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

Location: Commodity Protection and Quality Research

2019 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
Under Objective 1, a sensory descriptive panel using 10 trained panelists was developed to characterize avocado flavor in detail. The panelists were trained over a period of months to recognize different flavors and textures potentially important to determining the avocado eating experience. Two avocado varieties (Hass and Gem) were harvested over the entire season to provide differing avocado flavor qualities. Samples from each harvest were tasted and characterized by the descriptive panel as well as by a consumer panel that consisted of at least 70 panelists each time. Characterization of the harvested samples for chemical constituents, such as fatty acids and volatiles, is being conducted to attempt to relate flavor as described by both the descriptive and consumer sensory panels to the composition of the avocado. Under Sub-objective 1B, integrated approaches consisting of preharvest reduced-risk fungicides and postharvest continuous ozone fumigation at low doses (0.3 and 1 parts per million (ppm)) for control of postharvest diseases of blueberries were conducted. Fungicides Switch (a mixture of fludioxonil and cyprodinil) and fenhexamid were applied to the fruit before harvest. After harvest, part of the fruit was inoculated with either Alternaria alternata or Botrytis cinerea, and part of the fruit that was not artificially inoculated was used for assessing treatment effects on decay resulting from natural infections. Fruit were then stored at 0 degrees Celsius (°C) either in air or continuous ozone at 0.3 or 1 ppm. Both fungicide and ozone treatments significantly reduced incidence and severity of gray mold on inoculated fruit. Ozone significantly reduced the fruit-to-fruit spread of gray mold, and the mixture of fludioxonil and cyprodinil significantly reduced the spread of gray mold but not fenhexamid. Ozone alone did not significantly reduce the incidence and severity of Alternaria rot on inoculated fruit. The mixture of fludioxonil and cyprodinil significantly reduced incidence and severity of Alternaria rot. Under Sub-objective 1B, preharvest reduced-risk fungicides in combination with postharvest sulfur dioxide-emitting pads (either single-stage slow releasing or dual-stage releasing) for control of postharvest diseases in blueberries were conducted. Fungicides Switch and fenhexamid were applied to the fruit before harvest. After harvest, part of the fruit was inoculated with either Alternaria alternata or Botrytis cinerea, and part of the fruit that was not artificially inoculated was used for assessing treatment effects on natural infections. Fruit were packed into clamshells and placed in cardboard boxes, and one sulfur dioxide-releasing pad was placed on each of the two layers of clamshells in the box. Clamshells were wrapped with a plastic bag in each box. Fruit were then stored at 0° Celsius (C) for decay development. The slow sulfur dioxide-releasing pad did not provide satisfactory control of gray mold and Alternaria rot on inoculated fruit, but the dual sulfur dioxide-releasing pad effectively controlled both diseases. Sulfur dioxide-releasing pads and the fungicide Switch significantly reduced fruit rots resulting from natural infections on fruit. However, bleaching was evident on the fruit treated with the dual sulfur dioxide-releasing pad. Preharvest Switch, in combination with the postharvest slow sulfur dioxide-releasing pad, appeared to be a promising approach for control of fruit rots without compromising fruit quality. Under Sub-objective 1C, preharvest reduced-risk fungicide rotation programs in combination with postharvest continuous ozone fumigation for control of postharvest diseases in table grapes were conducted. Preharvest fungicide-rotation programs included Luna Experience, Switch, and Elevate; Luna Experience, Elevate, and Switch; Switch, Luna Experience, and Elevate; Elevate, Luna Experience, and Switch; and a nontreated. Fruit were harvested at commercial maturity. After harvest, part of the fruit was stored under 0.1 ppm continuous ozone, and another part of the fruit was stored in regular air at 0C for five weeks, at which time fruit rots on stored grapes were evaluated. The incidence of gray mold resulting from natural infections was very low, and there were no significant differences in rachis appearance and incidence of gray mold among the fungicide-rotation treatments. Both fungicide treatments and ozone fumigation significantly reduced the number of infected berries resulting from fruit-to-fruit spread via mycelium of gray mold. There were no significant interactions between preharvest fungicide treatments and postharvest ozone fumigation. However, ozone fumigation had negative effects on rachis appearance.

Accomplishments
1. Fumigation with phosphine does not harm citrus quality. Fumigation with methyl bromide may not be possible in the future so a replacement is urgently needed to maintain the export of citrus to countries that require a quarantine treatment. ARS researchers in Parlier, California, tested the tolerance of mandarins, navel and Valencia oranges, lemons and grapefruit to phosphine fumigation and found that quality is not adversely affected by the treatment. This quarantine treatment was superior to both methyl bromide fumigation and cold treatment that sometimes damaged the peel surface. This research gives confidence in the ability to control insect pests and continue citrus exports in the absence of methyl bromide.

Review Publications
Sikdar, P., Mazzola, M., Xiao, C. 2019. Genetic and pathogenic characterization of Phacidiopycnis washingtonensis from apple and Pacific madrone from western United States. Phytopathology. 109(3):469-479. https://doi.org/10.1094/PHYTO-10-17-0358-R.
Saito, S., Xiao, C. 2018. Fungicide resistance in Botrytis cinerea populations in California and its influence on control of gray mold on stored Mandarin fruit. Plant Disease. 102(12):2545-2549. https://doi.org/10.1094/PDIS-05-18-0766-RE.
Obenland, D.M., Arpaia, M. 2018. Effect of harvest date on off-flavor development in mandarins following postharvest wax application. Postharvest Biology and Technology. 149:1-8. https://doi.org/10.1016/j.postharvbio.2018.11.010.
Saito, S., Michailides, T.J., Xiao, C. 2019. Fungicide-resistant phenotypes in Botrytis cinerea populations and their impact on control of gray mold on stored table grapes in California. European Journal of Plant Pathology. 154(2):203-213. https://doi.org/10.1007/s10658-018-01649-z.
Aguilar, C., Mazzola, M., Xiao, C. 2019. Timing of perennial canker development in apple trees caused by Neofabraea perennans and Neofabraea kienholzii. Plant Disease. 103(3):555-562. https://doi.org/10.1094/PDIS-06-18-0935-RE.
Wang, J., Guo, L., Xiao, C., Zhu, X. 2018. Detection and identification of six Monilinia spp. causing brown rot using TaqMan real-time PCR from pure cultures and infected apple fruit. Plant Disease. 102(8):1527-1533. https://doi.org/10.1094/PDIS-10-17-1662-RE.