Sugar Concentration in Strawberry is Influenced by Temperature During Fruit Development

Abstract

Day neutral strawberries ( Fragaria × ananassaDuch.) produce fruit over several months, even in climates with cold winters. Air temperatures during these long fruiting periods can range from near freezing to close to 40 ˚C. We divided fruit development into four developmental stages and divided the typical air temperature range during the growing season into four non-overlapping intervals from 7 to 32 ˚C. We sampled fruit from a day neutral strawberry planting approximately once a week from July to Nov., calculated the number of hours that individual fruits were exposed to a particular temperature interval during each of the four developmental stages, then correlated this number with the soluble solids concentration (SSC) of the harvested fruit. We found that warm air temperature exposure (16 - 23 ˚C) early in fruit development was positively correlated with final SSC at harvest, but SSC increased further when fruits were exposed to cooler air temperatures (7 - 15 ˚C) for the 15 days prior to harvest. Exposure to air temperatures above 24 ˚C at any developmental stage resulted in fruit with lower SSC. Our data provide field validation that strawberry sweetness is highest under moderately cool temperatures, and sugar concentration is reduced when developing fruits are exposed to hot (>24 ˚C) temperatures as fruit approach ripening. It may be possible for growers to minimize the amount of time air temperatures exceed 24 ˚C by using evaporative cooling, reflective low tunnel coverings or shade cloth to enhance the sugar concentration of fruit.