Research Project: New Approaches to Enhance Fresh Fruit Quality and Control Postharvest Diseases

Location: Commodity Protection and Quality Research

2023 Annual Report

Objectives
Objective 1: Develop new preharvest approaches to enhance fruit quality and reduce postharvest diseases. • Sub-objective 1A: Evaluate the effects of anti-transpiration agents on water loss and fruit quality of blueberries. • Sub-objective 1B: Evaluate the effects of preharvest applications of plant disease-resistance elicitors on fruit quality and control of postharvest diseases of blueberries. Objective 2: Develop new postharvest technologies to maintain fruit quality and control postharvest diseases. • Sub-objective 2A: Evaluate generally-recognized-as-safe products or food additives applied as a postharvest treatment via different application technologies for control of postharvest fruit rot diseases of blueberries. • Sub-objective 2B: Develop coatings with/without antifungal products for reducing water loss and postharvest fruit rot diseases of blueberries. • Sub-objective 2C: Evaluate generally-recognized-as-safe products or food additives applied as a postharvest treatment via different application technologies for control of postharvest fruit rot diseases of table grapes.

Approach
The goal of this project is to develop new pre- and postharvest approaches to maintain postharvest quality and control postharvest fruit rots and thus extend storage and shelf life of fresh fruits. Field and laboratory experiments will be conducted to evaluate preharvest use of disease resistance inducers and anti-transpiration agents to increase blueberry fruit tolerance to postharvest diseases and enhance fruit quality. Fruit quality parameters, postharvest disease development, plant chemicals such as flavonoids and phenolic contents, and the activities of known defensive enzymes in the fruit will be analyzed to determine their relationships. Laboratory and cold storage experiments will be conducted to develop new postharvest approaches using generally-recognized-as-safe substances such as peroxyacetic acid and cold plasma-activated hydrogen peroxide and antimicrobial food additives such as natamycin applied via new postharvest application technologies to control postharvest fruit rots and retain fruit quality of blueberries and table grapes. Laboratory and cold storage experiments will also be conducted to develop coatings with/without antifungal products for reducing water loss and postharvest fruit rot diseases of blueberries.

Progress Report
In support of Sub-objective 1A, Parka™, the initial focus of the research for a field-applied blueberry fruit cuticle supplement that minimizes weight loss and preserves fruit quality, was found to have no impact on any fruit quality parameters and unworthy of further experimentation. The search continues for cuticle supplement alternatives. In support of Sub-objective 1B, research was conducted to evaluate effects of plant resistance inducers applied in the field on postharvest fruit rot diseases and fruit quality of blueberries. Benzothiadiazole (Actigard), potassium silicate (Sil-MATRIX), and a nontreated control (water) were applied to blueberry plants of variety Jewel in a research field four times during the growing season. Blueberry fruit were harvested at commercial maturity. Part of the fruit was used to test its quality. Another part of the fruit was used to assess development of postharvest diseases during cold storage. Upon completion of cold storage at 0 degrees C for four weeks, fruit will be evaluated for decay development. In support of Sub-objective 2A, research continued to evaluate effectiveness of postharvest treatment with natamycin applied using an electrostatic spray system (ESS) in comparison with a conventional sprayer for control of postharvest fruit rot diseases of blueberries. Four concentrations of natamycin were used for the ESS application in comparison with a conventional spray method at two different concentrations. Two non-treated controls (water applied by a conventional sprayer and an ESS) were also included. The experiment was conducted on two blueberry varieties, Jewel and San Joaquin. Upon completion of storage at 0 degrees C for four weeks, decay development will be evaluated in the treated and nontreated fruit. In support of Sub-objective 2A, research continued to evaluate effectiveness of natamycin as a postharvest fogging treatment to control postharvest fruit rots of blueberries. Commercially harvested blueberry fruit were used for this experiment. Natamycin and a nontreated control (water) were applied using a fogger in a temperature-controlled environment room at 15 degrees C. Blueberry fruit were placed in plastic totes with five totes per layer for a total of 65 totes that were palletized. The palletized blueberries were fogged with five gallons of natamycin solution for 40 min, followed by 20 min of waiting time for fogged droplets to settle down. The control treatment was fogged with water. Fruit were then packed into 6-oz clamshells and stored at 0-1 degrees C for four weeks. Fruit rots will be evaluated after the cold storage period. Fruit sampled from various localities within the pallet will also be analyzed for natamycin residue on the fruit. In support of Sub-objective 2B, all research results on blueberry postharvest coatings were organized and published. Research findings revealed that none of the coatings tested were suitable for commercial use due to lack of effectiveness in the preservation of blueberry quality in storage and damaging effect on surface appearance. Chitosan was somewhat useful in reducing decay but was harmful to quality in other ways. Further research on alternative means to reduce weight loss and maintain blueberry quality is underway. In support of Sub-objective 2C, research was conducted to evaluate effectiveness of natamycin as a postharvest fogging treatment to control postharvest fruit rots of table grapes. Organically grown freshly harvested table grapes, variety Scarlet Royal, were used in this experiment. Four 4-lbs clamshells of table grapes were placed in a plastic fruit tote. Totes were placed on a wooden pallet. One tote layer consisted of six totes. A total of 10 tote layers were placed on the pallet. Two pallets of fruit were prepared for the experiment, one pallet for the nontreated water control and the other for natamycin treatment. Grapes in the pellet were fogged with three gallons of natamycin solution for about 40 min, followed by a 20-min of waiting time for fogged droplets to settle down. Three gallons of water containing surfactant was used as control. After the treatment, grapes were packed into 4-lbs clamshells. Two sets of samples were prepared: one set of samples was stored for four weeks at 0-1 degrees C, and the other set was stored for four weeks at 0-1 degrees C, followed by a two-day storage at 20 degrees C to simulate retail conditions. After the four-week cold storage, grapes fogged with natamycin had significantly lower percentage of rots compared to the grapes that were fogged with water. Natamycin fog treatment reduced the incidence of fruit rots from 11.9 percent (%) in the non-treated control to 6.7% in the natamycin-treated fruit. After the four-week cold storage followed by a two-day period at 20 degrees C, the difference between the two treatments became more pronounced. Natamycin treatment significantly reduced number of decayed grapes compared to the control, with incidence of fruit rots reduced from 41.3% in the control to 15.9% in the natamycin-treated fruit. In support of Objective 2, further work was conducted to determine if reducing the vent size in containers commonly used to market blueberries could be a viable method to reduce weight loss in storage. Low vent clamshells greatly reduce water loss from blueberries but can increase decay if disease pressure is high. Ongoing fumigation experiments were established to address this issue using sulfur dioxide or a natamycin dip to inhibit decay prior to packaging the fruit. In support of Objective 2, research on the preservation of muscat flavor in table grapes using low oxygen, high carbon dioxide, or a combination of both continued. A large experiment indicated that altered atmospheres can be used to maintain muscat flavor for at least nine weeks. Additionally, the amount of decay is reduced by at least 50% as compared to air when high carbon dioxide is included. Quantities of muscat flavor components largely followed the sensory results and indicate the likely reason that the preservation occurs. In support of Objective 2, an investigation was initiated to determine the degree of flavor loss that occurs during storage and marketing of blueberries and define the factors causing it. Key flavor components potentially involved in flavor loss remain to be fully determined to be able to quantify changes that occur because of storage. This research also involves sensory evaluation during the blueberry season.

Accomplishments
1. Grape flavor can be preserved in storage. Muscat flavor in grapes is rapidly lost in storage and is a major issue with this type of grape. ARS researchers in Parlier, California, determined that this loss can almost totally be prevented by storage in low oxygen combined with high carbon dioxide. Flavor protection occurs because key flavor aromas are not lost. Another benefit of treatment is the reduction of decay by more than 50 percent as compared to air storage. This offers a potential means to protect muscat grape flavor and quality prior to marketing.

2. Postharvest use of natamycin to control fruit rots in blueberries. Postharvest fruit rots are a key factor limiting the storage and shelf life of fresh blueberries. Control of postharvest fruit rot diseases is important to the domestic and international marketing of fresh blueberries, but no products have been registered in the United States specifically for control of postharvest fruit rots. ARS researchers in Parlier, California, evaluated natamycin as a postharvest dipping or spraying treatment for control of postharvest fruit rots of blueberries. Natamycin was highly effective in controlling fruit rots and did not adversely affect fruit quality. Natamycin is commonly used as a food additive in the food industry and is considered a biofungicide. The results showed that natamycin is a promising postharvest tool to reduce postharvest fruit rots and maintain fruit quality of fresh blueberries, and the data are used to support a pending registration of natamycin for postharvest use on blueberries.

Review Publications
Afifi, M., Rezk, A., Obenland, D.M., El-kereamy, A. 2023. Vineyard light manipulation and silicon enhance ethylene-induced anthocyanin accumulation in red table grapes. Frontiers in Plant Science. 14. Article 1060377. https://doi.org/10.3389/fpls.2023.1060377.
Obenland, D.M., Arpaia, M. 2023. Managing postharvest storage issues in ‘Shiranui’ mandarin. HortTechnology. 33(1):118-124. https://doi.org/10.21273/HORTTECH05133-22.
Obenland, D.M., Leyva-Gutierrez, F., Wang, T. 2022. Investigations into determinants of blueberry coating effectiveness. Foods. 12(1). Article 174. https://doi.org/10.3390/foods12010174.
Naegele, R.P., Abdelsamad, N.A., DeLong, J.A., Saito, S., Xiao, C., Miles, T. 2022. Fungicide resistance and host influence on population structure in Botrytis spp. from specialty crops in California. Phytopathology. 112(12):2549-2559. https://doi.org/10.1094/PHYTO-03-22-0070-R.
Wang, F., Saito, S., Xiao, C. 2023. Fungicide resistance of Alternaria alternata and A. arborescens isolates from mandarin fruit and its influence on control of postharvest Alternaria rot. Plant Disease. 107(5):1538-1543. https://doi.org/10.1094/PDIS-09-22-2157-RE.