Interpretation of growth regulator research with floriculture crops. [Conference paper].

This paper discusses many factors affecting results of growth regulator research, and illustrates the need for their consideration in interpreting research results, especially when comparing experiments. It also emphasizes the need for the best possible control of all factors so one may make valid comparisons. The discussion also shows why, in commercial glasshouse crop production, growth regulator practices which presumably are made in conformity with recommendations based on research may not produce exactly the same results as expected or predicted. As an example, consider the information on growth and flowering of Clerodendrum thomsoniae Balf as reported by Hildrum (1973, 1974) and by Koranski et al. (1976 1978, 1979). One sees the complicated interrelationships and effects. The following are some of the factors: 1. Variation in degree of flowering of clonal selections, some "positive" and some "negative". 2. Light intensity - whether in growth chambers or natural light. In chambers, fewer flowers under low light intensity (under 1200 foot-candles) than with high (6500 ft-c). 3. Effect of exact length of the photoperiod. 4. Light quality - differences between incandescent and fluorescent light for extending the photoperiod. 5. Root medium - plants grown in soil mix, peat-lite mix or peat alone may react differently. 6. Soil moisture - greater amounts of retardant required for plants grown with capillary mat watering. 7. Defoliation and water stress - defoliated and water-stressed plants produced axillary shoots at 79 per cent of the nodes compared to 5 per cent for plants not defoliated or water-stressed. 8. Source of cuttings - cuttings from uppermost portion of young plants (4 months) developed 5 times as many flowers as cuttings from old stock plants (1-1/2 years). 9. Distinction between effect of retardation on flower bud initiation, development, and actual flowering time.