New insights in Ilyonectria black foot disease of grapevine.

Considering the growing importance of black foot disease of grapevine, this study was aimed to deeply understand details on taxonomy, genetics, biology and pathological behaviour of its main causal agents, previously attributed mostly to Ilyonectria liriodendri and I. macrodidyma. A multi-gene analysis of a collection of Ilyonectria isolates, along with morphological characterisation, enabled the description of 12 species from I. radicicola and four from I. macrodidyma complexes. Among these, pathogenicity experiments revealed I. lusitanica, I. estremocensis and I. europaea as more virulent to grapevine than I. liriodendri and I. macrodidyma. The entire mating-type loci of I. liriodendri and of species from the I. macrodidyma complex were obtained. While the idiomorph structure of species from the latter matches that of other heterothallic Hypocreales, the organization of the mating-type loci in I. liriodendri seems unique, suggesting a potential pseudo-heterothallism. Soilborne inoculum is accepted to contribute significantly to initiate black foot disease in grapevine plants. qPCR amplification from DNA soil samples demonstrate that rotation can reduce the levels of Ilyonectria in nurseries, and that levels of infestation in vineyard soils are lower than in nursery or mother-plant soils. Additionally, a protoplast transformation protocol is presented for the stable integration of the GFP gene in the genome of I. liriondendri, enabling future downstream functional genetic studies