IN VITRO INDUCTION OF TETRAPLOIDS FROM EXACUM RITIGALENSIS (GENTIANACEAE)

Abstract

Exacum ritigalensis (Gentianaceae) (Sinhalese: Binara or Ginihiriya) has a potential to develop as a potted plant by improving the size of the flowers and inflorescence. The aim of the study was to establish an efficient and effec tive system for the production of tetraploid plants through colchicine treatment. Single nodal cuttings (0.5 cm) from aseptic plantlets were established on Murashige and Skoog basal medium (MS) supplemented with 2 mgL 1BAP and different colchicine concentrations (0, 10, 20, 30, 40 and 50 mg-1 ). They were kept in different durations (0, 7, 14 21 and 28 days) and transferred into 10ml of MS basal medium containing 2 mgL-1 BAP. After one month, they were transferred to MS medium containing 2mgL-1 Indole-3-butyric acid (IBA) for rooting. Then root tips were collected from treated plants to observe chromosome number. Afterwards the selected diploid and tetra ploid plants were acclimatized and transferred to field to observe the morphological characters. Factorial Com plete Randomized Design (FCRD) with 10 replicates was used for each treatment and statistical analysis was car ried out using Duncan’s Multiple Range Test of SAS program (9.1.3).The highest percentage of tetraploid plant lets (26.6%) was observed from nodal cuttings treated with MS basal medium with 2mgL -1 BAP + 30mgL -1 colchi cine for seven days. The chromosome number of diploid and tetraploid E. ritigalensis determined as 28 and 56 respectively. Cells of the tetraploid plants were comparatively larger cells than diploids plants. The stomata size of the tetraploid (2.96*2.27 μm 2 ) were larger than those of the diploids (1.94*1.48μm 2 ). Leaf shape of diploids was lanceolate while it was ovate or narrowly elliptic in tetraploids. Flower petals of diploid plants were overlapping along their entire length while in tetraploids flower petals were not overlapping. The plants height was significantly higher in diploid (67.00±9 cm) than in tetraploid (38.00±4 cm). Newly produced polyploids of E. ritigalensis have a potential to popularize as a potted plant in the floriculture trade.