The optimum conditions for inducing 2n pollen chromosome doubling by high temperature in Eucommia ulmoides

Based on the rule of meiosis of microspore, the effects of high temperature, duration and meiotic stages on percentage of 2n pollen were determined by a “living tree hightemperature doubler” using Eucommia ulmoides as the experimental material. The optimum conditions of 2n pollen induction were discussed. The experimental results indicated that significant correlations were found between meiotic stages and mean length, and mean diameter of male buds, and mean exposure length of anther. Thus these morphological indexes could be considered as a marker to the process of meiosis. The concept of weighted mean stage was taken into determination of meiotic stages in asynchronous studied material, which helped compare the quantified differences derived from different treatment combinations. Significant effects on induction percentage of 2n pollen from meiotic stages, high temperature and duration were observed when 2n pollen was induced by high temperature. To some extent, the optimum stage for pollen chromosome doubling by high temperature was a extensive process of meiotic stages. Exceeding 40% of 2n pollen could be obtained by high temperature treatment during diplotene, diakinesis, metaphse Ⅰ, anaphase Ⅰ and metaphse Ⅱ, respectively. Sensitivity to high temperature for male buds was relatively low in E. ulmoides. Therefore, a higher temperature and longer duration are needed when 2n pollen is induced by high temperature treatment.