Role of environmental factors and plant growth regulators on the floral transition of Exacum Styer group
Creators: name: Krishnasamy, Rani
Publisher: name: University of British Columbia
Year: 2011

description: Exacum Styer Group exhibit many outstanding characteristics that make this crop suitable as a new flowering pot, bedding or cut flower crop. One requirement for a new crop's commercial success is a reliable system to predict or control flower initiation and development. Therefore, this study focuses on evaluating the role of environmental factors on the transition from vegetative to reproductive growth. Light treatments, based on a combination of shade nets and supplemental lights were designed to deliver between 1152 moles and 5211 moles of light over a 36 week period. Visual inspection of plants occurred daily with the dates of first visible bud and anthesis recorded from each individual within all populations (i.e., genetically related seedlings). Average number of days to visible bud and average number of days to anthesis for individual populations ranged from 170-218, and 237-280, respectively. Average number of days to anthesis for individual treatments were as follows: Treatment 1 (ambient light + 65% shade) 272 days; Treatment 2 (ambient light + 35% shade) 278 days; Treatment 3 (ambient light) 273 days; Treatment 4 (ambient light + supplemental light) 238 days. Analysis of variance results indicate significant effects (P&lt;0.05) on days to visible bud and days to anthesis for population, treatment, and their interaction. These sources of variation are partly attributed to the high level of heterozygosity within these populations reflective of their interspecific background. Changes in meristem structure associated with floral initiation were characterized across populations of Exacum Styer Group. Meristem anatomy and morphology were characterized from tissue harvested weekly and were based on light (i.e., anatomy) and scanning electron (i.e., morphology) microscopy. Structural changes associated with floral initiation were consistent across all individuals and populations and were successfully sub-divided into six relatively distinct stages. In Stage 1, the shoot apical meristem (SAM) is dome to conical shaped with a height to width ratio of 0.90 and without visible structures. In Stage 2, the apical dome becomes flattened as development progresses with the height to width ratio changing to 0.43 and remaining without visible structures. In Stage 3, five sepal primordia are initiated around the apex that resembles foliage leaves in both position and development. During Stage 4, the apex continues to flatten and broaden with a height to width ratio further reducing to 0.09, and with five petal primordia arising simultaneously alternate to the sepals. In Stage 5, initiation of the stamens occurs with their first appearance as short structures alternate to the petals. Finally, in Stage 6, the ovary is initiated. These observations on meristem transition are consistent with previous reports for many other angiosperm species and support these six stages of transition as fundamental in angiosperm development. Meristem width and height were used in allometric analyses and associated with environmental treatments (i.e., light unit sum, heat unit accumulation, time). Coefficients of determination obtained from simple allometric regression ranged from 0.468 (Population 02-65) to 0.980 (Population 02-62). To include additional sources of variation over that of the simple allometric regression (i.e., interactions between both the environment (i.e., treatments) and genotype (i.e., both within and among individual families)), an expanded power function model was developed. The best subset regression procedure was performed with the expanded allometric model to determine which independent variables were most appropriate to include in the multiple regression model. The models that displayed a low Mallow's Cp value, a low variance inflation value and a high R2 were selected as the most useful. Direct comparisons between the two allometric models were based on the magnitude of the partial regression coefficients for each parameter in the best subset models. Using the best subset regression results, significant standard partial regression coefficients were observed for light sum (11 of 13 populations) and days (7 of 13 populations) indicating these two parameters significantly affected floral initiation.