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Title: Efficacy of hypochlorite as a disinfestant against fungal pathogens in agricultural and horticultural plant production: a systematic review and meta-analysis

item Copes, Warren
item OJIAMBO, PETER - North Carolina State University

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2020
Publication Date: 8/1/2021
Citation: Copes, W.E., Ojiambo, P.S. 2021. Efficacy of hypochlorite as a disinfestant against fungal pathogens in agricultural and horticultural plant production: a systematic review and meta-analysis. Phytopathology. 111:1369-1379.

Interpretive Summary: Chlorine compounds have a long history of usage as disinfestants to inactivate plant pathogens. Many studies have shown disinfestants to be highly effective, while others have shown moderate to poor activity against some plant pathogens and when treating some production surfaces. Commercial labels of chlorine (Cl) disinfestants do adjust rates and contact times depending on the application or surface area being treated, but the adjustments may not be comprehensive enough. A systematic literature review was done to obtain an overview of control responses and variances resulting from chlorine disinfestant applications to inactivate bacteria, fungi, oomycetes, viroids and viruses in multiple production applications. A meta-analysis was performed on data involving plant pathogen and disease control in production of agricultural and horticultural plant hosts, including four subgroup analyses on three Cl-disinfestant products, on sixteen dose and contact time combination categories, on four taxonomic organism categories, and on eight substrate categories. Significant differences were found with the more meaningful differences between substrates and taxonomic organisms. One problem was the high heterogeneity of effect size means. Discussion addresses how heterogeneity could be promoted by organism diversity, organism sensitivity to Cl-disinfestants, and Cl-disinfestant reactivity to substrates. The results address efficacy of disinfestant products that are commonly used in all agricultural and horticultural production systems.

Technical Abstract: Hypochlorite is often used as a disinfestant of fungal pathogens in agricultural and horticultural settings. However, reports of its effectiveness are variable across studies. A meta-analysis was conducted to assess the efficacy of hypochlorite against fungal pathogens and explore factors that explain the heterogeneity. Standardized mean effect size was calculated for each of the 109 studies. Random-effects meta-analyses were conducted on Hedges’ g to estimate the overall mean effect size g+ and determine the heterogeneity among studies. Hypochlorite resulted in a significant reduction in disease intensity or propagule viability indicating treatments were effective. However, 95% prediction intervals from -0.18 to 4.68 indicate hypochlorite could be ineffective against some populations. Random-effects analyses of categorical moderator values showed hypochlorite treatments were significantly more effective against disinfest spores in aqueous solution than on plastic, plant and wood. Similarly, hypochlorite was significantly more effective against Thielaviopsis spp. than Verticillium spp. Meta-regression indicated dose, contact time and their interaction on g+ were significant. Dose and time explained 0% and 16% of the variance in true effects, respectively. Continuous variable of dose or time, a categorical variable of target or genus and their interaction term explained 7% to 19% of the variance. These results show that although the current recommended dose and contact time for commercial bleach products are expected to result in effective disinfestation, the target material and genera of the fungal pathogen of interest will likely influence their efficacy.