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

Location: Commodity Protection and Quality Research

2020 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
This is the final report for the project 2034-43000-039-00D which was terminated in May 2020 and has been replaced by the new project 2034-43000-041-00D, "New Approaches to Enhance Fresh Fruit Quality and Control Postharvest Diseases." Substantial results were realized over the five years of the project. Progress was made on all objectives and their sub-objectives, all of which fall under National Program 306, Component I, Foods. Progress on this project focuses on Problem Statement 1A, define, measure, preserve/enhance/reduce attributes that impact quality and marketability. Under Sub-objective 1A, we made significant progress in identifying factors influencing the development of postharvest off-flavor formation in mandarins. We determined that genotypic differences exist in mandarins in the propensity to develop off-flavor during storage and further that the mechanism by which this loss in flavor quality occurs may not be as previously thought. We determined that time of season was a critical factor in determining if off-flavor will occur in some mandarin types and that flavor will remain excellent following storage if harvest occurs at the right time of year. We also reported that Mucor rot caused primarily by the fungus M. piriformis is an emerging postharvest fruit rot disease affecting stored mandarin citrus fruit, and we developed postharvest treatments that are effective in controlling Mucor rot in stored mandarin fruit. Under Sub-objective 1B, we made significant progress in developing 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. We determined that gray mold caused by Botrytis cinerea and Alternaria rot caused by A. alternata and A. aborescens are the major postharvest fruit rot diseases affecting blueberries in California. These findings provide the basis for developing control methods to target relevant pathogens for blueberries. We determined that resistance to multiple different modes-of-action fungicides is widespread in the Botrytis cinerea populations from blueberry in California, resulting in the failure of disease control. However, the mixture of fludioxonil and cyprodinil significantly reduced gray mold and Alternaria rot of blueberries. These findings indicated chemical control of gray mold caused by B. cinerea is not a sustainable approach because of evolving fungicide resistance development in the pathogen populations and suggested developing sustainable approaches as alternatives to conventional fungicides for controlling postharvest gray mold in fresh fruits is necessary. We determined that postharvest treatments with continuous ozone fumigation at low concentrations significantly reduced postharvest fruit rots and limited spread of gray mold among blueberry fruit during cold storage. These treatments provide new tools for control of postharvest fruit rot diseases of blueberries. We also made significant progress in the use of sulfur dioxide-emitting packaging technologies to control postharvest fruit rots and maintain fruit quality of blueberries. We determined that sulfur dioxide-emitting packaging liners, sheets, or bags with modified atmosphere capability significantly reduced postharvest fruit rots, suppressed the spread of gray mold, and prevented weight loss of the fruit compared to the control. Our data supported the registration of sulfur dioxide-emitting packaging materials for emergency use in California on blueberries for export. We also determined that the preharvest fungicide mixture of fludioxonil and cyprodinil in combination with a postharvest single-stage, sulfur dioxide slow-releasing pad, appeared to be an effective pre- and postharvest integrated approach for control of fruit rots and maintenance of fruit quality of blueberries. Under Sub-objective 1C, we made significant progress in developing 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. We determined that resistance to multiple different modes-of-action fungicides is widespread in the Botrytis cinerea populations from table grape, resulting in the failure of disease control, and identified fungicides that can be used as a preharvest treatment to reduce postharvest gray mold in stored table grapes. These findings indicated chemical control of gray mold caused by B. cinerea is not a sustainable approach because of evolving fungicide resistance development in the pathogen populations. We also determined that both preharvest fungicide treatments and postharvest ozone fumigation significantly reduced fruit-to-fruit spread of gray mold in stored table grapes. There were no synergistic effects between preharvest fungicide treatments and postharvest ozone fumigation; however, ozone fumigation can have negative effects on rachis appearance. This research provides insights into the use of these alternative approaches on table grapes. Under Objective 2, we made progress in the use of postharvest ozone fumigation to remove or reduce fungicide residues on fresh fruit. We determined that fumigation with ozone at 2000 parts per million (ppm) or 5000 ppm for two hours significantly reduced fungicide residues on blueberry fruit, except for captan, and did not cause visible phytotoxicity on the fruit compared to the nonfumigated control.

Accomplishments
1. Determinants of avocado flavor to improve future avocado varieties. Avocados are a valuable crop, but what causes avocados to have poor or good taste is not well understood. ARS researchers in Parlier, California, utilized both trained and consumer sensory panels to define those aspects of flavor that have the most importance. This was the first time a trained panel had ever been utilized to study avocado flavor differences in detail. Furthermore, chemical analyses were performed to define compounds that influence flavor. Information from this study will be useful in the development of new, better tasting avocado varieties in the future.

2. Pre- and postharvest approaches control postharvest fruit rots of blueberries. Postharvest fruit rots are a key factor limiting the storage and shelf life of fresh blueberries. Control of postharvest fruit rot diseases are important to the domestic and international marketing of fresh blueberries, but no products have been registered specifically for control of postharvest fruit rots. ARS researchers in Parlier, California, tested reduced-risk fungicides as a preharvest treatment and a postharvest continuous ozone fumigation for control of fruit rots on blueberries and found that the mixture of fludioxonil and cyprodinil significantly reduced gray mold and Alternaria rot, the two most important postharvest diseases of blueberries grown in California. Continuous ozone fumigation at low doses significantly reduced gray mold and its fruit-to-fruit spread. These treatments provide new tools for control of postharvest fruit rot diseases of blueberries.

3. Preharvest fungicides plus postharvest sulfur dioxide-emitting pads control postharvest fruit rots of blueberries. Postharvest fruit rots and water loss limit the storage and shelf life of fresh blueberries. ARS researchers in Parlier, California, tested reduced-risk fungicides as a preharvest treatment in combination with the use of sulfur dioxide-emitting pads in cartons to control postharvest fruit rots and maintain fruit quality of fresh blueberries. Sulfur dioxide-emitting pads and the fungicide mixture of fludioxonil and cyprodinil significantly reduced fruit rots. However, bleaching was evident on the fruit treated with the dual-stage sulfur dioxide releasing pad. Preharvest fungicide mixture of fludioxonil and cyprodinil, in combination with the postharvest single-stage, sulfur dioxide slow-releasing pad, appeared to be a promising approach for control of fruit rots without compromising fruit quality.

4. Use of preharvest reduce-risk fungicides and postharvest ozone fumigation control postharvest rots of table grapes. Postharvest rots limit the storage and shelf life of table grapes. Control of postharvest rots of table grapes has long relied on postharvest fumigation with sulfur dioxide, but alternatives are needed because of concerns about its residue. ARS researchers in Parlier, California, tested preharvest reduced-risk fungicide rotation programs in combination with postharvest continuous ozone fumigation for control of postharvest diseases in table grapes and found that both fungicide treatments and ozone fumigation significantly reduced fruit-to-fruit spread of gray mold, the major postharvest rot of table grapes. There were no synergistic effects between preharvest fungicide treatments and postharvest ozone fumigation; however, ozone fumigation can have negative effects on rachis appearance. This research provides insights into the use of these alternative approaches on table grapes.

Review Publications
Saito, S., Obenland, D.M., Xiao, C. 2020. Influence of sulfur dioxide-emitting polyethylene packaging on blueberry decay and quality during long-term storage. Postharvest Biology and Technology. 160. Article 111045. https://doi.org/10.1016/j.postharvbio.2019.111045.
Naegele, R.P., Delong, J.A., Saito, S., Xiao, C. 2020. Population genetics and fungicide resistance of Botrytis cinerea on Vitis and Prunus spp. in California. Phytopathology. 110(3):694-702. https://doi.org/10.1094/PHYTO-09-19-0362-R.
Kheshti, N., Melo, A., Bacquero, A., Obenland, D.M., Prakash, A. 2019. Physiological response of ‘Fuji’ apples to irradiation and the effect on quality. Journal of Radiation Physics and Chemistry. 165. https://doi.org/10.1016/j.radphyschem.2019.108389.
Saito, S., Wang, F., Xiao, C. 2020. Efficacy of Natamycin against gray mold of stored mandarin fruit caused by isolates of Botrytis cinerea with multiple fungicide resistance. Plant Disease. 104(3):787-792. https://doi.org/10.1094/PDIS-04-19-0844-RE.