In vitro efficacy and storage stability of a talc-based Trichoderma longibrachiatum formulation against Sclerotinia sclerotiorum, the cause of stem and crown rot of alfalfa

Abstract Stem and crown rot caused by Sclerotinia sclerotiorum is a damaging disease of alfalfa ( Medicago sativa L.), and biocontrol formulations that stay viable in storage are needed to reduce reliance on fungicides. This study developed a talc-based formulation of Trichoderma longibrachiatum (isolate FMB 0031) and assessed its in vitro efficacy against S. sclerotiorum (isolate FMB 0090) and its storage stability. The formulation was prepared by mixing a millet-grown T. longibrachiatum powder with talc, potato powder and carboxymethyl cellulose (CMC). It was tested at 1/100, 1/1000 and 1/10,000 dilutions in a dipping assay, with colony growth recorded after 3, 5 and 7 days. Viability was determined monthly for six months of storage at room temperature by serial dilution plating. All dilutions reduced pathogen growth significantly relative to the untreated control. Mean colony growth was 0.61, 0.70 and 0.77 cm at 1/100, 1/1000 and 1/10,000, respectively, against 3.71 cm in the control, equivalent to 83.6, 81.1 and 79.2% inhibition. The 1/100 dilution was the most effective at every observation. The viable count was 3.4 × 10 8 cfu g − 1 at preparation and declined slowly over the first three months (87% of the initial count retained), then more quickly, reaching 1.5 × 10 8 cfu g − 1 (44% of the initial count) after six months. The talc-based formulation therefore combined strong in vitro suppression of S. sclerotiorum with substantial viability over six months of storage. Evaluation in pot and field trials is required before the formulation can be recommended for alfalfa production.