Abstract
Botrytis cinerea is a necrotrophic plant pathogenic fungus with a wide host range. Its natural populations are phenotypically and genetically very diverse. A survey of B. cinerea isolates causing gray mold in the vineyards of Castilla y León, Spain, was carried out and as a result eight non-pathogenic natural variants were identified. Phenotypically these isolates belong to two groups. The first group consists of seven isolates displaying a characteristic mycelial morphotype, which do not sporulate and is unable to produce sclerotia. The second group includes one isolate, which sporulates profusely and does not produce sclerotia. All of them are unresponsive to light. Crosses between a representative mycelial non-pathogenic isolate and a highly aggressive field isolate revealed that the phenotypic differences regarding pathogenicity, sporulation and production of sclerotia cosegregated in the progeny and are determined by a single genetic locus. By applying a bulked segregant analysis strategy based on the comparison of the two parental genomes the locus was mapped to a 110 kb region in chromosome 4. Subcloning and transformation experiments revealed that the polymorphism is an SNP affecting gene Bcin04g03490 in the reference genome of B. cinerea. Genetic complementation analysis and sequencing of the Bcin04g03490 alleles demonstrated that the mutations in the mycelial isolates are allelic and informed about the nature of the alterations causing the phenotypes observed. Integration of the allele of the pathogenic isolate into the non-pathogenic isolate fully restored the ability to infect, to sporulate and to produce sclerotia. Therefore, it is concluded that a major effect gene controlling differentiation and developmental processes as well as pathogenicity has been identified in B. cinerea. It encodes a protein with a GAL4-like Zn(II)2Cys6 binuclear cluster DNA binding domain and an acetyltransferase domain, suggesting a role in regulation of gene expression through a mechanism involving acetylation of specific substrates.
Highlights
Botrytis cinerea is an endemic phytopathogenic fungus with a necrotrophic lifestyle (van Kan, 2006) and a very wide host range (Elad et al, 2016)
Among the non-pathogenic isolates identified in this analysis two groups can be distinguished: a first class consists of seven isolates of the mycelial morphotype, which do not sporulate, do not produce sclerotia and neither infect V. vinifera nor P. vulgaris leaves, and a second class represented by a single isolate, B116, which sporulates, does not produce sclerotia, is unable to infect V. vinifera leaves but, being less aggressive than the B448 isolate, does infect P. vulgaris leaves
It is interesting to note that tracing the origin of the non-aggressive isolates indicated that they were purified from symptomatic bunches from which other aggressive B. cinerea isolates were purified
Summary
Botrytis cinerea is an endemic phytopathogenic fungus with a necrotrophic lifestyle (van Kan, 2006) and a very wide host range (Elad et al, 2016). It is the most important postharvest decay pathogen (Romanazzi and Feliziani, 2014) and the second most economically significant plant pathogen (Dean et al, 2012). In nature the fungus can reproduce both asexually and sexually It produces different cell and tissue types, including mycelium, micro- and macroconidia, sclerotia, apothecia and ascospores, which enable its reproduction and survival under different conditions. The arsenal of pathogenicity factors of the fungus, together with its versatility in reproduction and dispersal, make this pathogen difficult to control (Williamson et al, 2007)
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