Unveiling inoculum sources of black foot pathogens in a commercial grapevine nursery

Abstract

Black foot of grapevine is an important disease caused primarily by Ilyonectria spp. and “Cylindrocarpon” pauciseptatum. These pathogens affect grapevine nurseries and young vineyards, causing the decline and death of plants. In the nursery, the primary infections of the grafted cuttings are mainly attributed to soil-borne inoculum, which could infect the roots and the basal end of rootstocks during the rooting stage. The aim of this research was to detect other possible sources of inoculum throughout the different nursery stages by classical and molecular techniques (nested-PCR and multiplex nested-PCR). Results revealed the presence of the I. liriodendri and/or I. macrodidyma complex in grapevine rootstock and scion cuttings, cutting tools, water from hydration tanks, well water, callusing medium, one indoor air sample and soils collected from mother fields and nurseries. “Cylindrocarpon” pauciseptatum was only detected in the callusing medium, nursery soils, rooted-graftlings and on the root pruning machine. Forty four isolates obtained from soils (mother fields and nurseries) and rooted graftlings (six grapevine cultivar/rootstock combinations) were sequenced for part of histone H3 gene to resolve the species. While I. liriodendri, I. macrodidyma and I. torresensis were identified from soil samples, from rooted graftlings it was also possible to detect I. liriodendri, I. macrodidyma, I. novozelandica, I. torresensis, Ilyonectria sp. 2, “C.“ pauciseptatum and four Ilyonectria isolates which are close to I. cyclaminicola. The results demonstrated that, in addition to nursery soils, mother field soils, rootstock and scion cuttings, water from wells and hydration tanks, callusing media, cutting tools and indoor air should be considered as potential sources of inoculum for black foot pathogens.