Pollen variation as a response to hybridisation in Populus L. section Aigeiros Duby

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 9 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.

High frequency 2n pollen formation in black poplar (Populus nigra L.) induced by colchicine

“…Perpendicular spindle (Fig. 4F) in this study presented as a cross and chromosomes were compline which was distinct from other studies (Zhang and Kang, 2010;Tian et al, 2015). Besides, we observed other various abnormalities such as unseparated cytoplasm (Fig.…”

“…Aigeiros, production of 2n pollen was lower than the two hybrids mentioned above (55.67%) (Zhang, 2006). Hybrids, some of which can produce natural 2n pollen, were chosen in many studies and had favorable performance in artificial induction probably because of their unstable genomes that may be doubled more easily (Kang, 2002;Zhang and Kang et al, 2010;Tian et al, 2015). Research on original species in Populus is still at an early stage, and the cytological mechanisms of unreduced gametes formation are not clear.…”

Abnormal meiosis in an intersectional allotriploid of Populus L. and segregation of ploidy levels in 2x × 3x progeny

“…italica , abnormal meiotic phenomena such as multinuclei, multinucleoli, monads, dyads, and polyads have been observed [ 49 ]. Previous studies on diploid Populus hybrids also showed that hybridization tends to induce occurrence of meiotic abnormalities [ 45 , 50 ]. However, compared with the diploid species and hybrids of Populus , although meiosis in ‘Yinzhong’ showed similar abnormalities, the frequency of abnormalities was high in ‘Yinzhong’, suggesting that more abnormalities might be induced by its distant genomic composition and polyploidization.…”

“…Production of unreduced gametes has been reported in many species and hybrids of the genus Populus [ 44 , 45 , 50 – 54 ]. There are multiple cytological mechanisms of unreduced gamete formation, which have been reviewed frequently [ 55 , 56 ].…”

Relationship between meiotic instability and fertility in F2 generation Arabusta coffee plants

“…2). Maich et al (1999) and Tian et al (2015) verified in wheat that there is not always a significant relationship between a high meiotic index value and high fertility. This contradiction could be explained by some mechanisms that act in the final phases of meiosis, meaning that univalents and laggards are inserted in the nuclei of tetrads instead of forming micronuclei, thus increasing the frequency of quartets of tetrads with normal nuclei (Gaur et al 1983).…”