Studies On Cucumber(Cucumis Sativus L)Ploidy Determination And Chromosome Doubling

System of cucumber haploid induction from unpollinated ovaries has been successfully established in Tianjin Cucumber Research Institute. The frequency of the regeneration has been over 20%. But the ploidy of plant population obtained are always a distribution of haploid, diploid, triploid, tetraploid and other ploidy levels. Ploidy determination was very important for the utilization of the plants. Haploid plants cannot be used in breeding and further genetic study until they were doubled.In present experiment, we have established a fast, reliable and precise method system for cucumber ploidy determination. Method for cucumber chromosome doubling was also studied. The main results were as follows:1. Study on Chromosome sample preparing in cucumberParameters and technique of chromosome preparing with wall degradation hypotonic method with tendril in cucumber were studied, and a suitable method was established. The results also indicated that there was a evident correlationship between chromocenter diameter, heterochromatin number and the plant ploidy level. The chromocenter diameter and heterochromatin number of haploid and double haploid are 5.1um, 5.2 and 13.3um, 10.7, respectively.2. Ploidy Determination in Cucumber(Cucwm/5 sativus L.)Various methods for ploidy determination based on somatic chromosome counting, chromocenter size, heterochromatin counting, leaf stomata size, guard cell chloroplast number and certain plant morphological characteristics, were investigated and evaluated in cucumber. The results indicated that chromosome counting was the most reliable and precise method, however, it was cumbersome and required skilled cytological techniques; The chromocenter size, heterochromatin number, chroloplast number of guard cell and certain plant morphological characteristics are simple and practical methods for ploidydetermination but with some shortages. Method based on nucleus DNA staining withDAPI was also tested and discussed.3. Study on Cucumber Chromosome DoublingStudy on cucumber chromosome doubling has also been carried out. The results indicated that soaking apical point with 0.2% colchicine for 7 hours was an efficient method for haploid doubling. However, the doubling frequency is relatively lower (6.3%) due to high temperature conditions in summer. Tetraploid induction from double haploid was also studied, and a desirable result has been obtained. Dripping the apical point of plantlets with 0.2% colchicine plus 1.5% DMSO was a suitable treatment with doubling frequency 18.2%. Smearing apical point with a mixture of 0.2% colchicine plus adeps lanae and 1.5% DMSO was also effective with doubling frequency 14.0%. Dripping the apical point of plantlets with trifluralin has also been tested, and it showed effective in inducing tretraploid from double haploid, but obviously delayed plant growth.