Date of Award

8-2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Committee Member

Guido Schnabel, Committee Chair

Committee Member

Juan Carlos Melgar

Committee Member

Sarah White

Abstract

Streaks lacking pigmentation in the skin of red blush cultivars of peaches have impacted many East Coast production areas. The underlying cause of streaking is unclear. Some evidence suggests that streaking may be caused by reactive agents in rainwater. Peach skin streaking was monitored over two consecutive years at a commercial farm with a history of streaking located near Ridge Spring, South Carolina. Six cultivars (two early season, two mid-season, and two late season cultivars) were evaluated each in two locations (LocA and LocB). Among those 12 experimental block cultivars, streaking occurred only in 2017 in cv. Scarletprince of LocA with an incidence of 6%. That same year two nearby non-experimental blocks with cv. Scarletprince revealed 11% and 25% streaking. Streaking was also monitored at the Musser Fruit Research Center (MFRC) in Seneca, SC. At that location, a high incidence of streaking was observed with 50% and 64% in cvs. Julyprince (2017) and Carored (2018), respectively. Rainwater pH taken from each of the 12 experimental blocks ranged from 3.03 to 7.4, ozone (O3) levels ranged from <0.02 to 0.37 mg/l, and chlorine (Cl2) and chlorine dioxide (ClO2) levels were either just above or under the detection limit of 0.01 mg/l and 0.02 mg/l, respectively. Although the electrical conductivity (EC) was below 100 μS/cm on average, we measured EC values as high as 1500 μS/cm. For all samples, the oxidation-reduction potential (ORP) ranged from 90 to 302 mV, indicating oxidizing conditions. Fruit harvested one or two weeks prior to commercial maturity and treated with solutions of high (10) or low (3) pH, ozone >0.37 mg/l and EC values of up to 3000 μS/cm did not produce symptoms. However, streaking was reproduced with collected rainwater, but the remaining sample volume did not allow further analyses. Using 0.05% ClO2 to induce streaking, we show that fruit of different cultivars varied in susceptibility when treated one week prior to commercial maturity with cv. Juneflame being the most susceptible and cv. August Lady being the least susceptible. Our study shows that multiple factors determine the occurrence of streaking in peach orchards, including cultivar susceptibility, ripening stage, and the presence of rainwater with sufficient amounts of a yet unknown reactive agent or agent combination.

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