Growth and anatomical responses in Xanthostemon chrysanthus as influenced by Paclobutrazol and Potassium Nitrate

Abstract

A study was conducted to determine the effects of a plant growth regulator (paclobutrazol, PBZ) and commercial fertilizer (Krista-K Plus) as a source of potassium nitrate (KNO3 ) on the growth of Xanthostemon chrysantus. It was also attempted to investigate the anatomical changes in the leaf and stem after the treatment. Nine treatments, i.e. control (no PBZ and Krista-K Plus application), 0 PBZ gL-1 + 100 g Krista-K Plus, 0 PBZ gL-1 + 200 g Krista-K Plus, 0.125 PBZ gL-1 + 0 g Krista-K Plus, 0.125 PBZ gL-1 + 100 g Krista-K Plus, 0.125 PBZ gL-1 + 200 g Krista-K Plus, 0.25 PBZ gL-1 + 0 g Krista-K Plus, 0.25 PBZ gL-1 + 100 g Krista-K Plus and 0.25 PBZ gL-1 + 200 g Krista-K Plus, were tested. PBZ was soil drenched at the commencement of the study while Krista-K Plus was applied at three-month intervals. Plant growth performances such as tree height, diameter at breast height, canopy diameter and leaf area were recorded monthly throughout the study period. Stem and leaf samples were collected before the application of treatments and after six months of treatments for anatomical observation by using electron microscope. Plant height, diameter at breast height, crown diameter and leaf area were significantly reduced with the application of PBZ. Palisade parenchyma thickness was increased by 33.83% with 0.25 PBZ gL-1 + 200 g Krista-K Plus, while only 2.44% increment recorded in the control tree. Xylem thickness in the stem was reduced by 21.81% after treated with the highest dosage of PBZ, while the control tree only had 1.78% increment. Spongy parenchyma thickness in the leaf was unaffected. However, palisade parenchyma was found the thickest after combined treatment with 0.25 PBZ gL-1 + 200 g Krista-K Plus. Micrograph images of the cross-section of leaf lamina and stem showed that the cells were tightly arranged in response to the application of PBZ.