Phenotypic Plasticity Index as a Tool to Assess the Suitability of Three Coleus (Plectranthusscutellarioides (L.) R.Br.) Varieties in Low- Maintenance Landscaping

Abstract

People often demand low-maintenance landscape designs. Ability of plants to survive and adapt to different ecological breadths while maintaining the aesthetic appeal is associated with the low- maintenance. Selecting plants for low-maintenance landscape designs is a difficult task. Without a proper objective tool to support decision making, selection is often made based on prior experience or trial-and-error basis, which involves a greater degree of subjectivity. Phenotypic Plasticity Index (PPI) is a relatively new tool to support in selecting plants to be grown under an environmental gradient continuum. In this study, PPI of 10 morphological and physiological traits of three varieties of Plectranthusscutellarioides (L.) R.Br. (Coleus), grown under a light gradient continuum, were calculated using minimum and maximum least square means of the trait. They were also grouped into three categories as high, moderate and low phenotypic plasticity, based on calculated PPI values. The highest plasticity was shown by the parameters related to photosynthesis such as chlorophyll and anthocyanin concentrations while the number of branches, plant height and number of leaves remained in moderate plastic category implying that the species did not try to alter its morphology drastically. These plasticity indexes indicate that all three varieties rely much on shade tolerance over shade avoidance. Furthermore, low plasticity of parameters which explains the plant architecture (height, branching, number of leaves) expresses that the effect of shade is minimum to the aesthetic qualities of three varieties of Coleus suggesting them as potential candidates for low- maintenance landscaping.