Growth relationships of individual flowers during late stages of floral development of Rhododendron L-'Prize' and 'Gloria'

Single terminal inflorescences from two-stemmed plants of Rhodadendron L, c v. 'Prize' and 'Gloria' were recurrently sampled during a 9 degrees C cold treatment and subsequent forcing period in an 18 degrees C growth chamber u ntil plants reached anthesis. At each sample period, bud length and width w ere measured on each inflorescence, while subtending bud scale, petal, stam en ('Gloria' only), style, peduncle and ovary length, ovary width, and flow er weight were determined on the tao most basally attached flowers within a n inflorescence for each cultivar. Polynomial regression models were calcul ated for each floral growth measurement over time, except for bud length an d width, for each of the four flowers within a cultivar. Comparison of regr ession models revealed differences in floral part growth patterns among the various flowers within each cultivar. During the first week of placement i n 18 degrees C forcing temperatures after the cold treatment, bud length wa s the only floral part to grow on 'Prize' plants, while only female flower parts grew on 'Gloria' plants. These results indicate differences in growth resumption patterns between cultivars after cold storage. However, petal a nd style length were strongly correlated to flower weight for both cultivar s indicating that these measurements could be used in laboratory or field s ituations to determine the floral stage of growth. The growth equations des cribed would be useful for controlling the variability among shoots and flo wers for analytical determinations, such as hormonal content analysis, and for studying relationships of floral growth patterns to environmental stimu li that could be used to control flowering. The statistical techniques used in this research make it possible to reduce the number of plants for such studies, as measurements taken on different flowers on the same plant can b e used for floral part growth comparisons despite the inherent correlation present between such measurements.