Effect of Primula root and other plant extracts on infection structure formation of Phyllosticta ampelicida (asexual stage of Guignardia bidwellii) and on black rot disease of grapevine in the greenhouse

The paper describes in vitro and in vivo experiments with extracts from Primula root and Hedera helix aimed at characterizing their effect on Phyllosticta ampelicida (teleomorph: Guignardia bidwellii), the causal agent of black rot disease of grapevine. In pre-tests, collodion membranes placed over water agar were determined to be better suited for spore germination and appressoria formation than cellophane sheets. On collodion membranes placed over water agar amended with different agents, the fungicide Polyram® WG (metiram) inhibited germination of the conidia of P. a m -pelicida completely. Inhibition by the extract from Primula root was similarly high and stronger than by the extract from H. helix. Primula root extract also inhibited conidial germination on grape leaves. In greenhouse tests, protective application of the extracts of H. helix and Primula root at concentrations of 1.0 and 0.5% reliably provided control of black rot with efficacy > 90%, which was in the same range as protection provided by the saponin-containing reference extracts from Sapindus mukorossi, Chenopodium quinoa and Quillaja spec.. In further tests, protective and curative activity (i.e. application of treatments 24 h before or 24 h after pathogen inoculation) was compared. The agents tested were extracts from Primula root and H. helix, Polyram® WG, the resistance inducer BION® 50 WG (acibenzolar-S-methyl) and Frutogard®, a product containing an extract from brown algae and phosphonate. When applied protectively, all treatments reduced the disease severity. The efficacy of primula root extract was similar to that of Polyram® WG, which provided complete control. Curative application caused a much lower reduction in disease, which was most pronounced for the Frutogard® treatment.