Yuka Nakano

Delay of flowering by high temperature in chrysanthemum: heat-sensitive time-of-day and heat effects on CsFTL3 and CsAFT gene expression

Summary High temperature-induced delay of flowering is a major problem during the production of short-day (SD) plants such as Chrysanthemum.We have investigated the heat-sensitive hours for flowering in C. seticuspe. Heat treatment at 30°C was applied for 16, 8, or 4 h d-1, at different times of the day, under SD conditions (8 h photoperiod from 08.00 - 16.00 h), using 20°C as the optimum temperature. Heating between midnight and dawn (00.00 - 08.00 h) delayed floral initiation for up to 2 d, but delayed flowering for > 25 d, which represented the heat-sensitive hours for capitulum development. Heating during this period suppressed expression of the FLOWERING LOCUS T-like3 (CsFTL3) gene, a promoter of flowering induced in leaves by SDs. However, expression of CsFTL3 was higher compared to non-floralinductive photoperiods with a night-break. The anti-florigenic FT/TFL1 family protein gene (CsAFT) is an inhibitor of flowering induced in leaves by long-days. Expression of CsAFT remained low during heating under SDs, even when the plants flowered late. Our results show that high temperatures had little effect on floral initiation, which required suppression of CsAFT and a slight induction of CsFTL3 gene expression under SDs. In contrast, a high temperature between 00.00 - 08.00 h appeared to delay flowering by decreasing the level of expression of CsFTL3 required for capitulum development.

Differences in vernalisation responses in onion cultivars

ABSTRACT Onions normally form bulbs in the first year of growth; however, exposure to low temperatures can induce flowering (vernalisation) before bulbs are produced. Based on the cultivation data of onions grown in Japan, we evaluated and validated a reported model describing the onion vernalisation response. The observed bolting rates of ‘Sapporoki’, which was used in the construction of a previous model, were a good fit to the model, whereas, the bolting rates of one of the overwinter-type cultivars, ‘Momiji No.3ʹ, were lower than the predicted value. The difference between the predicted and observed bolting rates in ‘Momiji No.3ʹ was caused by a larger VD0.5, the coefficient in vernalisation response models that represents the time point when half of the plants have bolted. Overwinter-type and/or bolting resistant cultivars can have parameters that indicate a further vernalisation requirement for bolting. The parameters in our model can be customised to the cultivar being investigated, and our study suggests the viability of modelling onion bolting by using air temperature.