Triploid in Poaceae: Formation, Detection, and Utilization

doi:10.11983/CBB20166

Abstract

Abstract: The formation pathway of triploid in Poaceae includes 2n gamete fusion, interploidy cross, polyspermy, and endosperm culture. The fusion of reduced male (n) and unreduced female gamete (2n) is the main method for forming natural triploids. Interploidy cross is the main method for synthesizing artificial triploids. The application of ploidy identification methods such as morphological observation, chromosome analysis, flow cytometry and molecular markers in gramineous triploids is introduced, and the advantages and disadvantages of different methods are also discussed. At present, triploid has no direct application value in cereal crops, but it can be used as a genetic bridge to synthetize polyploid and aneuploid, as well as to transfer alien genes from wild species to cultivated species. Gramineous triploids (especially allotriploid) are widely cultivated for forage or biofuel production, suggesting that triploidy breeding may be directly performed in this type of grasses. We discuss the future prospect of research on gramineous triploid, e.g., polyploid- and apomixis-triploid breeding. Particularly, endosperm culture can synthesize triploids in one step, and polyspermy can achieve one-step fusion of three genetically different plant genomes, which should be paid attention to in the triploidy research. Due to rare occurrence of 2n gamete fusion and polyspermy, and frequent chromosomal variation in ploidy hybridization and endosperm culture, the development of high-throughput triploid identification technology will become the key for breakthrough in triploidy generation/breeding.

Key words: triploid, 2n gamete, interploidy cross, endosperm culture, polyspermy, breeding program

Xu Yan, Yanchun Zuo, Honglin Wang, Yang Li, Yingzheng Li, Jing Kou, Qilin Tang, Xiaokang Zhou, Zhouhe Du. Triploid in Poaceae: Formation, Detection, and Utilization[J]. Chinese Bulletin of Botany, 2021, 56(3): 372-387.

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URL: https://www.chinbullbotany.com/EN/10.11983/CBB20166

https://www.chinbullbotany.com/EN/Y2021/V56/I3/372

Figures/Tables 4

Figure 1 Pathways to triploidy formation in Poaceae (A) A sperm fertilizes an egg cell to produce diploid zygote which subsequently grows into diploid embryo; (B) A sperm fertilizes a center cell to produce triploid primary endosperm cell which subsequently grows into endosperm; (C) The embryo develops into diploid plant through in vitro culture or seed germination; (D) The endosperm develops into triploid plant via culturing in vitro; (E) Triploid formation by a 2n+n mating; (F) The autotriploid hybrid produced by crossing tetraploid (2n=4x=AAAA) and diploid (2n=2x=AA); (G) The allotriploid hybrid produced by crossing tetraploid (2n=4x=AAAA) and diploid (2n=2x=BB); (H) Formation of triploid by polyspermy

Figure 2 Mechanisms of 2n gamete formation (A) Chromosome numbers of normal gametes are halved compared with somatic cells; (B) PRD (pre-meiotic doubling) gametes are obtained as a result of the tetraploid pollen mother cells formed by cytomixis or syncytium, e.g., Dactylis glomerata (Falistocco et al., 1995); (C) In the FDR (first division restitution) type, pairing and division of homoeologous chromosomes do not occur during meiosis I, and the FDR 2n gametes maintain all of their parental genes except cross-over fragments, e.g., Paspalum jesuiticum (Filho et al., 2014) and Lolium perenne (Chen et al., 1997); (D) SDR (second division restitution) gametes with two copies of non-recombinant chromosomes are the result of the second division omission or cytokinesis abnormalities after normal anaphase II, e.g., L. perenne (Chen et al., 1997); (E) IMR (indeterminate meiotic restitution) gametes were discovered in Lilium longiflorum × Asiatic hybrid (Lim et al., 2001), in which some chromosomes are separated as univalents during meiosis I whereas the others are separated as bivalents, and subsequently the second division omission occurs during meiosis II; (F) PMD (post-meiotic doubling) gametes occurs due to the genome doubling of haploid spores during microgametogenesis, e.g., Solanum tuberosum (Bastiaanssen et al., 1998)

Table 1 Triploidy cultivars in Poaceae

母本	父本	品种名	用途	参考文献
狗牙根(Cynodon dactylon) 2n=4x=36	非洲狗牙根(C. transvaalensis) 2n=2x=18	Tifway、TifwayII、Midiron、TifEagle、Tifgreen、Tifdwarf、MS-Supreme、MS-Express、TifSport和Champion (2n=3x=27)	草坪草	Kamps et al., 2011
荻(Miscanthus sacchariflorus) 2n=4x=76	芒(M. sinensis) 2n=2x=38	Illinois和Freedom (2n=3x=57)	能源作物	Perera et al., 2015
玉米(Zea mays) 2n=2x=20	四倍体大刍草(Z. perennis) 2n=4x=40	玉草1号(2n=3x=30)	饲用作物	任勇等, 2007
指状摩擦禾(Tripsacum dactyloides) 2n=2x=36	指状摩擦禾(T. dactyloides) 2n=4x=72	Verl (2n=3x=54)	饲用作物	Springer et al., 2006
薏苡(Coix lacryma-jobi) 2n=2x=20	水生薏苡(C. aquatica) 2n=4x=40	丰牧88 (2n=3x=30)	饲用作物	孙福艾, 2017
象草(Pennisetum purpureum) 2n=4x=28	美洲狼尾草(P. americana) 2n=2x=14	热研4号(2n=3x=21)	饲用作物	刘国道等, 2012
美洲狼尾草(P. americana) 2n=2x=14	象草(P. purpureum) 2n=4x=28	闽牧6号和华南1号(2n=3x=21)	饲用作物	陈平等, 2004; 陈钟佃等, 2012

Figure 3 Application of triploid in Poaceae (A) The direct use of triploid cultivar; (B) The improvement of triploid cultivar through techniques such as radiation, genetic modification, or tissue culture; (C) Use of “triploids bridge” for production of polyploids; (D) Alien genes transfer; (E) Development of aneuploidy by 3x/2x mating

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