Abstract
Interspecific hybrids often produce extensive gametic variation due to poor chromosome pairing and unbalanced chromosome segregation. To elucidate the influence of interspecific hybridisation on pollen variation in Populus L., we compared pollen size among three P. deltoides Marsh. clones, two P. nigra L. clones, and three P. deltoides × P. nigra hybrids and investigated the cytological mechanism of pollen variation by observing meiotic chromosome behaviour and microtubules. The frequency of shrunken and unstainable pollen grains was higher in the hybrids (15.54–57.28 %) than in the non-hybrid clones (0.98–4.82 %). The distribution of stained pollen size ranged more broadly in the hybrids than in the non-hybrids, suggesting that hybridisation increases pollen size variation. Precocious chromosome migration and lagging chromosomes were common in the hybrids, indicating poor chromosome pairing. Some micronuclei formed minispindles in metaphase II and emanated secondary nuclear-based radial microtubule systems in telophase II, undergoing cytokinesis to develop into microcytes in the meiotic products. Eliminated micronuclei might result in the formation of aneuploid pollen. The frequency of sporads with microcytes was higher in the hybrids (3.19–11.08 %) than in the non-hybrids (0–0.94 %). Disoriented spindles, including fused and tripolar spindles, led to the formation of dyads and triads, contributing to unreduced pollen production. These results provide new insights into the gametic variation of Populus interspecific hybrids and reveal several 2n pollen producers, which will be valuable in polyploid breeding of the section Aigeiros Duby.
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Acknowledgments
We thank the Forestry Research Institute of Tongliao City in the Inner Mongolia Autonomous Region, Yining Plain Forest Farm in Xinjiang and Beijing Botanical Garden, P. R. China, for providing plant materials. This work was supported by Program for New Century Excellent Talents in University (Grant No. NCET-13-0672), a Foundation for the Author of National Excellent Doctoral Dissertation of P. R. China (Grant No. 201267), the 111 Project (Grant No. B13007) and the Beijing Nova program (Grant No. Z141105001814007).
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Ju Tian and Junhao Wang have contributed equally to this work.
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Tian, J., Wang, J., Dong, L. et al. Pollen variation as a response to hybridisation in Populus L. section Aigeiros Duby. Euphytica 206, 433–443 (2015). https://doi.org/10.1007/s10681-015-1507-z
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DOI: https://doi.org/10.1007/s10681-015-1507-z