Preharvest Effects on Postharvest Quality of Strawberries Grown in High Tunnels

The incorporation of high tunnels for specialty crop production in the Great Plains region has dramatically increased. The utilization of high tunnels for spring-planted high tunnel strawberry production with day-neutral varieties could provide growers with both early and late-season income. However, it’s unclear if this system will produce adequate yields of high quality fruit during the extreme summer temperatures that are typical in the region. Our objectives were to identify day-neutral strawberry cultivars that succeed in a spring-planted, high tunnel system and investigate the treatment effect of evaporative cooling on the yield, quality, and shelf life of strawberries. The trial was conducted at the Kansas State University Olathe Horticulture Research and Extension Center during Summer 2014 and was planted in a three-season high tunnel with 30% shade cloth. The experimental split-plot, randomized complete-block design (RCBD) with four replications where the main plots consisted of the evaporative cooling treatment (with and without) and the sub-plots included the six commercially-available cultivars (Albion, Evie2, Monterey, Portola, San-Andreas, and Seascape). Evaporative cooling was applied twice daily for  five minutes when temperatures rose above 30 °C throughout July and August. Fully-ripened fruit were harvested twice per week and the marketable and total yield (lbs/plant) was monitored. After harvest, the strawberries were stored at 3 °C for 8 days. Shelf life was monitored daily with respiration rate, water loss, and decay by using a scale with scores from 1 (very poor) to 5 (excellent). Strawberry quality was evaluated by measuring color (CIE L*a*b*), total soluble solids, texture (firmness), and titratable acidity. Fruit nutritional quality on the day of harvest was evaluated by measuring total phenolic and total antioxidant content with hydrophilic and lipophilic oxygen radical absorbance capacity (ORAC) and ferric reducing ability of plasma (FRAP). The results indicate that throughout the entire season (10 May to 7 October), 'Portola' had the highest yield (1.32 lbs/plant), while 'San-Andreas' had the lowest yield (0.72 lbs/plant). Shelf life results illustrate that 'Seascape' and 'Evie2' decayed quicker with significantly more water loss in comparison to 'San-Andreas' and 'Portola' (P < 0.001). Similarly, texture measurements of 'Evie2' and 'Seascape' exhibit low firmness levels throughout the season (P < 0.001). Our results indicate that growing day-neutral strawberries in a high tunnel could be a successful system in the Great Plains when proper varieties are utilized. Further research is needed to investigate the utility of the cooling treatments across multiple growing seasons.