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.

Trichoderma and the Plant Heritable Priming Responses

“…However, it should not be forgotten that many Trichoderma strains live and can be isolated from the aboveground parts of the plant [ 29 ], where they endophytically colonize leaves and stems [ 30 ]. Some strains of Trichoderma are effective in the direct control of pathogens in the phyllosphere, although their mechanism of action seems to be linked more to induced resistance and mycoparasitism than to direct competition [ 31 ]. Selected Trichoderma strains may also release VOCs related to plant growth promotion [ 32 ] but may also be involved in reducing energy losses and inducing photosynthesis and resistance to foliar pathogens, such as those producing powdery mildew [ 33 ].…”

Biocontrol Mechanisms of Trichoderma koningiopsis PSU3-2 against Postharvest Anthracnose of Chili Pepper

“…Moreover, metabolites, such as volatile organic compounds (VOCs), secreted from the Trichoderma species have been applied to promote plant growth [ 8 , 9 , 14 ]. Application of the Trichoderma species has been used to reduce the disease severity of leaf spots on lettuce [ 12 ] and sugar beet [ 15 ], as well as brown spots on rice [ 16 ]. Biological control presents low human health risks, as well as an environmentally friendly method without the excessive use of chemical fungicides in various crops.…”

Inhibitory effects of antagonistic bacteria inhabiting the rhizosphere of the sugarbeet plants, on Cercospora beticola Sacc., the causal agent of Cercospora leaf spot disease on sugarbeet

“…Whereas these approaches are relatively effective in disease control, some of the approaches, such as resistant varieties, are not favoured by producers because of their lower agronomic properties (Weiland and Koch 2004;Galletti et al 2008). Resistance to CLS in commercial sugarbeet varieties is polygenic and quantitative (Smith and Gaskill 1970;Smith 1985;Skaracis and Biancardi 2000).…”