Induction of Polyploids in lemon (Citrus limon (L.) Burim. f.) by Colchicine Treatment

Abstract

Studies on the effects of colchicine on seed germination, seedling development and chromosome doubling in lemon (Citrus limon (L.) Burm. f.) to attempt variety improvement by chromosome doubling.  The experiment  was carried out at the greenhouse of the Plant Science Department, Faculty of Natural Resources, Prince of Songkla University, hat Yai campus from june 2005 to January 2007.  Colchicine application was divided into 2 separated experiments.  The first one was seed application: Lemon seeds without their seed coats were soaked in clochicine solution with diffeent concentrations at 0 , 0.5, 1.0 , 1.5 and 2.0% for 36 hours and the treated seeds were then germinated.  The results showed that germination percentage, seedling height, length and width of leaves and number of leaves per plant of the control treatment were very high, compared to all colchicine-treated plants.  The LD50 of colchicine concentration for seed application from this study was 1.88%.  However, all colchicine-treated concentrations failed to incuce chromosome doubling in lemonseedlings.  The another experiment was shoot tip application.  The active growing shoot tips of 8-nibtg-old seedlings were coated with cotton wool soaked with different concentrations of colchicines solution at 0, 0.5, 1.0, 1.5 and 2.0% for 24 hours.  Twenty - five shoot tips were used for each concentration and data were recorded as previously described in the first experiment.  It was found that growing shoot tips as percentage and their length, leaf width/length and number of leaves were all highest in the control treatment.  The LD50 of colchicine concentration for shoot tip was 0.94%.  For the chromosome count, only 1 individual plant from each of the 1.0 and 2.0% colchicine-treated concentrations showed chromosome changing, however, both wee mixoploid.  The ploidy levels of the 1.0% colchicine- triploid (2n=3x=27) and tetraploid (2n=4x=36), while only diploid and tetraploid cells were observed in the 2.0% colchicines- treated plant.