Induction Of Chromosome Doubling Of Embryo Sac In Populus Tomentosa By High Temperature Exposure

P. tomentosa clones 3119,3532 and 8212 with higher seed setting rate from many years of field observations were selected as female parents, and P. alba x P. glandulosa clone YX1 as male parent. Culturing the branches nearby pollination can overcome embryo abortion derived from malnutrition of the branches. In this study, these clones were used as female parents to develop triploid-induction techniques of high-temperature induced embryo sac chromosome doubling in P. tomentosa. Some advances were made as follows.(1)Triploid P. tomentosa germplasms originated from female gamete chromosome doubling were obtained firstly by treating female catkins with high temperature after pollination. A total of 458 triploid hybrids of P. tomentosax(P.alba×P. glandulosa) were produced, with an average induction rate at 62.06%. These triploids included, in detail,221 plants from female parent clone 3119 with 57.97% induction rate,230 plants from female parent clone 3532 with 65.71% induction rate and 17 plants from female parent clone 8212 with 70.83% induction rate. No triploid was detected in control groups. Considering the temperature and duration of treatment,it was suitable for embryo sac chromosome doubling of P. tomentosa with 39 or 42℃ and the duration of 2 or 4h in 4-52h after pollination.(2) It was proven that the cytological mechanism of triploid induction through treating pollinated female catkins with high temperature was embryo sac chromosome doubling. After embryological observation of one of the female parents, P. tomentosa clone 3119, it was showed that its embryo sac developed during 4-64h after pollination, undergoing uni-nucleate stage, two-nucleate stage, four-nucleate stage, eight-nucleate stage and mature embryo sac. It indicated that the high-temperature treatments were located within the three rounds of mitosis. However, there was asynchronous development among different catkins, even different ovules within same ovary.(3)Compared with diploid offspring, these P. tomentosa triploid hybrids had advantages in growth and photosynthetic characteristics. Based on analysis of the three combinations, it was found that both height and basal diameter of triploid seedlings were highly significantly larger than that of the diploids. Although there was no significant difference between triploid and diploid seedlings, the net photosynthetic rate and transpiration rate of the triploid seedlings were larger than that of the diploids. The diurnal variations of the net photosynthetic rate and transpiration rate in the triploid seedlings were consistent with that of the diploids. Moreover, stomatal conductance of the triploids was significantly higher than that of the diploids.