Flowering of Heliconia angusta

Abstract

The minimum daylength requirement for flower bud initiation in R. angusta was 13 hr for 7 weeks. Anatomical analysis of shoot apex also confirmed transformation of vegetative apex to reproductive apex under daylengths 13 hr or longer. In daylengths longer than 13 hr, the differences in daylength had no significant effect on flowering time which was 16 weeks after long-day treatment. Longer duration of treatment produced more flowers. The number of shoots per pot had negative relationship with number of flowers showing mutual shading effects of leaves and pseudostems. Length of flower stalk had a positive correlation with the number of bracts. The effect of environmental factors on flower development was investigated. Daylengths of 12, 14, 16, 18 hr had no effect on time to flower after initiation or number of flowers, but plants grown in 18 hr produced longer flower stalks. Night temperature had a significant effect on the number of flowers, or flower quality. Differences in light intensity during flower development had no effect on flowering time, but flower numbers per pot and length of flower stalk were increased with an increase in light intensity. Leaf elongation pattern was analyzed using growing degree day (GDD) units. An S-curve equation (y=a/ (l+e^(-b-k*x))) better described the leaf elongation patterns than linear and negative exponential curves. The GOD unit requirement based on daily average temperature with a base temperature at 14°C from shoot emergence to leaf 3 and 4 expansion was 677-745 (42-54 days) and 930-992 (66-72 days) respectively. The average of elongation rates in leaves 1 to 5 was 25.4 mm/GDD and 3.8 cm/day. A model based on Honolulu daylength conditions including civil twilight showed that potential flower bud initiation under daylengths 13 hr or longer would be March 28-July 30, flower development would be May 16-December 5, and flowering time would be August 30-January 7. Validation with monthly harvest data from a commercial grower showed that 99.6% of flowers were harvested within the predicted flowering period. Based on Honolulu daylength and accumulation of GDD units calculated from weather data (from January 1, 1962 to December 31, 1991), the late possible shoot emergence dates for stems with fully expanded leaf 3 to initiate flower bud under daylengths of 13 hr or longer would be June 16-28.