Microsporogenesis in the triploid hybrid 'Beilinxiongzhu 1#' and detection of primary trisomy in 2x x 3 x Populus hybrids

Primary trisomy is a powerful genetic tool in plants. However, trisomy has not been detected in Populus as a model system for tree and woody perennial plant biology. In the present study, a backcross between Populus alba x Populus glandulosa 'YXY 7#' (2n = 2x = 38) and the triploid hybrid 'Beilinxiongzhu 1#' (2n = 3x = 57) based on the observation of microsporogenesis and an evaluation of the variations in pollen was conducted to create primary trisomy. Many abnormalities, such as premature migration of chromosomes, lagging of chromosomes, chromosome bridges, asymmetric separation, micronuclei, and premature cytokinesis, have been detected during meiosis of the triploid hybrid clone 'Beilinxiongzhu 1#'. However, these abnormal behaviors did not result in completely aborted pollen. The pollen diameter of the triploid hybrid clone 'Beilinxiongzhu 1#' is bimodally distributed, which was similar to the chromosomal number of the backcross progeny. A total of 393 progeny were generated. We provide a protocol for determining the number of chromosomes in aneuploid progeny, and 19 distinct simple sequence repeat (SSR) primer pairs covering the entire Populus genome were developed. Primary trisomy 11 and trisomy 17 were detected in the 2x x 3 x hybrid using the SSR molecular markers and counting of somatic chromosomes. Nineteen distinct SSR primer pairs for determining chromosomal number in aneuploid individuals were developed, and two Populus trisomies were detected from 2x x 3 x hybrids by SSR markers and somatic chromosome counting. Our findings provide a powerful genetic tool to reveal the function of genes in Populus.