Native ornamentals for water- wise landscaping

Abstract

The investigation entitled “Native ornamentals for water-wise landscaping” was conducted in the Department of Floriculture and Landscaping, College of Agriculture, Vellanikkara, with an objective to conduct the morphological evaluation of native ornamentals and to assess the suitability of selected native ornamentals for water wise landscaping. The study was conducted as two experiments i.e., morphological evaluation of native ornamental species and evaluation of native ornamental plants for drought stress tolerance. The native species selected for the first study were Murraya paniculata, Barleria mysorensis, Rauwolfia tetraphylla, Barleria strigosa, Clerodendrum inermi, Carmona retusa, Melastoma malabathricum, Ecbolium viride, Eranthemum capensis and Pogostemon quadrifolius. Significant variations were observed for vegetative and flower characters and air pollution tolerance index among the ten native species. Maximum plant height was observed in Murraya paniculata (65.00 cm), which was on par with Clerodendrum inermi (60.87cm). Plant spread was also maximum in Murraya paniculata (41.33 cm). The number of primary branches was the highest in Clerodendrum inermi (6.43), which was on par with Pogostemon quadrifolius (6.15). Clerodendrum inermi also recorded the highest number of secondary branches (11.33), which was on par with Eranthemum capensis (10.33). The highest number of leaves was observed in Clerodendrum inermi (95.33). The leaf length recorded the highest value in Ecbolium viride (9.01 cm), which was on par with Barleria strigosa (8.00 cm). The leaf breadth was recorded highest in Barleria strigosa (7.33 cm) followed by Eranthemum capensis (4.33 cm). The qualitative vegetative characters like leaf type (simple/ compound), shape of leaf lamina, type of leaf base, margin and tip, leaf surface texture (coarse or fine), pubescence (present or absent) and leaf colour (as per RHS colour chart) were also exhibited wide variability. Among the floral characters, the maximum flower diameter was recorded in Melastoma malabathricum (4.83 cm), maximum length of the flower stalk in Barleria strigosa (3.67 cm), maximum number of flowers in Barleria mysorensis (50.00), flowering duration in Melastoma malabathricum (7.33 months) and field life of flowers in Barleria strigosa (3.67 days). Qualitative characters of flowers like flower type (solitary / inflorescence), colour of flower (as per RHS colour chart), fragrance (presence/absence), season of flowering and field life of flowers (days) also recorded wide variation. Based on their APTI value Carmona retusa can thus be included under the moderate tolerant group and Pogostemon quadrifolius under the sensitive group. Melastoma malabathricum can be used as edge, hedge and flower borders. Murraya paniculata having the highest plant height and plant spread can be used as hedge. Barleria strigosa can be used for hedge planting. Clerodendrum inermi which recorded the highest number of leaves and plant height can be used as hedge and for topiary. In the second experiment the native ornamentals were evaluated for their drought stress tolerance. Morphological characters like plant height, shoot and root biomass, stem diameter, leaf fresh and dry weight and stem diameter decreased in drought condition when compared to control. Total root length and root-shoot ratio increased under drought condition compared to control. Physiological parameters like RWC and membrane stability reduced under 5-day and 10-day water stress. Biochemical parameters photosynthetic pigments and starch decreased under 5 day and 10-day stress. Anatomical characters like higher stomatal index and lowest cell size were observed in plants subjected to 10-day stress. Clerodendrum inermi recorded the highest root length (92 cm) under 10-day stress. Clerodendrum inermi recorded highest relative water content (86.98 %) under control. Rauwolfia tetraphylla recorded the highest root-shoot ratio (0.97), carotenoid (0.10 mg/g), proline (96.44 μmol g-1FW) and MDA (1.63 μmol g-1FW) under 10-day water stress. Barleria mysorensis showed the highest membrane stability index (100.46) and lowest MDA (0.14 μmol g-1FW) under control. Thus Rauwolfia tetraphylla, Clerodendrum inermi, Murraya paniculata, Melastoma malabathricum and Barleria mysorensis can be suitably used for water-wise landscaping