Polyploid Mutation And Level Determination Of Dendrobium Candidum

Polyploid mutation and level determination of Dendrobium candidum Wall, exlindl were systematically studied. Besides, a preliminary method for identifyingsuch polyploidy was established by comparing with the diploid. Results were asfollows:1, NAA was more effective than 2,4-D to increase the germination of D. candidium seeds in Ne medium. When its concentration was 0.5mg/L, germination reached to 83.17%.2, Study of the induced polyploidy of D. candidum in the process of tissue culture was made. Results indicated that polyploidy of D. candidum could be produced by immersing the protocorm-like bodies (PLBs) and the seedlings in colchicines solutions of different concentration, or by adding colchicines to the medium in tissue culture for a period of time before the culturing started. The former method was proved to be more useful in producing polyploidy. Seedlings immersed in 0.3% colchicines solution for 36h reached to the highest inducing ratio, 63.51%.3, The variant plants of D. candidum were distinguishable from the diploid morphlogically. They showed the following features: stems became dwarf and stout; leaves were thick and in dark green; plants grew up slowly.4, Before observing the chromosomes of D. candidum microscopically, its shoots were given pretreatment with 8-hydroxyl quinoline solution at 18℃ for 5h, digested in Imol/L HC1 at room temperature for 2h, then treated with improved carbol fuchsin. The chromosome number of tetraploid cells was 2n=4x = 76, while that of diploid cells was 2n=2x=38.5, The fact that induced plants had two groups of cells with nuclear DNA content different from each other, nearly 2:1 in ratio suggested that these inducing plantwere chimerals. The chromosome number was also in accord with this conclusion. In comparison with counting the chromosome number for identifying ploidy, another procedure for it using flow cytometry for identification of ploidy was simpler, rapid and accurate.6, The stomatal size of leaf lower epidermis of the polyploidy was larger than that of the diploid. The number of stomata per unit leaf area of the leaf in variant plants obviously reduced. The increase of the chloroplast number in guard cells was significant and it could be used as a reference for selecting polyploidy preliminarily from colchicines-treated plants prior to chromosome counting.7, No significant genetic differences in esterse isoezyme was observed between the diploid and ployploid. However, peroxidase isoezyme analysis showed that the enzyme activities between the polyploidy and the diploid plants were quite different. Two new bands were observed in the isoenzyme map of polyploidy plants and their Rf were 0.600 and 0.667 respectively.