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G. Schnabel and C.H. Crisosto

Quinone outside inhibitor (QoI) fungicides can improve the yield and quality of cereal crops in the absence of disease pressure through the so called “greening effect,” but little is known about the potential beneficial effects on deciduous tree fruit crops. In a multiyear and multicultivar study carried out in South Carolina (2005 and 2006) and California (2006), we examined the potential influence of the QoI fungicide pyraclostrobin on antioxidant activity and commercially important peach (Prunus persica) fruit quality attributes, including fruit size, coloration, firmness, soluble solids concentration, and yield. Experimental orchards were sprayed according to commercial guidelines to manage insect pests and diseases. A pyraclostrobin + boscalid mixture was applied up to five times per season starting 1 week after the physiological stage of “shuck off” until 1 to 2 weeks before harvest. Fruit size was measured weekly between “shuck off” and harvest, whereas the other fruit quality attributes were determined at harvest. Results indicate no consistent impact of the pyraclostrobin + boscalid mixture on same-year fruit size development or other fruit quality attributes in orchards with no or very little disease pressure. To our knowledge, this is the first in-depth evaluation of the potential effects of a QoI fungicide on commercially important tree fruit quality attributes.

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C.H. Crisosto and M.A. Nagao

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Sanliang Gu, Carlos H. Crisosto, R. Scott Johnson, Robert C. Cochran, and David Garner

Fruit from 8 `Hayward' kiwifruit vineyards in central California were harvested at 2 week intervals after soluble solids content (SSC) reached 6% and subjected to 4 and 6 months of storage at 0°C in an ethylene free environment. Fruit characteristics at harvest and postharvest performance varied considerably among locations. Fruit stored for 6 months had the same fresh weight, less flesh firmness and higher SSC, than the 4 months storage. Later harvested fruit had greater fruit flesh firmness and higher SSC after storage. SSC after storage was predictable based on ripe soluble solids content (RSSC) at harvest. Summer pruning reduced while soil nitrogen application increased fruit SSC.

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C.H. Crisosto, W.A. Retzlaff, L.E. William, T.M. DeJong, and J.P. Zoffoli

We investigated the effects of three seasonal atmospheric ozone (0,) concentrations on fruit quality, internal breakdown, weight loss, cuticle structure, and ripening characteristics of plum fruit from 3-year-old `Casselman' trees in the 1991 season. Trees were exposed to 12-hour daily mean O3 concentrations of 0.034 [charcoal-filtered air (CFA)], 0.050 [ambient air (AA)], or 0.094 [ambient plus O3 (AA+O)] μl·liter-1 from bloom to leaf-fall (1 Apr. to31 Oct. 1991). Fruit quality and internal breakdown incidence measured at harvest and after 2, 4, and 6 weeks of storage at 0C were not affected by any of the O3 treatments. Following an ethylene (C2H4) preconditioning treatment, the rate of fruit softening, C2H4 production, and CO, evolution was higher for plums harvested from the AA + O than from those grown in CFA. Weight loss of fruit from the AA + O exceeded that of fruit from CFA and AA. Anatomical studies of mature plums indicated differences in wax deposition and cuticle thickness between fruit grown in AA + O, AA, and CFA. Differences in gas permeability, therefore, may explain the difference in the ripening pattern of `Casselman' plum fruit grown in high atmospheric O3 partial pressures.