Effects of air and soil temperatures on the chemical composition of fruit and agronomic performance in strawberry (Fragaria x ananassa Duch.)

The effects of different air and soil temperatures on the levels of bioactive components in strawberry fruit (cv. Elsanta) were studied under Winter greenhouse conditions, as were agronomic parameters such as fruit yield, fruit size, and leaf area. The following three temperature Treatments were applied: A, cool (day/night: 16 degrees C/12 degrees C); B, warm (day/night: 22 degrees C/16 degrees C); and C, warm with soil heating to 26 degrees C during the day. Increasing the air temperature in the greenhouse, or the soil temperature, decreased the average fruit weight. Fruit quality attributes such as dry matter and soluble solids contents, and titratable acidity, were not significantly influenced by the different treatments. Strawberries grown in the cool environment (Treatment A) had a lower anti-oxidant capacity, in terms of their total phenolics (TP) content, trolox equivalent anti-oxidant capacity (TEAC), and oxygen radical absorbance capacity (ORAC), than strawberries produced in the warmer environment (Treatment B). This was due to lower concentrations of total monomeric anthocyanins, total pro-anthocyanidins, total ellagitannins, and kaempferol 3-glucoside-malonate. On the other hand, ascorbic acid concentrations in fruit grown in the cooler environment were higher compared to fruit grown in the warmer environment. An increase in soil temperature in the warmer environment (Treatment C) did not result in any additional accumulation of anthocyanins, or any other phenolics in the fruit, except for p-coumaroyl glucose. However, the concentrations of pro-anthocyanidins were even lower in fruit grown with heated soil. These results showed that air and soil temperatures have a significant influence on the phenolics composition of strawberries.