Comparative in vitro antagonism of Trichoderma longibrachiatum, T. harzianum and T. asperellum against Sclerotinia sclerotiorum, the cause of stem and crown rot of alfalfa

Abstract Stem and crown rot caused by Sclerotinia sclerotiorum is a serious disease of alfalfa ( Medicago sativa L.), and effective antagonists are needed for its biological management. This study compared the in vitro antagonism of three Trichoderma isolates, T. longibrachiatum (FMB 0031), T. harzianum (FMB 0012) and T. asperellum (FMB 0032), against S. sclerotiorum (FMB 0090) in a dual-culture assay. Pathogen colony growth toward the antagonist was recorded after 3, 5 and 7 days in a completely randomised design with three replications, and percentage inhibition of radial growth (PIRG) was calculated relative to the untreated control. All three antagonists significantly reduced pathogen growth at every observation. Averaged over the three observations, pathogen growth was 0.48 cm with T. longibrachiatum , 0.56 cm with T. harzianum and 0.71 cm with T. asperellum , against 3.33 cm in the control. At 7 days, PIRG was 86.5, 85.1 and 78.7%, respectively. T. longibrachiatum and T. harzianum did not differ significantly, and both suppressed the pathogen more than T. asperellum at 7 days. Inhibition by T. asperellum rose from 73.0% at 3 days to 81.6% at 5 days, then declined, whereas inhibition by the other two isolates was maintained. T. longibrachiatum and T. harzianum are therefore the more promising candidates for formulation and further testing against stem and crown rot of alfalfa. Confirmation in pot and field studies, and study of the mechanisms involved, is still required.