Meiotic chromosome behavior of pollen mother cells and pollen variation in triploid hybrid between section Tacamahaca and sect. Aigeiros of Populus

ObjectiveRecently, techniques for induction of triploid hybrids between section Tacamahaca and sect. Aigeiros of Populus have been developed and a number of triploid germplasms were produced. However, reproductive developmental characteristics on these triploids are still in lack, which restrains their potential in sexual utilization. This study analyzed meiotic feature of pollen mother cells (PMCs) and pattern of gametic variation in a triploid hybrid, to lay a foundation for chromosomal engineering breeding of Populus using triploids as intermediate materials.

MethodIn this study, meiotic chromosomal behaviors of PMCs and pollen morphological variation between a male triploid hybrid WT-21, which derived from hybridization of induced 2n female gametes of P. pseudo-simonii × P. nigra ‘Zheyin3#’ and P. × beijingensis, and a male diploid hybrid WD-2 from the same combination were compared by the squashed technique with aceto-carmine.

Result(1) Whether for WT-21 or for WD-2, we observed the kinds of meiotic chromosomal behaviors, such as precocious chromosome migration, lagging chromosomes and micronuclei, reflecting high heterogeneity between parental genomes. (2) Misorientation of spindles during the second meiotic division, including parallel spindles, fused spindles and tripolar spindles, were found both in WT-21 and WD-2 and premature cytokinesis was produced in WT-21, which resulted in formation of dyads and triads in meiotic products. (3) In WT-21, 44.55% pollen grains were shrunken, which was higher than that of WD-2. Compared with WD-2, diameter of spherical pollen grains in WT-21 was significantly bigger than that of WD-2. From pollen diameter distribution, we could presume that the WT-21 could produce a small number of unreduced pollen grains. Pollen germination test showed that the germination rate of WT-21 was (1.08 ± 0.44)%, which was significantly lower than that of the WD-2 (28.67% ± 2.04%).

ConclusionAffected by both ploidy effect and heterozygosity, there are complex meiotic chromosomal behaviors during PMC meiosis in triploid hybrids, which would influence gametic development. Pollination with pollen of triploids would produce aneuploid and tetraploid offspings, laying the foundation for chromosome manipulation of Populus.