Abstract
The development of new improved varieties is one of the major goals of plant breeding. Concomitantly, the demand for stable, eco-friendly, and high-quality rice production is constantly increasing. However, most farmers prefer to cultivate familiar rice varieties developed more than 10 years ago to minimize economic risk. A strategy is needed to develop rice varieties without the limitations of the preferred old varieties. Here, we tested the rapid development of near isogenic lines (NILs) using a rapid generation advance system together with marker-assisted backcrossing to overcome the shortcomings of parental materials. For this purpose, we chose rice stripe virus (RSV) susceptible variety Unkwang and RSV resistant variety Haedamssal as experimental materials. First, we backcrossed and screened BC1F1 and BC2F1 plants having similar agronomic traits as Unkwang and the heterozygous genotype for RSV resistant specific marker InDel7 from Haedamssal. Secondly, the genetic background of 11 BC2F1 plants was identified with 73 KASP markers; plants of line YR32548-8 showed 84.5% of recovery of the recurrent parent genome. Among 28 BC2F2 plants, YR32548-8-16 was the line that showed maximum recovery of the recurrent parent genome (96.2%) while effectively introgressed with RSV-resistance loci on chromosome 11. Finally, we selected line YR32548-8-16 as an NIL showing an RSV resistant phenotype and similar agronomic traits to Unkwang. This fast breeding approach will be useful in rice breeding programs for the improvement of varieties preferred by farmers for their stress tolerance, yield, or quality.
Highlights
Background selection for rapidrecurrent parent genome (RPG) recovery will be extremely useful if backcrossing is continued in a greenhouse or under a non-target environment [36]
When we tested the genotypes of these 22 plants using InDel7, which is tightly linked with rice stripe virus (RSV) resistance for foreground selection, 10 plants showed the heterozygous genotype for InDel7 and 12 plants held the same allele as the susceptible recurrent parent, Unkwang (Fig 2)
The conventional breeding method usually takes 3–4 years to develop genetically fixed lines [43] but, we developed homozygous near isogenic lines (NILs) in the BC2F2 generation within three years and our selected NILs showed a high level of resistance against RSV, with an infection ratio lower than 30% (Fig 4D)
Summary
Background selection for rapidRPG recovery will be extremely useful if backcrossing is continued in a greenhouse or under a non-target environment [36]. Conventional gel-based markers including SSR and SNP markers were widely used for background selection for RPG recovery in MABC [37,38,39] These marker systems showed low resolution and density for whole genome coverage and were labor-intensive and time-consuming. 506 KASP markers based on SNP were established for genotyping Korean japonica rice varieties by another research group working at our institute [5] We applied this 506 KASP-marker-set for rapid background selection at each generation and identified 22% of KASP markers showing polymorphism between Unkwang and Hadamssal. Among 28 plants screened for the homozygous resistant genotype in the BC2F2 generation, line YR32548-8-16, showing 96.2% recovery of RPG, was screened through second background selection (S3 Table). Target loci for RSV on chromosome 11 were introduced in line YR32548-8-16
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