Evaluations of the inhibitory activity of biofungicides, chemical inducers and plant extracts against conidial germination of Erysiphe heraclei DC, the causal organism of carrot powdery mildew

Powdery mildew of carrot, caused by Erysiphe heraclei DC, is one of the most important fungal diseases affecting the vegetative parts of the plant, causing severe damage to the resulting root crop. This study was designed to investigate the inhibitory activity of selected fungicide alternatives: biofungicides, chemical inducers, and plant extracts against E. heraclei conidial germination under in vitro conditions. The results showed that all biofungicides significantly inhibited conidial germination at all tested concentrations, especially at 2000 ppm compared to untreated spores. Bio-Mix (Bacillus subtilis + Trichoderma harzianum) was the most effective, followed by Bio-F (B. subtilis), while Trix-F (T. harzianum) was the least effective. The corresponding mean inhibition values were 74.1, 61.3, and 52.6%, respectively. Among the chemical inducers, salicylic acid at a concentration of 2000 ppm showed the highest inhibitory activity on spore germination (57.6%), followed by potassium silicate (44.8%), while citric acid showed the least activity (29.2%). As for plant extracts, the aqueous extract of germinated barley grains had the best effect (53.5%), followed by the germinated wheat grain extract (43.6%), lemongrass leaf extract (36.6%), and basil leaf extract (24.3%), while the germinated corn grain extract had the least effect (16.8%). The 40% concentration was more effective in inhibiting germination than the other concentrations. Complete inhibition of E. heraclei conidia germination was recorded using Micronite 80% at all tested rates, followed by Vinger 45% and Carbendazim 50%, recording 100, 88.9, and 85.5%, respectively.