Korean native Veronica rotunda and Veronica longifolia are day-neutral plants with no vernalization requirements

Veronica rotunda var. subintegra (Nakai) T. Yamaz. (mountain spike speedwell) and V. longifolia L. (long-leaf spike speedwell) are Korean native plants that have potential value as novel ornamental crops due to their unique appearance and flowering time. This study was conducted to examine the effects of cold and photoperiod treatments on the growth and flowering of two Veronica species. Eight-week-old seedlings with four or five nodes grown under a 9-h photoperiod were stored at 5 °C for 0, 3, 6, 9, or 12 weeks and then forced under one of six photoperiod conditions [9, 12, 14, 16, or 24 h of continuous light or 9 h with a 4-h night interruption (NI, 22:00 to 02:00 HR)] in a greenhouse. Regardless of cold treatment, there were no significant differences among photoperiod treatments in any growth parameter (i.e., plant height, numbers of nodes or branches, leaf length or width, shoot or root dry weight) in either species. In plants without cold treatment, V. rotunda var. subintegra showed more than 85.7% flowering regardless of photoperiod, and flowering of V. longifolia was 80.0, 66.7, 70.0, 85.7, 71.4, or 100.0% under photoperiods of 9, 12, 14, 16, or 24 h or NI, respectively. The number of nodes below the first inflorescence, the number of visible inflorescences (VI) at the first open flower, and days to VI were not influenced by photoperiod in either species. As a result, cold treatment was not necessarily required for the flowering of the two Veronica species. Moreover, photoperiod also did not affect the flowering of either species. These results indicate that the two Korean native Veronica species can be classified as day-neutral plants with no vernalization requirement.