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

Location: Commodity Protection and Quality Research

2021 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, field application of the pre-harvest fruit cuticle supplement Parka was applied to two varieties in April and May of 2021. The fruit from these applications are currently in cold storage waiting evaluation. In support of Sub-objective 1B, a field experiment was conducted to evaluate effects of preharvest applications of plant resistance inducers 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 four times during the growing season. Blueberry fruit were harvested at commercial maturity. Part of the fruit were used to test fruit quality and part of the fruit were used to test development of postharvest diseases during cold storage. After cold storage for four weeks, potassium silicate significantly reduced incidence of fruit rots resulting from natural infections by 46%, while Benzothiadiazole did not reduce fruit rots compared to the water control. Determination of fruit quality parameters is still in progress. The results showed that potassium silicate is a promising preharvest treatment to enhance fruit tolerance to fruit rot diseases in blueberries. In support of Objective 1, in a collaboration with a scientist of the University of California, various preharvest sprays were evaluated for their ability to reduce mandarin rind disorder. It was found that fruit in the outer canopy were more susceptible and that there were clear varietal differences in the degree of the disorder. Spraying at color break with 2,4-dichlorophenoxyacetic acid, gibberellic acid or VaporGard acted to reduce damage. Gibberellic acid was the most effective but also harmed quality by inhibiting color development. Further refinement in the concentration applied is ongoing. In support of Sub-objective 2A, an experiment was conducted to evaluate the effectiveness of natamycin (a biofungicide) for control of postharvest diseases of blueberries. Natamycin was applied as either a dipping or a spraying treatment, and water was used as a control. Blueberry fruit treated with natamycin at one-quarter, one-half and full label rates were stored at 0C for four weeks and then disease development was assessed. Fruit quality was also determined prior to the treatment and after cold storage. Natamycin, even at one-quarter of the label rate, was highly effective in controlling gray mold caused by Botrytis cinerea, a major postharvest disease of blueberries. Natamycin also reduced overall fruit decay resulting from natural infections and had no adverse effect on fruit quality during the storage. Our results suggest that natamycin can be a promising tool to control postharvest fruit rot diseases of stored blueberry while maintaining fruit quality. In support of Sub-objective 2A, an experiment was conducted to evaluate effectiveness of a postharvest treatment with natamycin applied using an electrostatic sprayer in comparison with a conventional sprayer for control of postharvest fruit rot diseases of blueberries. Two non-treated controls (water applied by a conventional sprayer and an electrostatic sprayer) were also included. The experiment was conducted on two varieties, Jewel and San Joaquin. Fruit were stored at 0C for four weeks at which time decay development was evaluated. Natamycin significantly reduced fruit rots resulting from natural infections regardless of application methods compared to the water control. There were over 80% and over 62% reduction in percentage of decayed berries on Jewel and San Joaquin, respectively. On the fruit inoculated with Botrytis cinerea or Alternaria alternata and treated with natamycin, both application methods significantly reduced gray mold caused by B. cinerea and Alternaria rot caused by A. alternata compared to the controls. The results showed that electrostatic spraying of natamycin is a promising treatment to deliver a low volume spray treatment for control of postharvest fruit rots in blueberries. In support of Sub-objective 2A, a small chamber experiment was conducted to evaluate effectiveness of ionized hydrogen peroxide applied as a fog treatment using a specialized equipment based on the Binary Ionization Technology (BIT) by TOMIMIST for control of postharvest fruit rot diseases of blueberries. Two rates of ionized hydrogen peroxide (0.35% and 7.8% BIT hydrogen peroxide) and water control were included. After treatment, fruit were stored at 0C for four weeks and fruit rots were then assessed. Hydrogen peroxide treatments at 7.8% significantly reduced percentage of decayed berries by 38.0% relative to the nontreated control. However, phytotoxic effects were observed on blueberries treated with 7.8% hydrogen peroxide. Hydrogen peroxide at 0.35% did not cause phytotoxic effects on treated fruit but it did not significantly reduce fruit rots compared to the nontreated control. On the inoculated fruit with Botrytis cinerea or Alternaria alternata and treated with ionized hydrogen peroxide, only 7.8% hydrogen peroxide significantly reduced gray mold caused by B. cinerea. Ionized hydrogen peroxide treatments did not significantly reduce Alternaria rot compared to the control. In support of Sub-objective 2A, an experiment was conducted to test peroxyacetic acid (PAA) for control of postharvest fruit rots of blueberries. Two application methods (spraying and dipping) at two rates (24 and 85 PPM based on the label) of peroxyacetic acid were tested on two cultivars ‘Snowchaser’ and ‘Jewel’. Blueberry fruit were harvested at commercial maturity, treated with PAA, and then stored at 0C for four weeks. For ‘Snowchaser’, the percentage of decayed berries was reduced by 22.6% and 66.5% for low and high concentrations of PAA by dipping, respectively, while the percentage of decayed berries was reduced by 42.7% and 68.6% for low and high concentrations of PAA by spraying, respectively. Overall, disease incidence was very low for ‘Jewel’ in 2020, but a significant reduction of percentage of decayed fruit was observed when the high concentration of PAA was applied by dipping. PAA is considered a generally recognized as a safe substance. The results showed PAA is a promising postharvest tool to reduce postharvest fruit rots and maintain fruit quality of fresh blueberries. In support of Sub-objective 2A, an experiment was conducted to evaluate hydrogen peroxide for control of postharvest diseases of blueberries. Sachets that release hydrogen peroxide were placed in a cold storage room to test hydrogen peroxide fumigation on postharvest rots of blueberries. After four weeks of storage, there were no significant differences in fruit rots of blueberries between the hydrogen peroxide fumigation and nontreated control. In support of Sub-objective 2B, blueberries from two varieties were coated with various formulations of chitosan with and without oleic acid, or Semperfresh immediately after harvest and stored for either three or six weeks at 1C to determine if the coatings could be used to improve postharvest quality. In addition, commercially packaged fruit were tested with similar treatments. Moisture loss, the attribute of greatest interest in the test, was not reduced by any of the coatings, nor were any of the other quality parameters positively affected. In the case of Semperfresh, spraying or dipping treatments were of equal effectiveness, although it was found that excessive handling during the coating process was deleterious. Further testing, using additional coatings, is underway this season. In support of Sub-objective 2C, experiments were conducted on table grape variety Scarlet Royal to evaluate the effectiveness of natamycin (a biofungicide) for control of postharvest diseases of table grapes. Natamycin was applied as either a dipping or a spraying treatment, and water was used as a control. After cold storage for four weeks and subsequently two additional days at room temperature, the dipping treatment significantly reduced fruit rots resulting from natural infections from 41% in the nontreated control to 0.3% in the treated fruit, and the spraying treatment significantly reduced fruit rots from 33% in the nontreated control to 0.6% in the treated fruit. Also, natamycin treatments did not negatively affect the appearance of rachis and there were no significant differences in the firmness, soluble solid, soluble acidity of Scarlet Royal grapes, suggesting that natamycin treatments did not affect fruit quality regardless of application methods. In a separate experiment, fruit inoculation tests were conducted to determine the effect of different concentrations of natamycin on the control of gray mold caused by Botrytis cinerea. Natamycin at full, one-half, one-quarter, one-eighth and one-sixteenth recommended label rates significantly reduced disease incidence and severity on the table grapes inoculated with Botrytis isolates, regardless of application method and incubation temperature. The one-quarter rate of natamycin reduced disease incidence by 96.4% to 100% and 96.6% to 98.3% for dipping and spraying methods, respectively. The reduction of disease severity by the on-eighth and one-quarter rate of natamycin was comparable to those by one-half or full rate of natamycin. Those results suggested that one-quarter rate of natamycin may be enough to control gray mold on detached table grape berries.

Accomplishments
1. New postharvest treatments to control 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 natamycin (a food additive and biofungicide) for control of fruit rots on blueberries and found that natamycin applied as either a dipping or spraying treatment significantly reduced Alternaria rot, a major postharvest fruit rot disease of blueberries grown in California. Natamycin treatments provide new tools for control of postharvest fruit rot diseases and maintenance of fruit quality of blueberries.

Review Publications
Wang, F., Saito, S., Michailides, T.J., Xiao, C. 2021. Postharvest use of Natamycin to control alternaria rot on blueberry fruit caused by Alternaria alternata and A. arborescens. Postharvest Biology and Technology. 172. Article 111383. https://doi.org/10.1016/j.postharvbio.2020.111383.
Hausch, B.J., Arpaia, M., Kawagoe, Z., Walse, S.S., Obenland, D.M. 2020. Chemical characterization of two California-grown avocado varieties (Persea americana Mill.) over the harvest season with an emphasis on sensory-directed flavor analysis. Journal of Agricultural and Food Chemistry. 68(51):15301-15310. https://doi.org/10.1021/acs.jafc.0c05917.
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.