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A biometrical study of the effect of nonspecific pathogenicity genes on host and pathogen fitness related characters in the Ustilago hordei-Hordeum vulgare system

University of British Columbia

Nine Ustilago hordei sporidia that produced 20 dikaryons were isolated at random from an F2 teliospore (18D1+ x 20C1-) descended from race 7 and race 11. The 20 dikaryons were homozygous for a dominant gene conferring virulence on the barley variety Trebi and were suspected of segregating for nonspecific pathogenicity genes on this variety. Varieties Odessa (the universal suscept, with no known specific resistance genes) and Trebi were inoculated with each dikaryon and 58 host and pathogen fitness related variables were measured. Yield reduction occurred both in diseased and healthy plants as a result of the dikaryon treatments. A statistically significant negative correlation between host and pathogen reproductivity was found (r=-0.466, P=0.0481) on Trebi but not on Odessa. Statistically significant differences among dikaryons were found for some fitness related variables. The segregation of nonspecific pathogenicity genes with pleiotropic effects was believed to cause these differences. One of the genes was found to be tightly linked to the mating locus, coupled with the "-" mating allele. Analysis of variance revealed significant dominance and/or epistatic interaction effects on fitness related variables. The two varieties reacted differently to the dikaryons. Pathogen isolates exhibited specific adaptation to Trebi but not to Odessa. The presence of the nonspecific pathogenicity genes was readily measured statistically on Trebi, in the background of a matched specific resistance gene but not on Odessa. The traditional method of measuring disease damage level (percent smutted plants) was determined to be a reliable estimator of pathogen fitness on Trebi (R²=0.84) and pathogen reproductivity on both varieties (r=0.902, P=0.0001 on Trebi and r=0.815, P=0.0001 on Odessa). Due to weak correlation, prediction of host fitness should not be attempted using values calculated with either of the two traditional methods of measuring disease damage level (percent smutted plants and percent smutted heads). Stepwise regression of various combinations of variables indicated that Trebi, Odessa or smut dikaryon fitness can be accurately estimated with certain predictor variables. Spearman rank correlation tests suggested that "constant (concordant) ranking" of dikaryons for percent smutted plants and for pathogen fitness was evident on Odessa and on Trebi (r=0.871, P=0.0001 and r=0.713, P=0.0004, respectively).

Text

2010-08-07

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http://hdl.handle.net/2429/27187

Botany

University of British Columbia

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