PCD Perera1, Nilanthi Dahanayake1*, SGJN Senanayake 1 and SA Krishnarajah2
1Department of Agricultural Biology, Faculty of Agriculture, University of Ruhuna, Mapalana, Kamburupitiya, Sri Lanka
2Royal Botanical Gardens, Peradeniya, Sri Lanka
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 effective 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 mgL-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 tetraploid plants were acclimatized and transferred to field to observe the morphological
characters. Factorial Complete Randomized Design (FCRD) with 10 replicates was used for each
treatment and statistical analysis was carried out using Duncan’s Multiple Range Test of
SAS program (9.1.3). The highest percentage of tetraploid plantlets (26.6%) was observed
from nodal cuttings treated with MS basal medium with 2mgL-1 BAP + 30mgL-1 colchicine 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.
Key words: colchicine, chromosome, diploid, Exacum ritigalensis, tetraploid
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