Confirmation of everbearing mutants in the everbearing strawberry cultivar ‘Natsuakari’ and the effect of an overwintering condition on inflorescence and runner development

The everbearing strawberry cultivar ‘Natsuakari’ produces high-quality fruits and can be harvested in summer and autumn. However, flowering-defective individuals have been recently found at some farms in the Tohoku region. To solve this problem, we first investigated the behavior of flowering-defective individuals collected from three places in Aomori, Akita, and Miyagi prefectures and confirmed that the non-flowering phenomenon reproducibly occurred during summer and autumn. Next, we analyzed the genotypes of flowering-defective individuals using highly polymorphic simple sequence repeat (SSR) markers suitable for cultivar discrimination and SSR markers linked to the everbearing gene. As a result, flowering-defective individuals showed the same genotype as the original ‘Natsuakari’, and the fragment linked to the everbearing gene was not detected in flowering-defective individuals. It was suggested that cultivar contamination was not the cause of the non-flowering phenomenon, and that mutations may be present in flowering-defective individuals. To confirm the effects of previous history before transplanting on the flowering and runner development of normal flowering plants and the flowering-defective mutants, the influence of potting time of the daughter plant and overwintering conditions were investigated. The potting time had no effect on flowering or runner development. Inflorescences in the normal flowering plants continuously emerged, especially in summer and autumn under both heated and non-heated conditions during overwintering. The mutants hardly flowered in the summer and autumn under both conditions, although the inflorescences emerged in the early summer under the heated condition during overwintering. The number of runners observed in the mutants was higher than that in the normal plants throughout the study, especially in the summer, while in both heating during overwintering led to much less runner development in May through July. According to these results, although the mutants were suitable for plant propagation, defective flowering persisted in subsequent years. Therefore, to ensure stable production, it is important to observe flowering types in mother plants with adequate chilling and to select mother plants exhibiting flowering in summer and autumn.