A Comparative Study of Various Methods of Root-tip Preparation in Screening Wheat Aneuploids1

The increasing use of aneuploid stocks in wheat cytogenetic studies has created a need for efficient means of determining the chromosome numbers of large plant populations. Furthermore, an increasing number of synthesized species from crosses between wheat and its relatives is being developed. In order to maintain those synthetics, a rather extensive selection of euploids against aneuploids is required, because of their irregular meiosis. Improvements of the Feulgen squash method by Hillary (1939, 1940), Darlington and La Cour (1947) and others allowed a root-tip count for an efficient way of determining the chromosome number. Kihara (1927) noted first that cold treatment arrested meiosis at metaphase. The same effect of cold on mitosis was reported by Barber and Callen (1943) in animals and by Baily (1954) and Brauer (1950) in plants. Owing to their findings, the ap plication of cold became a well established pretreatment in chromosome analysis. The root-tip count of chromosomes after cold treatment and Feulgen squash method is now in general use for screening wheat aneuploids. How ever, there are no detailed informations published on the subject. In order to fill the increased requirements for a mass-handling of aneuploids, the authors have attempted to establish the most efficient and economic way of screening with respect to time, space and labor. An experiment was designed so that effects of different cold treatments on mitosis could be studied in regard to the number of cells in division, the length of metaphase chromosomes and their spreading. Cytological data ac cumulated from a series of aneuploid screenings now allow a comparison of root-tips collected at different stages of plant growth.