Table_1_Marker-Assisted Pyramiding of Downy Mildew-Resistant Gene Ppa3 and Black Rot-Resistant Gene Xca1bo in Popular Early Cauliflower Variety Pusa Meghna.DOCX

Cauliflower is an important extensively grown cool season vegetable in India. Black rot and downy mildew are major devastating diseases reducing yield and quality of the crop. To tackle these through host plant resistance, a marker-assisted backcross breeding method was followed to pyramid a black rot-resistant gene (Xca1bo) and a downy mildew-resistant gene (Ppa3) from donors BR-161 and BR-2, respectively, into the background of Pusa Meghna cauliflower cultivar. Marker-assisted backcross breeding was followed up to BC2 generation using SCAR marker ScOPO-04833 and SSR marker BoGMS0624 for black rot and downy mildew resistance genes in foreground selection, respectively. In background selection, at each stage of backcrossing, 47 parental polymorphic SSR markers were used. The graphical genotyping of the five two-gene (Xca1boXca1boPpa3Ppa3) homozygous BC2F2 plants showed an average recovery of 85.44% of the Pusa Meghna genome with highest genome recovery of 91.7%. The genome contribution of donor parents (BR-161 and BR-2) was 8.26 with 6.34% of residual heterozygousity. The backcross derived pyramided lines BC2F2:3-7-16 and BC2F2:3-7-33 showed high resistance to both the diseases and exhibited higher yield and vitamin C content as compared with recipient parent Pusa Meghna. It is, therefore, evident from this study that resistant genes can be introgressed successfully into a Pusa Meghna cultivar without any yield penalty, benefitting farmers with reduced input cost and consumers with chemical residue free produce. Besides, the pyramided lines carrying dominant resistant genes can be exploited in a hybridization programme to develop hybrid(s) in cauliflower.

花椰菜（Cauliflower）是印度广泛种植的重要冷季蔬菜。黑腐病与霜霉病是两大毁灭性病害，会降低该作物的产量与品质。为通过寄主植物抗性防控这两种病害，研究采用标记辅助回交育种（marker-assisted backcross breeding）策略，分别从供体亲本BR-161和BR-2中聚合抗黑腐病基因（Xca1bo）与抗霜霉病基因（Ppa3），并将其导入Pusa Meghna花椰菜品种的遗传背景中。本研究利用SCAR标记（SCAR marker）ScOPO-04833与SSR标记（SSR marker）BoGMS0624分别开展抗黑腐病与抗霜霉病抗性基因的前景选择（foreground selection），将标记辅助回交育种流程推进至回交二代（BC2）世代。在每次回交的背景选择（background selection）环节，均使用47对双亲间具有多态性的SSR标记进行基因组选择。对5株双基因纯合（Xca1boXca1boPpa3Ppa3）的BC2F2植株进行图形化基因型分析，结果显示其Pusa Meghna基因组的平均回复率为85.44%，最高基因组回复率达91.7%。供体亲本（BR-161与BR-2）的基因组贡献率为8.26%，剩余杂合性（residual heterozygosity）占比为6.34%。回交衍生的聚合株系BC2F2:3-7-16与BC2F2:3-7-33对两种病害均表现出高抗性，且相较于轮回亲本Pusa Meghna，其产量与维生素C含量更高。由此可见，本研究成功将抗性基因导入Pusa Meghna品种且未造成产量损失（yield penalty），可帮助农户降低投入成本，同时为消费者提供无化学残留的农产品。此外，携带显性抗性基因的聚合株系可应用于杂交育种计划（hybridization programme），以培育花椰菜杂交品种。