Abstract
Effects of mist cooling during flower bud differentiation and the developmental phase on the flowering time and floret formation were investigated in summer-to-autumn flowering-standard type chrysanthemums, in order to avoid flowering delays caused by high temperatures in the Tohoku region. ‘Iwa-no-hakusen’, ‘Seikai’, and ‘Sei-no-nami’ were grown in a plastic greenhouse under a natural day length with or without long-day treatment about 40 days after cutting, and the mist was sprayed during flower bud differentiation and the developmental phase. Mist cooling reduced the air temperature of the plastic greenhouse and plants by about 3°C during spraying. Anthesis of ‘Iwa-no-hakusen’ was promoted by mist cooling without long-day treatment, and break budding was promoted by mist cooling with long-day treatment. Anthesis of ‘Seikai’ was promoted by mist cooling, and markedly affected compared to ‘Iwa-no-hakusen’. However, anthesis of ‘Sei-no-nami’ was not promoted by mist cooling. Mist cooling before flower budding tended to increase the number of involucral bracts in the capitulum of ‘Iwa-no-hakusen’ and decreased the number of florets in ‘Seikai’. In conclusion, in the Tohoku region, mist cooling can be used in ‘Iwa-no-hakusen’ if a marked effect is obtained during flower budding and break budding. In ‘Seikai’, mist cooling can be useful to regulate flowering, but it is not useful for ‘Sei-no-nami’.
