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Characterization of M1 Generation Of Polyploids in T. Pradeepkumar
Associate Professor, Department Of Olericulture, College Of Horticulture, Vellanikkara, P.O. Kau, TRICHUR,KERALA, Watermelon [Citrullus lanatus (Thunb.) Matsum and Results and Discussion Nakai] exhibit great variation in seed morphology, par- ticularly in seed size and shape, and in seed coat Seeds failed to germinate when exposed for 24 tissue texture, and color. However, in recent years, seed- hours to a concentration of 1, 1.5 and 2 % colchicine.
less watermelon are more acceptable to consumers, and Variable response to high concentration of colchicine seed companies make great efforts in breeding for high was reported by Jaskani (2005). Giant guard cell was quality seedless watermelon varieties. Kihara (1951) observed in plants generated through 0.1% colchicine produced triploid seedless hybrid watermelon by cross- seed treatment and 0.5% colchicine seedling treatment ing tetraploid (4n) and diploid (2n) plants. A large num- (Table 1). Polyploid plants had a higher chloroplast ber of triploid varieties have been developed in Asia and number, ranging from 17-22, while the diploid (control) North America. However, in contrast with the USA, seed- plants had about 12 chloroplasts in the stomata guard less watermelons have not been popular in India. There cells. Chloroplast counting is an efficient indicator of is a need to develop tetraploid breeding lines suitable polyploidy during early phase of plant growth (Jaskani for consumer needs in India. Breeding stable tetraploid et al., 2005) and a higher chloroplast number is an indi- line with adequate fertility is a major challenge in trip- cator for higher ploidy. In general, polyploids took more loid watermelon production (Mohr, 1986).
days to form male and female flowers (Table 2). Slower Compton et al. (1996) developed an easy technique for growth rate and delayed appearance of shoots and flow- the early identification of putative tetraploid watermelon ers were observed in colchicine treated seedlings. The plants. In tetraploid plants, the guard cells of the sto- same trend was also reflected in the days taken to har- mata contain a high number of chloroplasts compared with these in diploid plants. Here, a procedure has been Plants generated following treatment of seedlings optimized to induce polyploidy in the commercial wa- with 0.5 % colchicine produced large pollen grains (40.35 termelon cultivar Sugarbaby, and the resultant M1 gen- µ). Consequently, the polyploidy plants produced eration plants were morphologically characterized.
smaller fruits with a small number of seeds (Table 3).
The number of seeds produced in plants treated with 0.5 % colchicine (15-46 seeds) is significantly lower than that produced in the diploid control plants (430- Polyploidy was induced in the seeds and seed- 530 seeds). In general, plants regenerated from seeds lings of the watermelon variety Sugarbaby using colchi- treated with 0.1 % colchicine or from seedlings treated cine solution (0.1 % and 0.5%). The seeds of Sugarbaby with 0.5 % colchicine exhibited polyploidy characters.
were soaked in clean water for 6 hrs and then soaked for On the other hand, seedling treated with 0.1 % colchi- 24 hrs in a solution containing 0.1, 0.5, 1, 1.5, or 2.0% cine produced chimeral growth and normal fruits with colchicine. The seeds were briefly rinsed before sowing high seed numbers. Variability in colchicine tolerance in polybags filled with sand. For seedling treatment by watermelon lines was observed in a previous study seeds were sown in polyhouse. Once seedlings emerged, (Jaskani et al., 2004). The variable response of genotypes a drop of colchicine (0.1 or 0.5%) was applied to the to colchicine indicates that optimal colchicine concen- shoot apex between the cotyledons. The chemical solu- trations may vary in treating watermelon genotypes.
tion was applied to the growing point during morning Although tetraploid watermelon plants are mor- hours for three consecutive days. The plants derived phologically distinct, they may not be stable and pro- from seed and seedling treatments were examined with duce mixoploid vines on the same plant. Rose et al. (2000) respect size of stomata guard cells and number of chlo- reported that mixoploid plants in which more than 40% of the cells were tetraploid could be mistaken for full tetraploids but that mixoploids with 10–30% tetraploid 44 / Cucurbit Genetics Cooperative Report 33-34: 44-46 (2010-2011)
cells usually resembled diploid plants. However, chlo- roplast counts and other morphological features could Leaf Guard cell
be helpful in successive generations to develop pure line.
The results of this study underscore the need for con- tinual observation for distinguishing polyploids from diploid plants and presence of mixoploids calls for a cautious approach in breeding polyploid lines. Overall, ploidy level can be determined by examining epidermal tissue from the lower leaf surface, without the require- ments of specific equipment and high expenditure.
Compton, M.E, D.J. Gray, and G.M. Elmstrom. 1996. Identifica- tion of tetraploid regenerants from cotyledons of diploid watermelon cultures in vitro. Euphytica 87:165-172.
Jaskani, M.J., W.K. Sung, and H.K. Dae. 2005. Flow cytometry of DNA contents of colchicines treated watermelon as a ploidy screening method at m1 stage. Pakistan Journal of Botany Jaskani, M.J., S.W. Kwon, G.C. Koh, Y.B. Huh and B.R. Ko. 2004.
Induction and characterization of tetraploid watermelon.
Journal of Korean Society of Horticultural Science 45: 60- Kihara, H. 1951. Triploid Watermelons Proceedings of American Society of Horticulture Science 58 : 217-230.
Mohr, H.C. 1986. Breeding Vegetable Crops AVI Publishing Com- Rose, J.B., J. Kubba and K.R. Tobutt. 2000. Chromosome dou- bling in sterile Syringa vulgaris x S.pinnatifolia hybrids by in vitro culture of nodal explants. Plant Cell Tissue and Organ Table 1 : Leaf characters of plants produced
from seeds or seedlings treated with
colchicine versus untreated control plants.
(values are mean±SD , n=12)
Cucurbit Genetics Cooperative Report 33-34: 44-46 (2010-2011) / 45
Table 2 : Biometric characters of plants
produced from seeds or seedlings treated
with colchicine versus untreated control
Table 3: Fruit characters of plants produced
plants. (values are mean±SD , n=12)
from seeds or seedlings treated with
colchicine versus untreated control plants.
46 / Cucurbit Genetics Cooperative Report 33-34: 44-46 (2010-2011)

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