Location: Commodity Protection and Quality Research
2016 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
In research under Objective 1A, mandarins harvested late in the season were found to be more susceptible to off-flavor formation during storage than fruit harvested in the early part of the season. This difference was associated with the late-harvested fruit having lower internal oxygen levels and a higher concentration of ethanol in the juice following waxing and storage. A mandarin variety that was highly susceptible to loss of flavor quality in storage was found to develop poor flavor due to a severe depletion in internal oxygen concentration following waxing.
Alternaria alternata and A. arborescens are two major fungal species responsible for Alternaria rot of blueberries grown in the Central Valley of California. In research under Objective 1B, sensitivity or resistance of Alternaria isolates to fungicides was tested. In A. alternata, 59% and 73% of the isolates were resistant to the fungicides fludioxonil and cyprodinil, respectively, and 41% of the isolates were resistant to both fungicides. In A. arborescens, 47% of the isolates were resistant to both boscalid and pyraclostrobin, 8% of the isolates were resistant to fluopyram, and 33% of the isolates were sensitive to all three fungicides.
In research under Objective 1B, on the blueberry fruit that were treated with fungicides before harvest, prothioconazole (Proline) and the mixture of cyprodinil and fludioxonil (Switch) reduced the incidence of Alternaria rot on inoculated fruit by 80% and 55% compared to the nontreated control, respectively. Fenhexamid (Elevate) did not control Alternaria rot. Fenhexamid and cyprodinil+fludioxonil reduced the incidence of gray mold on inoculated fruit by 67% and 27% compared to the nontreated control, respectively. Prothioconazole did not control gray mold.
Postharvest fumigation of blueberry fruit with ozone at concentrations ranging from 0 to 1000 ppm was evaluated in research under Objective 1B. All ozone treatments reduced the incidence of Alternaria rot and the spread of the fungus Botrytis cinerea among the fruit compared to the nontreated control. Ozone concentrations of 300, 500, and 1000 ppm provided better control of both diseases than concentrations <300 ppm.
In research under Objective 1C, the mixture of the fungicides fluopyram+pyrimethanil (Luna Tranquility), fluopyram+tebuconazole (Luna Experience), fenhexamid (Elevate), and cyprodinil+fludioxonil (Switch) applied before harvest reduced the number of infected grape berries resulting from fruit-to-fruit spread by mycelium of Botrytis cinerea. Switch and Luna Tranquility were the best treatments to prevent gray mold during storage. On wounded fruit, Elevate effectively reduced the incidence of gray mold, followed by Switch. All fungicide treatments significantly reduced the lesion size of gray mold on the grape fruit compared to the control. Overall, Elevate and Switch appeared to be the best treatments.
Effects of ozone fumigation on fungicide residues on blueberry fruit were evaluated in research under Objective 2A. Organic blueberry fruit were treated in the lab with fungicides fenhexamid, fludioxonil and cyprodinil mixture, azoxystrobin, pyrimethanil, or captan and subjected to ozone fumigation at 2000 ppm or 5000 ppm for two hours. Ozone fumigation did not cause visible phytotoxicity on the fruit compared to the nonfumigated control. Fungicide residues on treated fruit are currently being analyzed.
Accomplishments
1. Harvest date influences postharvest off-flavor development in mandarins. Mandarins often develop an off-flavor in storage that harms marketability, but adequate means to consistently prevent it have not been developed. ARS researchers in Parlier, California harvested mandarins at various time points from early to late season and determined the sensory properties of the fruit following waxing and storage. It was found that early-season fruit were less susceptible to off-flavor than fruit harvested late in the season. The finding provides a potential way to lessen flavor quality loss in mandarins during storage and may help enable a further understanding of how off-flavor occurs. This can act to enhance profitability to the citrus industry as a whole by increasing the likelihood of repeat consumer purchases by better preventing poor-tasting mandarins from being in the marketplace.
2. Mucor rot, an emerging postharvest disease of mandarin citrus fruit. In recent years, an emerging, undescribed postharvest disease was observed on mandarin fruit after extended storage in California. ARS researchers in Parlier, California, conducted surveys for postharvest diseases affecting mandarins and found that this undescribed disease is common on stored mandarins, that five Mucor species are responsible for Mucor rot on mandarins, and that M. piriformis was the most predominant and virulent species. If it is left uncontrolled, Mucor rot can cause significant economic losses of mandarin citrus fruit worth $500 million annually. The determination of the cause of this emerging disease is the first step towards the development of effective control measures.
None.
Review Publications
Pokorny, A., Smilanick, J.L., Xiao, C., Farrar, J.J., Shrestha, A. 2016. Determination of fungicide resistance in Botrytis cinerea from strawberry in the Central Coast Region of California. Plant Health Progress. 17:30-34. doi: 10.1094/PHP-RS-15-0053.
Saito, S., Michailides, T.J., Xiao, C. 2016. Mucor rot - An emerging postharvest disease of mandarin fruit caused by Mucor piriformis and other Mucor spp. in California. Plant Disease. 100:1054-1063. doi: 10.1094/PDIS-10-15-1173-RE.
Saito, S., Margosan, D.A., Michailides, T.J., Xiao, C. 2016. Botrytis californica, a new cryptic species in the B. cinerea species complex causing gray mold in blueberries and table grapes. Mycologia. 108:330-343. doi: 10.3852/15-165.
Kim, Y.K., Kwak, J.H., Aguilar, C.G., Xiao, C. 2016. First report of black rot on apple fruit caused by Diplodia seriata in Washington State. Plant Disease. 100:1499. doi: 10.1094/PDIS-12-15-1463-PDN.
Obenland, D.M., Cantwell, M., Lobo, R., Collin, S., Sievert, J., Arpaia, M. 2016. Impact of storage conditions and variety on quality attributes and aroma volatiles of pitahaya (Hylocereus spp.). Scientia Horticulturae. 199:15-22.
Zhu, X.Q., Xiao, C. 2015. Phylogenetic, morphological and pathogenic characterization of Alternaria species associated with fruit rots of blueberry in California. Phytopathology. 105:1555-1567. doi: 10.1094/PHYTO-05-15-0122-R.
Kim, Y.K., Saito, S., Xiao, C.L. 2015. Occurrence of fludioxonil resistance in penicillium digitatum from citrus in California. Plant Disease. 99:1447.
Wiseman, M.S., Kim, Y.K., Dugan, F.M., Rogers, J.D., Xiao, C. 2016. A new postharvest fruit rot in apple and pear caused by Phacidium lacerum. Plant Disease. 100:32-39. doi: 10.1094/PDIS-02-15-0158-RE.
