Research Project: Integrate Pre- and Postharvest Approaches to Enhance Fresh Fruit Quality and Control Postharvest Diseases

Location: Commodity Protection and Quality Research

2017 Annual Report

Objectives
Objective 1: Integrate pre- and postharvest approaches to enhance fruit flavor quality and enable commercial methods to extend postharvest life of fresh fruit. • Sub-objective 1A: Identify factors influencing the development of postharvest off-flavor formation in mandarins. • Sub-objective 1B: Develop pre- and postharvest integrated practices using reduced-risk or generally-recognized-as-safe substances and advanced packaging technologies to control postharvest diseases and maintain fruit quality of blueberries. • Sub-objective 1C: Develop pre- and postharvest integrated practices using reduced-risk or generally-recognized-as-safe substances to control postharvest diseases and maintain fruit quality of table grapes. Objective 2: Enable new commercial postharvest methods to remove or reduce fungicide residues on fresh fruit. • Sub-objective 2A: Develop postharvest treatments with generally-recognized-as-safe substances to remove or reduce fungicide residues on blueberries.

Approach
The goal of this project is to maintain/improve fruit quality and prolong storage and shelf life of fresh fruits. The emphasis is on the integration of pre- and postharvest practices using reduced-risk fungicides or substances that are generally recognized as safe for decay control and fruit quality preservation. Field and laboratory experiments will be conducted on different varieties to identify biochemical, physiological and anatomical factors that influence off-flavor development in mandarin citrus after harvest. Field and cold storage experiments will be conducted to evaluate various pre- and postharvest practices using reduced-risk or generally-recognized-as-safe substances and advanced packaging technologies to control postharvest diseases and maintain fruit quality of blueberries and table grapes. Initially effective individual pre- and postharvest practices will be identified, and in the later phase of the project integrations of effective pre- and postharvest practices will be developed and evaluated. The effects of postharvest fumigation treatments with generally-recognized-as-safe substances on fungicide residues on blueberry fruit will be evaluated, and effective treatments will be developed as mitigation measures for removal or reduction of fungicide residues on blueberry fruit.

Progress Report
In research under Sub-objective 1A, the permeability of the peel of mandarins to oxygen decreased and the rate of respiration increased as the fruit became more mature. These two factors may be responsible to a large extent for the lower internal oxygen level that is seen in more mature fruit. Fruit toward the end of the harvest season were highly susceptible to off-flavor formation during storage, likely a consequence of insufficient oxygen inside the fruit. Desiccation of the peel, as might occur during degreening of the fruit, was found to have very little influence on the permeability of the peel to oxygen until the desiccation was quite severe. In research under Sub-objective 1B, on the blueberry fruit that were treated with various products including organic compatible products before harvest, polyoxin D zinc salt (OSC), peracetic acid (PAA), and the biocontrol agent Aureobasidium pullans (Botector) reduced the incidence of decay resulting from natural infections by 54%, 28%, and 38% compared to the nontreated control. Fungicides Elevate and Switch showed significant residual activity against the gray mold fungus on wounded fruit inoculated with the pathogen, whereas Switch and the mixture of Luna Tranquility exhibited significant residual activity against Alternaria alternata. Postharvest fumigation of blueberry fruit with continuous ozone at concentrations ranging from 0 to 1 parts per million (ppm) during cold storage was evaluated in research under Sub-objective 1B. Ozone concentrations of 0.5 and 1 ppm significantly reduced the incidence of Alternaria rot compared to other treatments. Ozone concentrations lower than 0.5 ppm were not effective in controlling Alternaria rot. Ozone at 0.1 ppm or higher significantly suppressed the spread of the gray mold among the fruit compared to the nontreated control. In research under Sub-objective 1C, fungicide rotation programs for control of postharvest gray mold in stored table grapes was evaluated. In comparison with the non-treated control, all six preharvest fungicide rotation programs (rotation among Elevate, Luna Experience and Switch) significantly reduced the fruit-to-fruit spread of gray mold within grape clusters during storage and subsequent two days at room temperature after cold storage. All fungicide rotation programs exhibited residual protection of grape berries. On the grapes that were wounded and inoculated with gray mold spores after harvest, all fungicide programs significantly reduced the decay size on the fruit compared to the non-treated control, though only the treatment with Luna, Elevate and Switch rotation significantly reduced the incidence of gray mold (percent of fruit decayed). It appeared that rotation programs with Elevate or Switch as a last spray in the programs applied just before harvest seemed to be more effective than other rotation programs. Further research is still needed to confirm this finding. Effects of ozone fumigation on fungicide residues on blueberry fruit were evaluated in research under Sub-objective 2A. Organic blueberry fruit were treated in the lab with various fungicides subjected to ozone fumigation at 2000 ppm or 5000 ppm for two hours. Ozone fumigation did not cause visible phytotoxicity on the fruit compared to the nonfumigated control. Ozone treatments significantly reduced fungicide residues on blueberry fruit, except captan. Residue reduction rate was 76.3-77.6%, 74.5-78.3%, 30.0-42.1% and 40.5-43.2% for azoxystrobin, cyprodinil, fenhexamid and fludioxonil, respectively, compared to those on the fruit that were not treated with ozone.

Accomplishments
1. Harvest date influences internal oxygen concentration in mandarins. Mandarins can develop poor flavor in storage that is disliked by consumers but the factors influencing this problem are poorly understood. ARS researchers in Parlier, California harvested mandarins at various time points from early to late season and observed low internal oxygen concentrations and poor flavor in late season fruit. A potential cause for this was found to be lower peel oxygen permeability and a higher rate of respiration in late versus early season fruit. This finding helps enable a further understanding of how off-flavor occurs and enhances the ability to develop means to prevent it.

2. Multiple fungicide resistance discovered in pathogen pest of blueberries. Gray mold caused by the fungal pathogen Botrytis cinerea is a major postharvest fruit rot disease of blueberries. ARS researchers in Parlier, California determined the presence of various fungicide-resistant phenotypes in the pathogen populations. Research showed that some key fungicides used in the field failed to control gray mold incited by respective resistant strains. These research findings provide insights on the judicious use of fungicides in the field and necessitate the development of pre- and postharvest alternatives to synthetic fungicides for control of fruit rots on blueberries.

Review Publications
Saito, S., Michailides, T.J., Xiao, C. 2016. Fungicide resistance profiling in Botrytis cinerea populations from blueberries in California and Washington and their impact on control of gray mold. Plant Disease. 100(10):2087-2093. doi: 10.1094/PDIS-02-16-0229-RE.
Wiseman, M., Dugan, F.M., Xiao, C. 2016. Potential hosts for Lambertella corni-maris and Phacidium lacerum within the family Rosaceae. Plant Health Progress. 17:128-129.
Aguilar, C.G., Mazzola, M., Xiao, C. 2017. Timing of apple fruit infection by Neofabraea perennans and Neofabraea kienholzii in relation to bull’s-eye rot development in stored apple fruit. Plant Disease. 101:800-806. doi: 10.1094/PDIS-11-16-1637-RE.
Jain, A., Paz, J., Obenland, D.M., Rodriguez, K., Prakash, A. 2017. Effect of phytosanitary irradiation on the quality of two varieties of pummelos (Citrus maxima (Burm.) Merr.). Scientia Horticulturae. 217:36-37. doi:10.1016/j.scienta.2017.01.029.
Ornelas-Paz, J., Meza, M., Obenland, D.M., Rodriguez, K., Jain, A., Thornton, S., Prakash, A. 2017. Effect of phytosanitary irradiation on the postharvest quality of Seedless Kishu mandarins (Citrus kinokuni mukakukishu). Food Chemistry. 230:712-720. https://doi.org/10.1016/j.foodchem.2017.02.125.