Study on aneuploidy in tetraploid sugar beet populations and their triploid progenies

In tetraploid plants due to formation of quadrivalent, trivalent, bivalent and univalent at metaphase I, meiosis goes unbalanced, so at the end of meiosis division there will be gametes which their number of chromosomes are more or less than normal. Upon fusion of these gametes with each other or with gametes of a diploid male sterile plant, aneuploid progenies will be obtained. This phenomenon may affect yield and sugar content. In this investigation, aneuploidy frequency in tetraploid populations and their triploid progenies was studied. Three tetraploid populations named 10026-55, 10980-56 and 11479-57 which were second, third and forth generation of process of tetraploid lines production from diploid lines by using Colchicine and their triploid progenies namely 10035-55, 10986-56 and 11488-57 were used. Rootlets and seedlings of each tetraploid population and its triploid progeny were used for chromosome counting. Average aneuploidy frequency for three tetraploid populations at rootlet and seedling stages was 29 and 24 percent, while this amount for triploid progenies was 17 and 10 percent, respectively. Root yield, sugar content and some other parameters of aneuploid and euploid plants of each population were measured. Results indicated that aneuploidy caused 1 to 1.5 percent sugar content reduction and 4 to 5 percent root yield reduction. In order to determine the selection effect on the reduction of aneuploidy in tetraploid populations, some euploid plants with 36 chromosomes were selected from each population. After vernalization, selected roots of each population were transferred to isolated plots for seed production. A part of collected seeds were planted to produce roots. When rootlets appeared, their chromosomes were counted. Therefore, the frequency of aneuploidy in newly obtained seeds was determined. Based on the results, selection of plants having 36 chromosomes and seed harvesting from them had no affect on the reduction of aneuploidy.