Genetic and virulence diversity, and mating type distribution of Togninia minima causing grapevine trunk diseases in Spain

Abstract

Fifty eight single-spore Togninia minima (anamorph Phaeoacremonium aleophilum) isolates were recovered from grape rootstock wood of plants that showed symptoms of Petri disease and esca from 2001 to 2008 in Spain. These isolates were studied by means of mating type distribution, UP-PCR analysis, and virulence assays. Analysis of clone-corrected data sets showed equal frequencies of both mating types in the entire Spanish population, in the Ciudad Real region, at inter-vineyard and intra-vine spatial scales; while unequal mating type distribution was detected in Valencia and Zaragoza regions, at intra-vineyard and intra-vine spatial scales. This is the first study on distribution of T. minima mating types on spatial scales varying from vineyards to regions. A total of 49 polymorphic UP-PCR markers were obtained using seven UP-PCR primers. Four optimal clusters were inferred with Bayesian structure and multivariate analyses from the UP-PCR data. The high number of unique genotypes observed within the Spanish population, combined with a near-equal distribution of mating types, suggested that sexual reproduction probably does occur. However, based on allele distribution and frequency, each of the three subpopulations appeared to be evolving independently. Gene and genotype diversities across the subpopulations were similar and ranged from 0.24 to 0.27 and from 0.27 to 0.37, respectively. The detection of genetically identical isolates within and among subpopulations indicates that an asexual reproductive component should not be excluded. Contrast analysis among groups defined by UP-PCR analyses showed no significant differences in the virulence of T. minima isolates.