Abstract
Many cryptic species have recently been discovered in fungi, especially in fungal plant pathogens. Cryptic fungal species co-occurring in sympatry may occupy slightly different ecological niches, for example infecting the same crop plant but specialized on different organs or having different phenologies. Identifying cryptic species in fungal pathogens of crops and determining their ecological specialization are therefore crucial for disease management. Here, we addressed this question in the ascomycete Botrytis cinerea, the agent of gray mold on a wide range of plants. On grape, B. cinerea causes severe damage but is also responsible for noble rot used for processing sweet wines. We used microsatellite genotyping and clustering methods to elucidate whether isolates sampled on gray mold versus noble rot symptoms in three French regions belong to genetically differentiated populations. The inferred population structure matched geography rather than the type of symptom. Noble rot symptoms therefore do not seem to be caused by a specific B. cinerea population but instead seem to depend essentially on microclimatic conditions, which has applied consequences for the production of sweet wines.
Highlights
Since the advent of molecular biology, the use of genetic markers within the population genetics framework has revealed the existence of many cryptic species, that is, species previously unrecognized based on morphology alone, in a wide range of organisms (e.g., Taylor et al 2000; Gentetaki and Lynn 2010; Heimeier et al 2010; Jesse et al 2010; Kreier et al 2010; Nygren et al 2010; Gladieux et al 2011a,b; Liu et al 2011; Piggott et al 2011)
The aims of this study are (i) to determine whether noble rot symptoms are caused by B. cinerea or by a cryptic distinct species, (ii) in case noble rot symptoms are caused by B. cinerea sensu stricto, to investigate whether genetic differentiation exists between populations of B. cinerea causing respectively gray mold and noble rot symptoms, and (iii) to investigate genetic differentiation between populations from different French vineyards used for sweet wine production
Both in the full data set and in the region 9 symptom subsamples, most multilocus genotypes (MLGs) obtained with the eight microsatellites were each detected in a single individual, resulting in a G/N ratio of 0.93 in total and never lower than 0.94 within subsamples (G: number of different MLG, N: sample size)
Summary
Since the advent of molecular biology, the use of genetic markers within the population genetics framework has revealed the existence of many cryptic species, that is, species previously unrecognized based on morphology alone, in a wide range of organisms (e.g., Taylor et al 2000; Gentetaki and Lynn 2010; Heimeier et al 2010; Jesse et al 2010; Kreier et al 2010; Nygren et al 2010; Gladieux et al 2011a,b; Liu et al 2011; Piggott et al 2011) This is especially true for microorganisms like fungi, because few morphological traits can be used to discriminate species and because inducing mating in vitro to test for interfertility is often impossible or less discriminant than other species criteria (Koufopanou et al 1997; Dettman et al 2003a,b; Fournier et al 2003; Le Gac et al 2007a,b; Giraud et al 2008). Beyond the fundamental interest in understanding the coexistence of sibling species in ecology, it is essential for disease management to recognize the different cryptic species in fungal pathogens of crops and their ecological specialization, as they can exhibit differences in fungicide resistance (Fournier et al 2005), phenologies (Walker et al 2011), organ specialization (Fitt et al 2006), host specialization (Le Gac et al 2007a; Fournier and Giraud 2008), or ability to infect resistant plant varieties
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