Cell wall-degrading enzymes and parasitism of sclerotia are key factors on field biocontrol of white mold by Trichoderma spp.

Field outcomes of 10 Trichoderma spp. isolates against white mold (Sclerotinia sclerotiorum) on common beans were matched to laboratory results, to identify the causes of variance related to biocontrol effectiveness. Laboratory assays estimated sclerotia parasitism and production of the cell wall-degrading enzymes (CWDEs) lipase, NAGase, beta-1,3-glucanase, beta-glucosidase and protease. Field trials were carried out in 2009 and 2010 under a randomized block design and sprinkling irrigation, where 2 x 10(12) spores mL(-1) of each antagonist were applied to the plots at the early R5 stage. The density of S. sclerotiorum apothecia m(-2) and disease severity were assessed, respectively at R7 and R8 stages, with yield and its components also estimated for each year. Field results were analyzed jointly by the Tukey-Kramer multiple comparison test, and all variables from both field and laboratory experiments were subjected to principal component analysis (PCA). In both years, isolates TR696 and TR356 of Trichoderma asperellum were effective in reducing apothecia density and disease severity. Biocontrol increased the number of pods per plant and yields up to 40% when compared to controls, even under higher disease pressure in 2010. PCA demonstrated in 2009 and 2010 that apothecia density, disease severity, NAGase, beta-1,3-glucanase and number of pods were the main sources of the first component of variance. Such results suggest that the CWDEs NAGase and beta-1,3-glucanase and sclerotia parasitism are key components of Trichoderma spp. action in biocontrol of S. sclerotiorum in the field, and may be used as markers to hasten the selection of new, promising isolates. (C) 2013 Elsevier Inc. All rights reserved.