Evol Ecol Res 12: 761-768 (2010)     Full PDF if your library subscribes.

Heritability under benign and stressful conditions in the plant pathogenic fungus Mycosphaerella graminicola

Yvonne Willi1,2, Rainer Follador1, Nina Keller1, Yves Schwander1 and Bruce A. McDonald1

1Institute of Integrative Biology, Plant Pathology, ETH Zürich, Zürich and 2Institute of Biology, Evolutionary Botany, University of Neuchâtel, Neuchâtel, Switzerland

Correspondence: Y. Willi, Institute of Biology, University of Neuchâtel, Rue Emile-Argand 11, CH-2009 Neuchâtel, Switzerland.
e-mail: yvonne.willi@unine.ch


Hypothesis: Stressful environmental conditions directionally change the heritability of quantitative traits and the short-term adaptive potential of populations.

Organism: Mycosphaerella graminicola, a haploid pathogenic fungus causing Septoria leaf blotch in wheat.

Methods: Isolates from a population of M. graminicola in Switzerland were used to estimate quantitative genetic variance components and broad-sense heritability of in vitro mycelial colony size under six environmental conditions.

Results: Environments varied in their effect on colony size, reflecting different levels of stress for the pathogen. Three standardized variance components – genotypic, environmental, and phenotypic – increased under stress. The increase in standardized genotypic variance under stress pointed towards increased relative evolvability of the colony size. In contrast, broad-sense heritability did not vary with stress, indicating no change in absolute evolvability of the trait.

Conclusions: Environmental stress is predicted to affect heritability, but empirical research has not produced convincing generalities. One reason may be that the focus has been on heritability instead of variance components. If both genetic and environmental variances change under stress, heritability can go up or down. We found that stress positively impacted standardized genetic variance, an alternative measure of relative evolvability.

Keywords: adaptability, benign vs. stressful, environment-dependence, environmental change, evolutionary potential, favourable vs. unfavourable, genetic variance, heritability.

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