Growth Models for Helianthus annuus L. and Zinnia elegans Jacq.1

Abstract

Abstract A second degree central composite rotatable experimental design with 5 environmental variables (root temperature, day and night temperature daylength, and light intensity) was used to estimate growth response surfaces for Helianthus annuus cv. Mammoth and Zinnia elegans cv. Eldorado grown in controlled environment chambers. Fresh and dry weight of shoots, dry weight of roots, and total dry weight for sunflowers produced estimated equations suitable for first approximation response surfaces. The model predicted maximum growth (weight) of sunflowers occurred outside of the design space. More experimentation is needed at root temperature >26.7°C, day/night temperature >37.8°, light intensity >37800 lux and daylength >23 hours to find those conditions that maximize growth with the 5 environmental variables in the present study. Additional experiments at the boundary of design space are suggested for substantial improvements in the present model for sunflowers. In zinnia lack of significance of the estimated equation was observed for all measured growth parameters (fresh and dry weight of shoots, dry weight of roots, total dry weight, number of leaves, stem length, and leaf area). A leaf disorder resembling calcium deficiency was noted on zinnia plants grown at a root temperature of 26.7°C.