Effects of root zone heating during daytime at different growth stages on the flowering, growth and yield of strawberry [Fragaria ananassa] 'Akihime' grown in substrate culture

The effect of daytime root zone heating at different stages on the flowering, growth and yield of strawberry (Fragaria x ananassa Duchesne, 'Akihime') was studied by growing the plants under substrate culture in a heated plastic house. Two experiments were conducted. Experiment 1 was performed from September 28, 2007 to April 30, 2008 and Experiment 2 was conducted from December 6, 2007 to April 30, 2008. Both experiments consisted of one control (non-heated) and three treatments. In Treatment 1 (T1), the substrate was heated for the whole growing period (from the flower bud initiation stage to the end of the experiment). In Treatment 2 (T2), heating was initiated at the flowering stage (from flowering time to the end of the experiment). In Treatment 3 (T3), heating was initiated during the flower bud development stages (from flower bud initiation stage to flowering stage). Results showed that root zone heating treatments during daytime at the terminal flower cluster hardly affected the flowering date of the terminal flower of each cluster and fruit yield. There was no significant difference in the development of flower buds by any heating treatments. However, root zone heating treatments during the daytime at the flowering stage of the second lateral flower cluster tended to enhance the date of flowering at the terminal flower of the 2sup(nd) lateral flower cluster at T1 and T3, and that of the 3sup(rd) lateral flower cluster at all heating treatments. Fruit yield in February and March, and during the whole period increased at T1 and T3. The development stages of flower bud 5 weeks after initiation of the heating was advanced and the size of flower buds after heating treatments was significantly greater than that of the control. In conclusion, the present experiment showed that daytime root zone heating in the development stages of flower bud cluster during low temperature seasons (after December) enhanced the development of flower buds and then flowering, and finally increased the yield.