title: 2n megagametophyte formed via SDR contributes to tetraploidization in polyembryonic 'Nadorcott' tangor crossed by citrus allotetraploids.
abstract: 2 n megagametophyte formation plays an important role in polyploidization in polyembryonic citrus and is valuable for plant improvement. Tetraploid plants are frequently observed in the seedlings of diploid polyembryonic citrus genotypes. However, the mechanisms underlying the formation of tetraploids are still indistinct when apomictic citrus genotypes are used as female parent to cross with tetraploids. Herein, 54 tetraploid progenies, which were unexpectedly obtained previously from four 2x × 4x crosses using polyembryonic 'Nadorcott' tangor as seed parent, were analyzed by 22 simple sequence repeat (SSR) markers, aiming to reveal their genetic origin and the mechanism underlying 2n megagametophyte formation. The results showed that 13 tetraploids from all these four crosses were doubled diploids as indicated by their identical SSR allelic profile with their female parent; while the remaining 41 tetraploids apparently exhibited paternally derived alleles, which confirmed their zygotic origin. Furthermore, the genotyping of all hybrids indicated that all of them arose from 2n megagametophytes. Based on the genotypes of 2n megagametophytes, the analysis of maternal heterozygosity restitution (HR) for each marker showed that it varied from 0.00 to 87.80 % with a mean value of 40.89 %. In addition, it was observed that 13 markers displayed a lower rate than 50 %. On the basis of the above results, it can be speculated that the second division restitution (SDR) is the mechanism underlying the 2n megagametophyte formation in 'Nadorcott' tangor. The elucidation of the mechanism of 2n megagametophyte formation will be of great help to optimize further sexual hybridization for polyploids in citrus.
authors: Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan, 430070, China.
authors: Kai-Dong
authors: KD
authors: Xie
authors: Xiao-Pei
authors: XP
authors: Wang
authors: Manosh Kumar
authors: MK
authors: Biswas
authors: Wu-Jun
authors: WJ
authors: Liang
authors: Qiang
authors: Q
authors: Xu
authors: Jude W
authors: JW
authors: Grosser
authors: Wen-Wu
authors: WW
authors: Guo
mesh_terms: D002957:Citrus / Q000235:genetics*; D004171:Diploidy; D005838:Genotype; D036226:Seedlings / Q000235:genetics; D057891:Tetraploidy