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United States Department of Agriculture

Agricultural Research Service


Location: Commodity Protection and Quality

2009 Annual Report

1a.Objectives (from AD-416)
This project includes multidisciplinary work on maintaining the quality of California-grown fresh commodities. Research will be conducted on the effects of postharvest treatments on injury and decay, the relation between fruit phenology and susceptibility to decay, and the effects of postharvest treatments on the composition of fresh commodities. This research seeks to:.
1)Minimize postharvest decay losses of citrus and grapes using microbial biological control, generally-recognized-as-safe (GRAS) or reduced-risk compounds, and thermal treatments. .
2)Identify and quantify morphological features (e.g. pericarp thickness, porosity, cell density) and constitutive or inducible biochemical constituents (e.g. phytoalexins, PR proteins, phenolic compounds) in grape selections that could mediate resistance to Uncinula necator and Botrytis cinerea. .
3)Determine the relationship of antioxidants with peel quality in lemons and fruit volatile content, brix and acidity on consumer acceptance of navel oranges as influenced by maturity and postharvest handling.

1b.Approach (from AD-416)
Evaluate the effectiveness of microbial biological control antagonists, substances classified as GRAS, certified organic, or reduced-risk compounds and thermal treatments in controlling significant postharvest pathogens of citrus fruit and grapes using laboratory assays. Promising treatments will then be included in large scale semi-commercial tests with cooperators to optimize their efficacy and assess their commercial feasibility. Assess resistance to gray mold (Botrytis cinerea) and powdery mildew (Uncinula necator) among grape selections using laboratory and field evaluations. Constitutive or inducible biochemical constituents and morphological features from these selections will be quantified to determine their contribution to disease resistance. Subject lemons to various durations and degrees of heat treatments and assay areas of the peel that show incipient injury for antioxidant status as well as for signs of oxidative injury. Measure fruit volatiles and quality factors such as brix and acidity and relate to the palatability of the fruit as influenced by time of harvest and various postharvest handling treatments. Formerly 5302-43000-029-00D (8/04).

3.Progress Report
A large consumer panel test was conducted in the Chicago area to evaluate the ability of a proposed new measurement standard, known as BrimA, to determine the initial time when navel oranges can be legally harvested in California. BrimA was more closely linked to consumer satisfaction than the current standard, which was a poor predictor of acceptability. Late-season navel oranges were evaluated for both sensory characteristics and flavor volatile content in order to better understand why flavor can sometimes be poor in navel oranges harvested at this time during the season. Individual fruit differed greatly in flavor but these differences were not conclusively linked to differences in sugars, acids or flavor volatiles. Mandarin orange flavor was found to be strongly influenced by storage time and temperature, the effect being dependent on the mandarin variety. Postharvest decay annually causes significant losses of fresh citrus fruit and table grapes. A brief postharvest treatment with heated potassium phosphite effectively controled postharvest decay alone, improve the activity of fungicides, and to partially control fungicide-resistant strains of the pathogen, while pre-harvest applications of potassium phosphite were found not promising, since they injured trees when used at concentrations that controlled postharvest decay. Preharvest applications of ‘reduced-risk’ fungicides reduced subsequent decay (mostly caused by Botrytis cinerea) significantly, and supplemental potassium fertilization, applied directly into clusters, markedly improved the firmness, color, and sugar content of ‘Redglobe’ grapes, with some reduction in postharvest decay.

1. Evaluation of a New Method for Maturity Determination in California Navel Oranges. The current maturity standard that determines when navel oranges can be harvested in California sometimes allows fruit with poor flavor to enter the market. Two large consumer panels were conducted in the Chicago area by an ARS researcher from the San Joaquin Valley Agricultural Sciences Center, along with university and industry collaborators, these panels verified that BrimA, an alternative measurement to estimate navel orange maturity, is superior to the current standard as a predictor of consumer acceptability. Adoption of BrimA as a new maturity standard by the California citrus industry would help ensure that only navel oranges with good flavor reach consumers and aid in increasing the profitability and competitiveness of the navel orange industry.

2. Minimizing Fungicide Use on Fresh Citrus Fruit After Harvest. Fresh citrus decay rapidly during storage unless actions, usually the application of fungicides, are taken to control the fungal decay pathogens that cause this problem. In work conducted by ARS scientists at the San Joaquin Valley Agricultural Sciences Center, brief postharvest treatment with heated potassium phosphite was shown to effectively control postharvest decay alone, improve the activity of fungicides, and to partially control fungicide-resistant strains of the pathogen. This practice is a useful option for citrus packinghouse managers to increase the shelf and storage life of fresh citrus fruit. This work clarifies the benefits and risks of using this material, and shows it has considerable promise as a treatment to control decay losses in the fresh citrus industry, an industry that produced 90 million boxes worth approximately $1,000,000,000 in California alone in 2008.

3. Preharvest Applications to Grapevines to Control Postharvest Decay of Table Grapes. Postharvest quality is an important aspect of marketing table grapes, but the influence on postharvest quality of preharvest fungicidal applications is poorly known. ARS scientists at the San Joaquin Valley Agricultural Sciences Center in Parlier in 2008 and 2009, applied several of the best performing ‘reduced-risk’ fungicides and found they reduced the postharvest incidence of decayed berries by nearly 90% in the most effective and intensive spray program, in most tests with commercial vineyards and sprayers. The postharvest decay was reduced about 50%. The study elucidates methods and timing of ‘reduced-risk’ fungicide applications so as to minimize costly postharvest decay losses for table grape growers. This work provides information about the selection and scheduling of ‘reduced-risk’ fungicide treatments that are an important element in the control of decay losses in the $1.2 billion California table grape industry.

Review Publications
Montesinos-Herrero, C., Smilanick, J.L., Hurley, J.M., Lluis, P. 2009. Potassium sorbate residue levels and persistence in citrus fruit as detected by a simple colorimetric method. Journal of Agricultural Food & Chemistry. 57(9):3458-3463.

Palou, L., Smilanick, J.L., Crisosto, C. 2009. Evaluation of food additives as alternative or complementary chemicals to conventional fungicides for the control of major postharvest diseases of stone fruit for the control of major postharvest diseases of stone fruit. Journal of Food Protection. 72(5):1037-1046.

Obenland, D.M., Margosan, D.A., Collin, S., Sievert, J., Fjeld, K., Arpaia, M., Thompson, J., Slaughter, D. 2009. Peel fluorescence as a means to identify freeze-damaged oranges. HortTechnology. 19:379-384.

Obenland, D.M., Collin, S., Mackey, B.E., Sievert, J., Field, K., Arpaia, M. 2009. Determinants of flavor acceptability during the maturation of navel oranges. Postharvest Biology and Technology. 55(2):2009:156-163.

Obenland, D.M., Collin, S., Sievert, J., Field, K., Toyota, M., Doctor, J., Arpaia, M. 2008. Commercial Packing and Storage of Navel Oranges Alters Aroma Volatiles and Reduces Flavor Quality. Postharvest Biology and Technology. 47(2):159-167.

Last Modified: 7/24/2014
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