GROWTH AND FLOWERING OF GYPSOPHILA-PANICULATA L BRISTOL FAIRY AND BRIDAL VEIL IN RELATION TO TEMPERATURE AND PHOTOSYNTHETIC PHOTON FLUX

The growth and flowering responses Of Gypsophila paniculata L. 'Bristol Fairy' and 'Bridal Veil' to temperature and photosynthetic photon flux (PPF) were determined by growing plants in controlled environment rooms under all the following combinations of PPF (210, 450 and 710 mumol s-1 m-2) and temperature (12, 20 and 28-degrees-C). 'Bristol Fairy' showed higher relative growth rate and root: plant ratio, but lower leaf area ratio than 'Bridal Veil' over the first 30 days of treatments. Temperature and PPF responses of net photosynthesis were similar in the two cultivars and were characterized by a temperature optimum which shifted from 20-degrees-C at 450 mumol s-1 m-2 to between 12 and 20-degrees-C at 710 mumol s-1 m-2 Stem elongation (bolting) commenced first at 28-degrees-C and 710 mumol s-1 m-2 and was delayed progressively at 20-degrees-C and 12-degrees-C, and at lower PPF. Plant height at harvest was inversely related to temperature, but increased with increasing PPF. Generally, bolting and flower bud formation occurred earlier in 'Bridal Veil' than in 'Bristol Fairy'; flower buds developed to anthesis more rapidly in 'Bridal Veil' at 12-degrees-C, but not at 20-degrees-C or 28-degrees-C. Flower yield was inversely related to temperature and was higher in 'Bridal Veil' than in 'Bristol Fairy' under all except 28-degrees-C growth conditions. Flower yield decreased with PPF in both cultivars, but 'Bristol Fairy' displayed more blindness and flower bud abortion at 210 mumol s-1 m-2. The ratio of floret number to inflorescence fresh weight (a measure of inflorescence density) was generally higher in 'Bridal Veil' than in 'Bristol Fairy'. 'Bridal Veil' shows considerable promise for commercial production, particularly under lower temperature and PPF conditions.