Effect of Chilling and Day Length on Runner of Everbearing Type Strawberry

Recently our research center developed two everbearing strawberry cultivars, 'Natsuakari' and 'Dekoruju'. Everbearing strawberry plants often produce few runners and a shortage of daughter plants could prevent rapid diffusion of these cultivars. We investigated some environmental factors that could have an effect on runnering. Fresh plants were rooted in pots during summer and kept outdoors. After they received respectively 0, 700, 1000, 1500 and 2000h of chilling (<5°C), plants were transferred into a greenhouse where the temperature was set at minimum 15°C. Half the plants from each chilling treatment were exposed to natural day length and the remainder exposed to a 16h day length. Both cultivars with 1000h chilling under 16h day length produced runners, but under natural day length they did not. The 1500 and 2000h chilling treated plants produced runners regardless of day length. Potted plants kept in a greenhouse to avoid chilling were transferred into a low temperature incubator set at -1.5°C. After 0, 30, 60, 90, 120 and 150 days, they were returned to a greenhouse and put under 16h day length regime. 'Dekoruju' plants receiving 30 days of chilling exposure produced runners while 'Natsuakari' needed at least 60 days to form runners. For both cultivars, plants that received 90 days of chilling produced most runners. Potted plants overwintered outdoors were grown under 10, 12h and natural day length beginning in May. Cv. 'Natsuakari' plants, exposure to longer day length produced more runners. For 'Dekoruju' exposure to natural day length resulted in fewer runners than exposure to 10 or 12h day length, perhaps as a result of increased flowering under long day conditions. In conclusion, both cultivars produced runners after receiving more than 1000h chilling outdoors provided sufficient hours in the daily light period. It was also shown that a refrigerator can be used to impose chill treatments when the natural environment is not conducive.