Efficacy of Hypochlorite in Disinfesting Nonfungal Plant Pathogens in Agricultural and Horticultural Plant Production: A Meta-Analysis

Biocontrol Agents of Fusarium Head Blight in Wheat: A Meta-Analytic Approach to Elucidate Their Strengths and Weaknesses

The use of biocontrol agents (BCAs) coping with fungal pathogens causing Fusarium head blight (FHB) is a compelling strategy for disease management, but a better elucidation of their effectiveness is crucial. Meta-analysis is the analysis of the results of multiple studies, which is typically performed to synthesize evidence from many possible sources in a formal probabilistic manner. This meta-analytic study, including 30 pathometric, biometric, physiochemical, genetic, and mycotoxin response variables reported in 56 studies, evidences the BCA effects on FHB in wheat. The effectiveness of BCAs of FHB in wheat in terms of pathogen abundance and disease reductions, biomass and yield conservation, and mycotoxin prevention/control was confirmed. BCAs showed higher efficacy (i) in studies published more recently; (ii) under controlled conditions; (iii) in high susceptible wheat cultivars; (iv) when Fusarium inoculation and BCA treatment did not occur directly on the plant (i.e., at the seed and kernel levels) in terms of disease development and mycotoxin control, and vice versa in terms of biomass conservation; (v) if Fusarium inoculation and BCA treatment occurred by spraying spikes in terms of yield; (vi) at 15 to 21 days post Fusarium inoculation or BCA treatment; and (vii) if they were filamentous fungi. However, BCAs overall were less efficacious than conventional agrochemicals, especially in terms of pathogen abundance and FHB reductions, as well as of mycotoxin prevention/control, although inconsistencies were reported among the investigated moderator variables. This study also highlights the complexity of reaching a good balance among BCA effects, and the need for further research.

A Systematic Review and Quantitative Synthesis of the Efficacy of Quaternary Ammonium Compounds in Disinfesting Nonfungal Plant Pathogens

This quantitative review and systematic analysis of the effectiveness of quaternary ammonium compounds (QACs) in disinfesting nonfungal plant pathogens in agricultural and horticultural cropping systems is a complementary follow-up to a previous study that evaluated the efficacy of QACs against fungal plant pathogens. In the present study, a meta-analysis involving 67 studies was conducted to assess the overall efficacy of QACs against plant pathogenic bacteria, oomycetes, and viruses and to identify factors associated with observed differences in product efficacy. Across all studies, QACs resulted in a significant (P < 0.0001) reduction in either disease intensity or propagule viability with a mean Hedges' g ([Formula: see text]) of 1.75, indicating that overall QAC treatments were moderately effective against nonfungal pathogens. Significant differences in product efficacy were observed between organism types (P = 0.0001), with QAC interventions resulting in higher efficacy (P = 0.0002) against oomycetes ([Formula: see text] = 4.20) than against viruses ([Formula: see text] = 1.42) and bacteria ([Formula: see text] = 1.07), which were not different (P = 0.2689) from each other. As a result, bacterium and virus types were combined into a composite set (BacVir). QAC intervention against BacVir resulted in significant differences in efficacy within categorical moderator subgroups for genus (P = 0.0133), target material (P = 0.0001), and QAC product generation (P = 0.0281). QAC intervention against oomycetes resulted in significant differences in efficacy only for genus (P < 0.0001). For the BacVir composite, five random effect (RE) meta-regression models were significant (P = 0.05), where models with dose and time, dose and genus, time and genus, dose and target, and time and target accounted for 62, 61, 52, 83, and 88%, respectively, of the variance in true effect sizes (R2) associated with [Formula: see text]. For oomycetes, three RE meta-regression models were significant (P = 0.05), where models with dose and time, dose and genus, and time and genus accounted for 64, 86, and 90%, respectively, of R2 associated with [Formula: see text]. These results show that while QACs are moderately effective against nonfungal plant pathogens, the observed variability in their efficacy due to dose of active ingredient and contact time of these products can be influenced by organism type, genus within organism type, the target being treated, and the generation of QAC products.

A Systematic Review and Quantitative Synthesis of the Efficacy of Quaternary Ammonium Disinfestants Against Fungal Plant Pathogens

Quaternary ammonium compounds (QACs) have been used as disinfestants in plant production systems since the late 20th century. In studies on the control of fungal pathogens in agricultural and horticultural crop production systems, the efficacy of QAC disinfestants is variable, ranging from very high to ineffective. A systematic review and meta-analysis were performed to establish and understand how pathogen- and application-related factors influenced product efficacy. The meta-analysis was based on 124 studies involving 14 fungal plant pathogen genera, eight target materials, and four generations of QAC products that contained different mixtures of active ingredients. A significant (P < 0.0001) reduction in either disease intensity or propagule viability resulted following disinfestation using QAC products. Hedges' g standardized mean difference (g̅₊) across the studies was 2.16, indicating that QACs, on average, were highly effective against fungal pathogens. Heterogeneity was significant (P < 0.0001), indicating that effect sizes (g) were not representative of a common mean effect size and supported selection of a random effects model. In all, 78.5% of the observed variance consisted of variance in true effects with a high estimate of between-study variability (τ² = 2.15). For fungal genus, subgroup g̅₊ for genera Pseudonectria and Calonectria was significantly (P < 0.0038) higher than for all other genus subgroups, except Fusarium. For target materials, subgroup g̅₊ for solution, cloth, plant, and metal were significantly (P > 0.0071) higher than for inorganic material or wood. For product generation, subgroup g̅₊ for fifth-generation products was significantly (P > 0.0071) higher than for fourth-, third-, and second-generation products. Dose and time accounted for only 8 and 4%, respectively, of the true variance in effect sizes in the regression model dose, time, and dose-time (P = 0.0004). Genus accounted for 40 and 51% of the true variance in effect sizes in the regression models dose and genus (P = 0.0008) and time and genus (P = 0.0007), respectively. Target material accounted for 18 and 19% of the true variance in effect sizes in the regression models dose and target (P = 0.0001) and time and target (P = 0.0001), respectively. QAC product generation accounted for 24 and 21% of the true variance in effect sizes in the regression models dose and QAC generation (P = 0.0034) and time and QAC generation (P = 0.0189), respectively. These results show that the current recommended rates for dose and contact time are generally expected to result in effective disinfestation for commercial QAC products. However, the efficacy against fungal plant pathogens is likely to be influenced by the fungal genus and target being treated and the generation of the QAC product that is used for disinfestation.

Fusarium spp. Associated with Dendrobium officinale Dieback Disease in China

A rare plant species of the Orchidaceae family, Dendrobium officinale is considered among the top ten Chinese medicinal herbs for its polysaccharide. Since 2021, when the dieback disease of D. officinale was first reported in Yueqing City, Zhejiang Province, China, Fusarium isolates (number = 152) were obtained from 70 plants in commercial greenhouses. The disease incidence ranged from 40% to 60% in the surveyed areas. Multilocus sequence analysis (MLSA) coupled with morphological characterization revealed that the collected isolates belonged to five species (sp.), viz., Fusarium concentricum, F. fujikuroi, F. nirenbergiae, F. curvatum, and F. stilboides, with isolation frequencies of 34.6%, 22.3%, 18.4%, 13.8%, and 10.5%, respectively. Notably, at least two Fusarium species were simultaneously isolated and identified from the infected plants. Finally, the pathogenicity test results demonstrated that such species were responsible for the dieback disease of D. officinale. However, F. concentricum and F. fujikuroi were more invasive compared to the other species in this study. To the best of the authors’ knowledge, this study was the first report of F. concentricum, F. curvatum, F. fujikuroi, F. nirenbergiae, and F. stilboides causing the dieback disease of D. officinale in China and worldwide. This work provides valuable data about the diversity and pathogenicity of Fusarium populations, which will help in formulating effective strategies and policies for better control of the dieback disease.