Wen Yanbin, Liu Hongjiu, Meng Huanwen, Qiao Lijun, Zhang Guoqing, Cheng Zhihui
College of Horticulture, Northwest A&F University, Xianyang, China.
Development Center of Fruit Vegetable and Herbal Tea, Datong, China.
Front Plant Sci. 2022 Jun 22;13:917910. doi: 10.3389/fpls.2022.917910. eCollection 2022.
Garlic ( L.) is a compelling horticultural crop with high culinary and therapeutic values. Commercial garlic varieties are male-sterile and propagated asexually from individual cloves or bulbils. Consequently, its main breeding strategy has been confined to the time-consuming and inefficient selection approach from the existing germplasm. Polyploidy, meanwhile, plays a prominent role in conferring plants various changes in morphological, physiological, and ecological properties. Artificial polyploidy induction has gained pivotal attention to generate new genotype for further crop improvement as a mutational breeding method. In our study, efficient and reliable induction protocols of autotetraploid garlic were established by applying different antimitotic agents based on high-frequency direct shoot organogenesis initiated from inflorescence explant. The explants were cultured on solid medium containing various concentrations of colchicine or oryzalin for different duration days. Afterward, the ploidy levels of regenerated plantlets with stable and distinguished characters were confirmed by flow cytometry and chromosome counting. The colchicine concentration at 0.2% (w/v) combined with culture duration for 20 days was most efficient (the autotetraploid induction rate was 21.8%) compared to the induction rate of 4.3% using oryzalin at 60 μmol L for 20 days. No polymorphic bands were detected by simple sequence repeat analysis between tetraploid and diploid plantlets. The tetraploids exhibited a stable and remarkable dwarfness effect rarely reported in artificial polyploidization among wide range of phenotypic variations. There are both morphological and cytological changes including extremely reduced plant height, thickening and broadening of leaves, disappearance of pseudostem, density reduction, and augmented width of stomatal. Furthermore, the level of phytohormones, including, indole propionic acid, gibberellin, brassinolide, zeatin, dihydrozeatin, and methyl jasmonate, was significantly lower in tetraploids than those in diploid controls, except indole acetic acid and abscisic acid, which could partly explain the dwarfness in hormonal regulation aspect. Moreover, as the typical secondary metabolites of garlic, organosulfur compounds including allicin, diallyl disulfide, and diallyl trisulfide accumulated a higher content significantly in tetraploids. The obtained dwarf genotype of autotetraploid garlic could bring new perspectives for the artificial polyploids breeding and be implemented as a new germplasm to facilitate investigation into whole-genome doubling consequences.
大蒜（L.）是一种极具吸引力的园艺作物，具有很高的烹饪和治疗价值。商业大蒜品种是雄性不育的，通过单个蒜瓣或珠芽进行无性繁殖。因此，其主要育种策略一直局限于从现有种质中进行耗时且低效的选择方法。与此同时，多倍体在赋予植物形态、生理和生态特性的各种变化方面发挥着重要作用。人工多倍体诱导作为一种诱变育种方法，已成为产生新基因型以进一步改良作物的关键关注点。在我们的研究中，基于从花序外植体起始的高频直接芽器官发生，通过应用不同的抗有丝分裂剂，建立了高效可靠的同源四倍体大蒜诱导方案。将外植体在含有不同浓度秋水仙碱或安磺灵的固体培养基上培养不同天数。之后，通过流式细胞术和染色体计数确认具有稳定且显著特征的再生植株的倍性水平。与使用60 μmol L安磺灵处理20天诱导率为4.3%相比，0.2%（w/v）秋水仙碱浓度结合培养20天的诱导效果最佳（同源四倍体诱导率为21.8%）。通过简单序列重复分析，在四倍体和二倍体植株之间未检测到多态性条带。四倍体表现出稳定且显著的矮化效应，在广泛的表型变异中，这种效应在人工多倍体化中很少被报道。存在形态和细胞学变化，包括植株高度极度降低、叶片增厚加宽、假茎消失、密度降低以及气孔宽度增加。此外，除吲哚乙酸和脱落酸外，四倍体中包括吲哚丙酸、赤霉素、油菜素内酯、玉米素、二氢玉米素和茉莉酸甲酯在内的植物激素水平显著低于二倍体对照，这在激素调节方面可以部分解释矮化现象。此外，作为大蒜的典型次生代谢产物，包括大蒜素、二烯丙基二硫化物和二烯丙基三硫化物在内的有机硫化合物在四倍体中显著积累了更高的含量。所获得的同源四倍体大蒜矮化基因型可为人工多倍体育种带来新的视角，并作为一种新的种质用于促进对全基因组加倍后果的研究。
