First report of Dactylonectria alcacerensis, Dactylonectria macrodidyma and Ilyonectria liriodendri associated with black-foot disease of grapevine in Argentina

PLANT DISEASE

AMER PHYTOPATHOLOGICAL SOC

Año: 2022

0191-2917

Black-foot is a fungal disease that affects young vines and planting material in the countrieswhere grapevines are cultivated. During the 2018 grape-growing season, symptoms ofreduced vigor, short internodes, leaf chlorosis, root rot and necrosis in the base of plantswere observed in vines between 2 to 10 years old from 400 ha of vineyards of Mendoza andSalta regions. A total of 30% of the vineyards of cultivars Malbec, Cabernet Sauvignon andAspirant Bouchet, and rootstocks 101-14 Millardet et de Grasset and 1103 Paulsen, hadvines with disease symptoms. Vines had 15% disease incidence and 30% disease severity.These symptoms have been described as characteristic of black-foot, caused by?Cylindrocarpon?-like asexual morph fungi. Isolations were made from roots and basal partof 30 symptomatic plants. Fragments of advanced necrotic tissue were washed with runningwater, surface sterilized with 70% alcohol for 20 seconds, 2% NaOCl solution for 4 minutesand rinsed in sterile distilled water twice. These fragments were placed onto Potato DextroseAgar (PDA) and incubated at 25°C in the dark for 10 days to isolate fungal pathogens. Atotal of 50 colonies resembling black-foot disease pathogens were subcultured onto freshPDA in order to obtain single spore cultures. The isolates developed buff to cinnamon anddark brown, and felty mycelium. Colonies subcultured in synthetic nutrient agar (SNA)produced hyaline, cylindrical, straight and/or slightly curved with one to three septate (35.6× 5.3 µm) macroconidia and abundant, hyaline, ellipsoidal and zero to one septate (12.5 ×6.0 µm) microconidia. Cultures and conidia morphological characteristics were similar tothose of Ilyonectria or Dactylonectria genera (Cabral et al. 2012a; Lombard et al. 2014).DNA sequence analysis of the partial histone H3 gene was obtained for isolates INTA SC1(I. liriodendri), INTA LC2 (D. alcacerensis) and INTA LC1 (D. macrodidyma) and depositedin GenBank (accession nos. OK338901, OK338900 and OK338899). The BLAST searchwas conducted against type specimens. Sequences showed high similarity (99% to 100%)to the sequences of Ilyonectria liriodendri (Halleen, Rego & Crous) Chaverri & Salgado(GenBank accession no. JF735509), Dactylonectria alcacerensis (A. Cabral, Oliveira &Crous) L. Lombard & Crous (GenBank accession no. JF735630) and Dactylonectriamacrodidyma (Halleen, Schroers & Crous) L. Lombard & Crous (GenBank accession no.JF735647). Pathogenicity tests were conducted under greenhouse conditions on 1-year-oldrooted canes cv Malbec using the three isolates. Ten rooted cuttings with pruned roots wereimmersed in a suspension of 106 conidia ml-1 of each isolate for 60 min (Cabral et al. 2012b) while control cuttings were immersed in sterile distilled water. Immediately they were plantedin pots and kept in a greenhouse at a temperature between 25 to 30°C. Symptomsdeveloped on all plants 4 months after inoculation and consisted in necrotic lesions of rootsand in the base of the canes, with a reduction in root biomass. Plants did not develop aerialsymptoms. All fungi were re-isolated only from necrotic lesions of root and base of inoculatedcanes, fulfilling Koch´s postulates. No symptoms were observed on the control plants. Toour knowledge, this is the first report of the species I. liriodendri, D. alcacerensis and D.macrodidyma associated with black-foot disease of grapevine in Argentina. Black-footdisease has a negative effect on the viability of planting material and young vines, and thisreport will assist with monitoring distribution of the disease as well as developingmanagement recommendations to nurseries and grape growers in Argentina.