MOLECULAR CHARACTERIZATION OF BLACK FOOT DISEASE PATHOGENS IN GRAPEVINE NURSERIES AND EVALUATION OF SOME FUNGICIDES FOR CONTROL OF THE MOST VIRULENT ISOLATES

Abstract

Black foot disease, which is mainly caused by Ilyonectria Chaverri & Salgado and Dactylonectria L. Lombard & Crous species, causes serious destruction in most of the wine and grape producing regions of the world, particularly in nurseries and young vineyards. The aim of this research was to evaluate the present situation of black foot disease in grapevine nurseries (Vitis Vinifera L.), to identify its potential agents at morphological and molecular levels and to develop a control strategy against isolates found as the major virulent ones in pathogenicity tests. This study also represents the first attempt to control black foot disease in grapevine saplings in Turkey. Preliminary surveys were carried out in 21 grapevine nurseries in the Aegean Region during 2019 growing season. Black foot species obtained from vine saplings were identified as Ilyonectria liriodendri (Halleen, Rego & Crous), Dactylonectria macrodidyma (Halleen, Schroers & Crous) and D. torresensis (A. Cabral, Rego & Crous), using morphological and molecular methods. The pathogenicity studies revealed that the most virulent isolates belonged to I. liriodendri. Twelve chemical and one biological fungicides were screened in vitro for mycelial inhibition of I. liriodendri isolates. The experiments were performed in three replicates for each of the chemical fungicides. Sterile distilled water, instead of fungicide solution, was used for control trials. Mixtures of cyprodinil + fludioxonil, thiabendazole + fludioxonil + metalaxyl–m + azoxystrobin and azoxystrobin + metalaxyl-m + fludioxonil were the most effective chemical fungicides tested in mycelial inhibition of I. liriodendri isolates. Chemical fungicides mixtures of boscalid + kresoxim-methyl, promocarb hydrochloride (HCL) + fosetyl-al, azoxystrobin + difenoconazole, fludioxonil + metalaxyl–m and individual fungicides; cyprodinil, fluoxapyroxad, hymexazole, fenhexamid and 8-hydroxyquinoline sulphate were not effective on mycelial inhibition. Biocontrol activity of Trichoderma harzianum Rifai KRL-AG2 strain against I. liriodendri was evaluated. The experiment was performed in four replicates for each isolate. Petri dishes with only I. liriodendri mycelial discs used as controls. Treatment with Trichoderma harzianum Rifai KRL-AG2 strain provided 60.1% to 80.6% inhibition against I. liriodendri isolates. The most effective fungicides tested in vitro were evaluated in 2020 and 2021 under controlled conditions against possible infections of I. liriodendri during the rooting process of 1103 Paulsen grapevine rootstocks. Mixtures of thiabendazol + fludioxonil + metalaxyl–m + azoxystrobin and cyprodinil + fludioxonil were the most effective fungicides in the experiments conducted in 2020 and 2021, followed by azoxystrobin + metalaxyl-m + fludioxonil and Trichoderma harzianum Rifai KRL-AG2 strain.