Enhancing the efficacy of biocides with biochar to control Sclerotinia sclerotiorum, the cause of white mold in Calendula officinalis
摘要
Diseased samples of Calendula officinalis were collected from three governorates in Egypt, showing typical symptoms of white mold caused by Sclerotinia sclerotiorum. Compatibility assessments were conducted, classifying three compatible pure isolates based on all possible reactions. In the pathogenicity trial, pathogenic isolates demonstrated aggressive behavior towards Calendula with a disease infection of 100% and varying degrees of disease severity compared to the untreated control. The most aggressive isolate that produced the highest oxalic acid was identified. Its identity was confirmed through molecular methods. In vitro, the maximum suppressive effect of S. sclerotiorum on radial growth by was observed with the biocides Bio-Zeid® and Plant Guard®, which were enhanced by non-activated biochar, achieving reductions of 76.89 and 71.11%, respectively. All treatments combining biocides with biochar completely prevented the formation of sclerotia, compared to the untreated control. Greenhouse conditions demonstrated that all treatments significantly reduced disease incidence and severity, improved growth parameters, and increased chlorophyll and carotenoid production to varying degrees. The non-activated biochar treatment (1% w/w + Bio-Zeid® at 2.5 g/L) recorded the highest results, with plants reaching an average height of 85.33 cm, producing the greatest number of branches (21), and the highest number of inflorescences (38). In contrast, the untreated control exhibited average measurements of 20.33 cm in height, 5 branches, and 3 inflorescences. Additionally, the treated plants consistently showed the highest values for chlorophyll a (3.589), chlorophyll b (1.616), total chlorophyll (5.205), and carotenoids (1.979), compared to the untreated control values of 0.024, 0.015, 0.039, and 0.048, respectively.