ASHS 2025 Conference

Production of mandarin, sweet orange, and grapefruit has increased in most tropical and subtropical areas of the world in recent years due to growing market demand for high-quality, blemish-free fruit. Citrus fruit grown in the coastal region of the southeastern U.S. are more susceptible to blemishes and poor peel color than those grown in cooler climates. Early season, Florida mandarins are commonly degreened by treating with ≤ 5 ppm of ethylene for 12 h to 72 h at 29 °C /96% relative humidity (RH). However, optimal citrus degreening conditions vary with citrus cultivar, growing area, stage of maturity and season. Additionally, degreening can negatively affect mandarin quality (flavor, nutrition, acidity, sensory acceptability) and promote postharvest decays. The objective of this study was to evaluate the postharvest quality of two seedless mandarin cultivars degreened at temperatures lower than the commercial standard of 29 °C. These cultivars were released by the University of Florida breeding program: ‘UFGlow’, grown on ‘Rich’ trifoliate, ‘Carrizo’ citrange or ‘Sun Chu Sha’ mandarin rootstocks, and ‘UFSunrise’, grown on ‘Rich trifoliate’, ‘Carrizo citrange’ or HRS 812 rootstocks and were compared to the commercial cultivar ‘Owari-satsuma’, grown on ‘Carrizo citrange’ rootstock. On the day of harvest, fruit of each cultivar were pooled, treated with 5.0 μL·L-1 ethylene in a humidified, flow-through system for 72 hr at 20, 25 or 29 °C and 95% RH, then transferred to 8 °C/87% RH and evaluated weekly for 21 days. The three cultivars had better peel color and higher peel total carotenoid content when degreened at 25 or 29 °C than at 20 °C. Soluble solids content and total titratable acidity changed slightly during storage, independent of degreening treatment. Degreening did not affect ascorbic acid content; fruit total antioxidant capacity (oxygen radical absorbance capacity, ORAC) declined less with the ethylene treatment but remained constant in ‘UFGlow’. The best degreening treatment for these seedless mandarin cultivars was 5 ppm ethylene at 25 °C/96% RH for 72 hr, resulting in the best peel color, highest total peel carotenoids content, less weight loss and firmer fruit. Although ‘Owari’-satsuma developed better color at 29 °C, weight loss was significantly higher than when degreened at 20 or 25 °C.