Molecular polymorphism and phenotypic diversity in the generalist, wood-decay fungus Eutypa lata

Authors: TRAVADON, RENAUD - University Of California; Baumgartner, Kendra

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2014
Publication Date: 2/1/2015
Publication URL: http://apsjournals.apsnet.org/doi/pdf/10.1094/PHYTO-04-14-0117-R
Citation: Travadon, R., Baumgartner, K. 2015. Molecular polymorphism and phenotypic diversity in the generalist, wood-decay fungus Eutypa lata. Phytopathology. 105:255-164.

Interpretive Summary: The wood-canker fungus Eutypa lata infects a broad range of plant species and is, thus, considered to be a generalist pathogen. However, reports of species that suffer from Eutypa dieback (i.e., severe disease symptoms) are restricted to the cultivated hosts grapevine and certain species of stone fruits, namely apricot. In California, the pathogen reproduces not only on these cultivated crops, but also on native species (e.g., willow). In the present study, we evaluated the multi-host epidemiology of Eutypa dieback in California, based on a combination of population genetics analyses of pathogen populations from three hosts (grapevine, apricot, willow), and cross-inoculations involving the two most economically and historically-important hosts, grapevine and apricot. The cultivated hosts are likely more important than willow as inoculum reservoirs, as revealed by higher pathogen prevalence and allelic richness. Nonetheless, the absence of patterns of host specialization and local adaptation suggest frequent pathogen migration among all three hosts examined. Indeed, clustering analyses of haplotypes revealed no grouping based on host or location, suggesting no host differentiation in E. lata. We believe that our approach will facilitate advances in understanding the population biology and ecology of this and other tree pathogens. Specifically, we provide explanations for the generation and maintenance of a broad host range for this fungus, in particular in California, likely a recently geographic area colonized by this fungus.

Technical Abstract: Pathogen adaptation to different ecological niches can lead to host specialization and, when coupled with reproductive isolation, ecological speciation. We tested the hypothesis of host specialization in northern California populations of the fungus Eutypa lata, which causes a soft-rot wood decay in > 90 plants. Population genetic analyses of nine microsatellite loci in 182 isolates from three hosts (cultivated hosts grapevine and apricot, wild host willow) and three locations were complemented by cross-inoculation experiments on the cultivated hosts, to reveal patterns of either host specialization or local adaptation. The cultivated hosts are likely more efficient than willow at disease transmission, as revealed by higher pathogen prevalence and allelic richness. Nonetheless, high levels of gene flow were revealed among the three hosts and locations. Clustering analyses of haplotypes revealed no grouping based on host or location, suggesting no host differentiation in E. lata. Cross-inoculation experiments further supported this finding; there were no significant differences in either life-history trait (pathogenicity or aggressiveness) based on host or location. Random mating within E. lata populations and frequent immigration among populations may prevent fixation of alleles controlling host adaptation. The generation and maintenance of a broad host range in this pathogen, and in the relatively recent introduction area of California, suggests pre-adaptation of E. lata to utilization of diversified substrates/ resources. Pathogenicity traits acquired during past co-evolutionary interactions, resulting from close interaction with a particular host species, may allow the pathogen to infect novel hosts with similar defense mechanisms and/or similar xylem anatomy/ physiology.