JUDGMENT INDEX AND INHERITANCE OF CHILLING REQUIREMENT TO BREAK DORMANCY IN STRAWBERRY

Abstract

Strawberry cropping systems adapted to each district from the southern to northern parts of Japan were developed together with advancing of studies on ecotype characteristics of various cultivars and techniques of controlling flower induction and dormancy, resulting in many cropping systems. The cultivars adapted to forcing culture have shallow dormancy and those adapted to semi-forcing culture and open culture have deep dormancy. This experiment was carried out to determine a judgment index for the chilling requirement to break dormancy and to investigate the inheritance of dormancy in strawberry plants. Runner plants of 8 varieties with various chilling requirements to break dormancy were exposed to varying degrees of chilling under 5°C. Runnering was a more effective index than the sudden extension of petiole length. Moreover, the cessation of continuous flowering under the minimum temperature of 15°C with a 16h photoperiod was used to judge the chilling requirements to break dormancy because the coefficient of variation of runnering was smaller than that of the sudden extension of petiole length and the cessation of continuous flowering. Chilling requirements and the cumulative hours of chilling to break dormancy of the runner plants were longest, while that of the over-wintered seedlings was longer than that of the annual seedlings. Runner plants of the selfed seedlings and the crosses between seedlings of a shallow dormancy variety 'Nyoho' and deep dormancy varieties 'Aiko' and 'Pajaro' were used to investigated the inheritance of dormancy. The degrees of dormancy of the crossed seedlings were tend aside of parents with shallow dormancy. It seems that the selection of strawberry plants with deep dormancy needed the use of many seedlings.