Location: Commodity Protection and Quality Research
2022 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 of blueberries. Weight loss, decay, shrivel, marketability, firmness, soluble solids (sugar) and acidity after harvest were unchanged by the application of Parka. The ineffectiveness of the pre-harvest fruit cuticle supplement under the conditions tested indicates that further research with this material is unwarranted. Additional products suitable for this purpose have not yet been identified.
In support of Sub-objective 1B, research continued to evaluate effects of preharvest applications of plant resistance inducers 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 test development of postharvest diseases during cold storage. After cold storage for four weeks, there were no significant differences in incidence of fruit rots resulting from natural infections between potassium silicate- or benzothiadiazole-treated fruit and the water control. Determination of fruit quality parameters is still in progress. The effects of potassium silicate on fruit rots in 2022 differed from those observed in 2021, where potassium silicate significantly reduced incidence of fruit rots resulting from natural infections by 46% compared to the water control. Additional research is needed to verify the effects of potassium silicate on postharvest fruit rots of blueberries.
In support of Sub-objective 2A, research continued 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 concentrations of natamycin were used for both application methods. Two non-treated controls (water applied by a conventional sprayer and an electrostatic sprayer) were also included. The experiment was conducted on two blueberry varieties Jewel and San Joaquin. Fruit were stored at 0 C for four weeks, at which time decay development was evaluated. Natamycin at both rates was equally effective and significantly reduced fruit rots resulting from natural infections regardless of application methods compared to the water control. On Jewel, natamycin reduced the incidence of fruit rots from 19.1% to 0.4-0.8% by conventional spraying and from 15.6% to 1.2-2.3% by electrostatic spraying in comparison with the non-treated control. On San Joaquin, natamycin reduced the incidence of fruit rots from 22.7% to 0.5-2.4% by conventional spraying and from 15.5% to 0.5% by electrostatic spraying in comparison with the non-treated control. 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 further support of Sub-objective 2A, an experiment was conducted to evaluate effectiveness of natamycin as a postharvest fogging treatment for control of 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 C. Blueberries were placed in plastic totes and 65 totes with five totes at each layer were palletized. The pallet was placed and covered with tarp to make a tunnel, and an 18-inch high velocity fan was placed at the end of the tunnel while the other end remained open, allowing fogged droplets to travel through the pallet. Five gallons of natamycin solution were fogged for 40 minutes, followed by 20 minutes of waiting time for fogged droplets to settle down, whereas the control treatment was fogged with water. Fruit were then packed into six ounce clamshells and stored at 0-1 C for four weeks. In the control, 31.7% of fruit were decayed while 25.9% of fruit were decayed in the fruit fogged with natamycin. In our previous study, natamycin was demonstrated to be highly effective to control postharvest fruit rots of blueberries when fruit were treated by spraying or dipping with natamycin. Although natamycin as a fog treatment significantly reduced fruit rots compared with the nontreated control, the effectiveness of natamycin was lower than when natamycin was applied as a dipping or spray treatment in our previous studies. This may be due to the poor coverage of natamycin solution during fogging, suggesting that the application method employed in this study needs to be improved.
In support of Sub-objective 2B, blueberries from two varieties were coated with 1% chitosan, 1% Semperfresh, or 2% sodium caseinate or carnauba immediately after harvest and stored for various times and temperatures designed to simulate initial storage, transportation, and marketing. None of the coatings were effective in reducing weight loss or slowing quality loss as estimated by other quality parameters. The only exception to this was a reduction in decay due to chitosan application, although a failure to reduce water loss limited the positive impact of this coating. Also problematic was the change in appearance caused by the coatings due to a loss in surface bloom. Experimentation indicated, however, that loss of surface bloom was not responsible for the poor performance of the coatings.
In further support of Sub-objective 2B, experimentation was conducted to determine the importance of the blueberry surface bloom to consumer acceptance, a question that had not been investigated previously. Blueberries were presented to sensory panelists with varying degrees of bloom removal, and it was found that panelists could tolerate a small amount of bloom removal but disliked fruit with major bloom removal. This work has implications to both the usage of coatings or other aqueous treatments and on the amount of handling-induced bloom removal that is permissible.
Also in support of Sub-objective 2B, reduction in the percentage of vent in plastic clamshells was tested for a second season as a means of reducing water loss in blueberries after harvest. Reducing the vent area in six ounce clamshells from 4.8% (commercial vent area) to less than 1% dramatically reduced weight loss in storage and greatly decreased the amount of shrivel observed after a period of simulated storage, transport, and marketing. Firmness tended to be higher in fruit from low vent clamshells while decay was unchanged. Reduction in clamshell vent size provides benefits throughout the entire marketing chain and may be feasible in operations that cool the blueberries prior to packing.
In support of Sub-objective 2C, ‘Early Muscat’ grapes were stored in either air, 1% oxygen, or 1% oxygen + 10% carbon dioxide for three weeks in cold storage to find a means to preserve muscat flavor after harvest. The muscat flavor characteristic present in some table grapes is prized by many but quickly fades in storage. Storage in either controlled atmosphere composition resulted in a preservation of muscat flavor, while grapes stored in air lost almost all muscat flavor. The resulting flavor corresponded closely to the content of linalool, an important muscat volatile, present in the grapes. Further work is ongoing to better characterize muscat flavor response to controlled atmospheres.
In further support of Sub-objective 2C, experiments were conducted on two table grape varieties Scarlet Royal and Autumn King to evaluate the effectiveness of natamycin (a biofungicide) for control of postharvest diseases. Natamycin was applied to commercially harvested grape clusters as either a dip or spray treatment whereas water was used as a non-treated control. Four rates of natamycin tested were full, 1/2, 1/4 and 1/8 recommended label rates. Fruit evaluations were conducted after cold storage for 26 days and subsequently, 2 additional days at room temperature. On Scarlet Royal, the dip treatment significantly reduced fruit rots resulting from natural infections from 18.2% in the non-treated control to 0.5-2.8% in the natamycin-treated fruit, and the spray treatment significantly reduced fruit rots from 18.7% in the nontreated control to 0.7-3.9% in the natamycin-treated fruit. On Autumn King, the dip treatment significantly reduced fruit rots resulting from natural infections from 11.3% in the non-treated control to 0.1-1.7% in the natamycin-treated fruit, and the spray treatment significantly reduced fruit rots from 11.4% in the non-treated control to 0.3-1.6% in the natamycin-treated fruit. Also, natamycin treatments did not negatively affect the appearance of rachis of grape clusters and there were no significant differences in the fruit firmness for both varieties. In separate experiments, fruit inoculation tests were conducted on both varieties to determine the effect of different concentrations of natamycin on the control of gray mold caused by Botrytis cinerea. Natamycin at full, 1/2, 1/4 and 1/8 recommended label rates significantly reduced disease incidence and severity on table grapes inoculated with Botrytis isolates regardless of application method and incubation temperature. In general, the 1/2 and full label rates were consistently more effective than 1/4 and 1/8 rates. These results suggested that no lower than 1/4 rate of natamycin may be needed to control gray mold on table grape berries.
Accomplishments
1. Determining the importance of blueberry surface bloom to consumers. A prominent feature of blueberries is the powdery coating (bloom) present on the fruit surface, yet there have been no formal sensory studies to determine its actual importance to consumers. ARS researchers at Parlier, California, in collaboration with the University of California, conducted sensory evaluation of blueberries with different degrees of bloom removal and determined that small but not major losses are acceptable to consumers. This research is useful to manufacturers developing blueberry coatings that can damage the bloom and for understanding how much care is warranted in trying to limit loss of bloom during picking and postharvest handling.
2. Postharvest use of peroxyacetic acid 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 are 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, tested peroxyacetic acid (PAA) as a postharvest dip or spray treatment for control of postharvest fruit rots of blueberries. PAA significantly reduced fruit rots and in general did not adversely affect fruit quality and sensory quality of blueberries. PAA is considered a generally-recognized-as-safe substance. The results showed that PAA is a promising postharvest tool to reduce postharvest fruit rots and maintain fruit quality of fresh blueberries.
Review Publications
Wang, F., Saito, S., Michaillides, T.J., Xiao, C. 2021. Baseline sensitivity of Alternaria alternata and A. arborescens to natamycin and control of alternaria rot on stored mandarin fruit. Plant Disease. 105(11):3653-3656. https://doi.org/10.1094/PDIS-04-21-0809-RE.
Saito, S., Wang, F., Xiao, C. 2022. Natamycin as a postharvest treatment to control gray mold on stored blueberry fruit caused by multi-fungicide resistant Botrytis cinerea. Postharvest Biology and Technology. 187. Article 111862. https://doi.org/10.1016/j.postharvbio.2022.111862.
Saito, S., Wang, F., Obenland, D.M., Xiao, C. 2021. Effects of peroxyacetic acid on postharvest diseases and quality of blueberries. Plant Disease. 105(10):3231-3237. https://doi.org/10.1094/PDIS-10-20-2310-RE.
Wang, F., Seiya, S., Michailides, T.J., Xiao, C. 2021. Phylogenetic, morphological, and pathogenic characterization of Alternaria species associated with fruit rot of mandarin in California. Plant Disease. 105(9):2606-2617. https://doi.org/10.1094/PDIS-10-20-2145-RE.
Wang, F., Saito, S., Michailides, T., Xiao, C. 2022. Fungicide resistance in Alternaria alternata from blueberry in California and its impact on control of Alternaria rot. Plant Disease. 106(5):1446-1453. https://doi.org/10.1094/PDIS-09-21-1971-RE.
Hausch, B.J., Arpaia, M., Campisi-Pinto, S., Obenland, D.M. 2021. Sensory characterization of two California-grown avocados (Persea americana Mill.) over the harvest season by descriptive analysis and consumer tests. Journal of Food Science. 86(9):4134-4147. https://doi.org/10.1111/1750-3841.15867.
Afifi, M., Obenland, D.M., El-kereamy, A. 2021. The complexity of modulating anthocyanin biosynthesis pathway by deficit irrigation in table grapes. Frontiers in Plant Science. 12. Article 713277. https://doi.org/10.3389/fpls.2021.713277.
Alzohairy, S., Gillet, J., Saito, S., Naegele, R.P., Xiao, C., Miles, T. 2021. Fungicide resistance profiles of Botrytis cinerea isolates from Michigan vineyards and development of a TaqMan assay for detection of fenhexamid resistance. Plant Disease. 105(2):285-294. https://doi.org/10.1094/PDIS-05-20-1087-RE.
