Understanding pitfalls and proposing strategies to optimize the biological control of white mold (Sclerotinia sclerotiorum)

Abstract

We evaluated during seven crop seasons; 74 uniform field trials conducted throughout Brazil to assess the performance of biological control products on the reduction of the carpogenic Sclerotinia sclerotiorum sclerotium germination. The mean difference (MD) by three products classes (Trichoderma, Bacillus and Mixed) was summarized (59 trials, k = 340). Separate network meta-analysis to determine the influence of three classes (low, moderate, and high) of average monthly temperature (AMT) and average monthly rainfall (AMR) on biocontrol performance. All three product classes significantly reduced carpogenic germination, with fitted 𝑀𝐷̅̅̅̅̅ values of -10.6270 for Bacillus, -8.5928 for Trichoderma, and -7.0177 for Mixed. For (AMT) and (AMR), only interactions of genus and low or moderate AMT and AMR were statistically significant from zero (p < 0.1), indicating that high AMT and AMR affected biocontrol of carpogenic germination. The second manuscript, we evaluated carpogenic germination, colonization and crop yield, on soybean and succeeding crops (Wheat and Maize). Here, we found sclerotia germination rates from 31.0% to 61.6%, (P = 0.583) in soybean crop. Colonization by BCAs from 4.7% to 19.4% (P = 0.174). Also, biological and chemical application disease incidence (P = 0.520), range from 73.7% to 87.2% and yield production from 2001 to 2803kg/ha. For succeeding crops, carpogenic germination interaction (crop x treatments) effect was observed (P=0.328). However, the treatments reduced carpogenic germination (P=0.011), control was 65.7% and treatments until 47.0%. For Crop factor (p=0.022), maize germination rate from 51.71% to 63.85% and wheat crop from 39.24% to 62,65%. Evaluated colonization, treatments (P=0.157), crop (p<0.001) and interaction (crop x treatment) (p=0.048). For colonization in Maize range from 2.23% to 10.15 %. For Wheat, treatments range from 16.6% to 39.8%. Wheat yield production (p=0.177) and Maize yield (p=0.593). The last part of our study, we investigated that effect of dressing-seed by Trichoderma sp. to biological agent can growth endophytically and promote tissue development on wheat plants. Additionality, viability of Trichoderma persists on tissues after Glyphosate applied and their ability to colonize sclerotia of Sclerotinia sclerotiorum. At the 7th day after planting shoot (P = 0.318) however root (P = 0.010) increased 28%, and at 20th day after planting, for aerial parts (P=0.049). Plants treats with Trichoderma sp. increased shoot length by 10,7%. Additionally, root length (P = 0.008) increased by 18,7%. T. asperellum levels detected on roots at 20 days after planting up to 1 x 10 4. Followed by roots at 7 days after planting up to 1 x 10 3. For shoots at 7 and 20 days, up to 1 x 10 2. After Glyphosate, the presence of T. asperellum decreased to 1 x 10 2 root, and to 1 x 10 1 in the bottom leaf. Carpogenic germination (P = 0.419) that control (31.2%) and Trichoderma (26.7 %). Thus, its stability and improved efficacy can be improved considering the dominant whether (rainfall and temperature) and cover crop (wheat). In turn, wheat may serve as a crop to selective buildup the population of the antagonist.