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

Authors: Copes, Warren; OJIAMBO, PETER - North Carolina State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2021
Publication Date: 12/1/2021
Citation: Copes, W.E., Ojiambo, P.S. 2021. Efficacy of Hypochlorite in Disinfesting Nonfungal Plant Pathogens in Agricultural and Horticultural Plant Production: A Meta-Analysis. Plant Disease. 105:4084-4094. https://doi.org/10.1094/PDIS-09-20-2046-RE.
DOI: https://doi.org/10.1094/PDIS-09-20-2046-RE

Interpretive Summary: Bleach products have been used to kill plant pathogens for 80 years. Many studies have shown these disinfestants to be highly effective, while others have shown moderate to poor efficacy. A systematic literature review was done to obtain an overview of how well these disinfestants have controlled bacterial, oomycete, viroid and viral plant pathogens in agricultural and horticultural plant production systems. A meta-analysis was performed to assess overall efficacy and to identify factors that explain differences in product efficacy. In summary, efficacy of bleach products was greater for oomycetes and least for bacteria, and higher in water solutions than on solid substrates. These same factors explained 32 to 40% of the variation in using lower bleach doses and shorter contact times when treating irrigation water than treating solid substrates. Also, bleach was more effective at eliminating bacteria from metal versus porous surfaces. These results will provide guidance for directing new disinfestant research and help Extension personnel, crop advisors and agricultural and horticultural producers understand strengths and weaknesses of these products.

Technical Abstract: Bleach products containing hypochlorite are commonly used as disinfestants to eliminate non-fungal plant pathogens such as bacteria, oomycetes, and viruses, from production surfaces, plant surfaces, irrigation water, and produce dump tanks. While these products are useful, their effectiveness has been reported to vary in specific settings. A meta-analysis was conducted using 70 studies to assess the overall efficacy of hypochlorite against plant pathogenic bacteria, oomycetes and viruses and to identify factors that explain differences in product efficacy. Hypochlorite resulted in a significant (P < 0.0001) reduction in either disease intensity or propagule viability with a mean Hedges’ g standardized mean difference ( ) of 3.08, indicating that overall, hypochlorite treatments were highly effective. However, heterogeneity in g was significant (P < 0.0001) among studies. Specifically, 73.9% of the variance observed in g was attributed to true effects and an estimate of between study variability was high (t2 = 1.85). Random-effects meta-regression of continuous moderators showed that was significantly affected by contact time (ß = -0.002; P < 0.05) but not the dose of active ingredient. Similarly, random-effects analyses of categorical moderator variables showed that organism type significantly (P = 0.0135) affected efficacy of hypochlorite, while the target being treated did not affect efficacy (P = 0.2316). For bacteria, however, efficacy of hypochlorite was significantly higher (P = 0.0348) on metal than ‘Other’ target materials. Random-effects meta-regression indicated that organism type explained 28% of the variation in g associated with contact time (ß = -0.002; P = 0.0052), with oomycete having a significantly (P = 0.0063) larger than that of bacteria or viruses. When moderator effects were evaluated within oomycetes, 32% and 40% of the variation in dose was explained by the genus subgroups of Phytophthora and ‘Other’(P = 0.0158) and by the target subgroups of solution and ‘Other’, (P = 0.0299), respectively. Additionally, 41% of the variation in contact time was explained by the genus subgroups of Phytophthora and other (P = 0.0110). These results show that although the current recommended dose and contact time for commercial bleach products are generally expected to result in effective disinfestation, their efficacy against non-fungal plant pathogens is expected to be influenced by the organism type and target being treated.