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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-1Indole-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 μm2) were larger than those of the diploids (1.94*1.48μm2). 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.
Highlights
Polyploidy breeding holds immense prospect in developing desirable varieties in flowering plants
Root induction from colchicine treated shoots of E. ritigalensis According to the result shown in table 2, the mean number of root and root length was reduced with time when increasing the exposure of stem explants to high colchicine concentration
In contrast with the above results,when increasing the colchicine concentrations, reduction of rooting and root length was observed by Dahanayake and Yue-Sheng (2013) and Elrad and Meral (2010).Conspicuously, survival rate was reduced when increasing the concentration of colchicine and its exposure time
Summary
Polyploidy breeding holds immense prospect in developing desirable varieties in flowering plants. It occurs around the Indian Ocean Basin, Africa, Madagascar, Socotra, the Arabian Peninsula, Sri Lanka, India, the Himalayas, mainland Southeast Asia including southern China, Malaysia, and northern Australia (Yuan et al, 2005; Sumanasinghe et al, 2012). This is an annual erect herb 50 – 100 cm in height, producing hermaphrodite flowers from light blue to dark blue with contrasting bright yellow anthers and shiny green foliage. Exacum ritigalensis is a horticultural plant with attractive blue col-
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