculation with another strain irrespective of the cultivar resistance, and no challenge strain was detected. However, protection was readily broken by changing the method of challenge inoculation. Studies of cross-protection with eight experimental host plants indicated that protection was more complete in those hosts in which the protecting strain multiplied rapidly and spread to the entire plant rather than in those where PSTV infection was difficult or the spread of the viroid was erratic. These studies point out that the extent of cross-protection depends highly on the host plant.

Additional keywords: complete cross-protection, coinoculation, host-range, return-electrophoresis, replication of viroids, secondary infection, viroid strains.