In‐vitro antifungal activity of several biorational fungicides against Calonectria pseudonaviculata, the causal agent of Buxus hyrcana blight

Abstract

In recent years, the outbreak of box blight disease caused by Calonectria pseudonaviculata in Caspian Hyrcanian forests of Iran makes it necessary to find both efficient and environmentally friendly compounds as possible alternatives to currently available fungicides. Seven biorational compounds were tested for inhibitory activities against mycelial growth and conidial germination of C. pseudonaviculata Cy‐08 under in‐vitro conditions. Potassium sorbate and salicylic acid as organic compounds and copper (II) sulphate and zinc sulphate as inorganic compounds completely inhibited both mycelial growth and conidial germination of Cy‐08 at 25 mM, comparable with the commercial fungicide, tebuconazole. Ammonium phosphate and boric acid were moderately inhibitory at 25 and 50 mM, also showing fungistatic effects at 100 mM. Ammonium sulphate had the weakest antifungal activity at all tested concentrations. The tested compounds altered the pH of the growing medium (with readings ranging from pH 4.2 to 7.85) but there was no correlation between pH of the amended media and inhibition of fungal growth. C. pseudonaviculata grew in both acidic and alkaline conditions, with mycelial growth decreasing at both lower (4‐5) and higher (11‐12) pH values. The antifungal activity of all tested chemicals was pH‐independent. Therefore, it can be concluded that the more active of these compounds may be used as part of an integrated management program for the control of boxwood blight in forest settings.

Humic and fulvic acids against boxwood blight disease caused byCalonectria pseudonaviculata

“…It could be suggested that the growth rate of this fungal isolate was affected by the acidity of the media, and these humic substances do not have antifungal properties. However, Yoldashkhan et al () studies showed that the growth of C. pseudonaviculata was pH‐independent, and this fungus could grow under both acidic and alkaline conditions (pH of 4–12). Therefore, it can be reasoned that effects of differing pHs on growth of C. pseudonaviculata were very minimal and that such humic substances do possess antifungal properties against the causal agent of boxwood blight disease.…”

“…The radial growth of Cy‐08 mycelia was measured 30 days post‐inoculation when the negative control colony completely enriched the plate area. Inhibition percentage was assessed by the following formula (Yoldashkhan, Samavat, & Zamanizadeh, ):…”

“…The pH of the PDA medium was not standardized across the treatments to limit the effect an altered pH would have on the potential antifungal activities caused by the aliphatic functional groups, and OH and COOH groups attached to the humic compounds (El‐Ghamry, Abd El‐Hai, & Ghoneem, ; Hahlbrock & Scheel, ). In addition, Yoldashkhan et al () showed that the growth of C. pseudonaviculata was pH‐independent, by demonstrating that this fungus could grow under both acidic and alkaline conditions (pH 4–12).…”