Trichoderma as a potential biocontrol agent for Cercospora leaf spot of sugar beet

Abstract

Leaf spot disease caused by Cercospora beticola Sacc. (class Ascomycota, ord. Dothideales, fam. Mycosphaerellaceae) is the most destructive foliar disease of sugar beet. Commercial varieties are partially resistant and require repeated fungicide applications to obtain adequate protection levels; this has a high environmental impact and a risk of selecting resistant pathogen strains. A way of reducing chemical inputs could be to use biocontrol agents to replace or supplement fungicide treatments. A well-known class of biological control agents is represented by the fungi belonging to the Trichoderma genus (class Ascomycota, ord. Hypocreales, fam. Hypocreaceae), but there is a lack of information about its behaviour towards C. beticola. This study reports the evaluation of several Trichoderma isolates as possible biocontrol agents of this pathogen. Preliminary in vitro and in vivo assays led to the selection of two Trichoderma isolates characterised by their ability to reduce pathogen sporulation and antagonism towards the pathogen or competence for sugar beet phyllosphere. Repeated foliar applications of the liquid culture homogenate preceded by a single treatment of difenoconazole in 2 year trials under natural inoculum in field reduced the disease incidence and pathogen sporulation from the necrotic spots. An increase in sugar yield was also obtained by means of isolate Ba12/86-based treatments, perhaps due to induced resistance effects.