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Selective Recombination Close to the Semi-dwarfing Locus Through Bulk- Population in the Hybrid Between Triticum Aestivum and Triticum Polonicum

Md. Anowarul Haque
School of Agriculture and Rural Development, Bangladesh Open University, Gazipur- 1705

Abstract/ Executive Summary:

The Rht-B1 locus on the short arm of chromosome 4B has multiple alleles that give phenotypic expressions ranging from semi-dwarfism to extreme dwarfism. Allelic variation at Rht-B1 locus was also found in semi-dwarf Triticum polonicum L. cv. IC12196. The semi-dwarf allele from IC12196 could be an alternative source of reduced height gene. The experimental lines derived from the cross between Triticum aestivum L. cv. Novosibirskaya 67 (N67) and IC12196 were analyzed concerning the introgression of semi-dwarf allele from IC12196. The aim of the present study was to assess the selection for the semi-dwarfism and recombination around the locus of semi-dwarf gene using microsatellite markers on the short arm of chromosome 4B. The Rht-IC12196 allele was allelic to Rht-B1b allele, and microsatellite markers indicated that the Rht-IC12196 allele was linked with the markers, Xbarc1045 and Xgwm113 on the short arm of chromosome 4B. Out of 112 hexaploid introgression lines, 29 lines were semi-dwarf. The Xgwm113 and Xhbg226 markers flanking the Rht-B1 locus were replaced by N67 allele in the majority of introgression lines. Although it did not intend, the region around the Rht-B1 locus was highly selectable, but on short arms of chromosome 4B, Rht-IC12196 gene near the locus Xgwm113 explained a large part of the phenotypic variation originated from N67-allele and non-parental allele in tall accessions. The Rht-B1a allele was favorable in the consequence of bulk population breeding and the frequency of Rht-B1a allele was 73% in the hexaploid introgression lines.

Keywords: Bulk-population, Introgression, Microsatellite markers, Recombination, Wheat

Location:

Start Date:

End Date:

Program Area: Variety and Species

Commodity: Wheat

Objectives:

The aim of the study was to assess the selection and recombination for the semi-dwarfism in the progenies between T. aestivum and T. polonicum using microsatellite markers on the short arm of chromosome 4B.

Methodology:

Plant materials

To map the GA₃-insensitive semi-dwarf gene, tentatively designated as Rht-IC12196, and microsatellite markers on chromosome 4BS, produced F₂ hybrid of T. aestivum ‘Novosibirskaya 67 (N67)’ - T. polonicum ’IC12196’ and F₂ hybrids of T. polonicum ’IC12196’/Triticum durum Desf. ‘LD222’. Plant height of LD222 was tall. To investigate the allelic relationship between Rht-IC12196 and Rht-B1b alleles, F₂ hybrids of T. polonicum ’IC12196’/T. durum ’Cando’ were also obtained. Cando has the Rht-B1b allele derived from Norin 10. Using the F₂ generation of N67/IC12196, a small-scale bulk breeding method was applied to develop introgression lines. The procedure was described by Kosuge et al. (2010). Two hundred F₂ plants were grown in an area of 20 m². All the seeds were harvested from the F₂ plants as a bulk. Subsequently, 200 F₃ seeds were randomly chosen from the bulk, and were grown in the same area size in the subsequent cropping cycle. This method was applied until reaching the bulked F₆ generation. Single seed descents of 132 F₆ plants were used to advance the population from F₇ through F₁₀ generation. One-hundred and twelve hexaploid F₁₀ lines were available for the present experiment. All populations were grown in the experimental field at the College of Agriculture, Ibaraki University, Japan. Culm lengths of individuals were measured after ripening

Microsatellite mapping of the Rht-IC12196 and allelic composition of the experimental lines

An intended to map of Rht-IC12196 using the F₂ hybrid of N67/IC12196. However, it was found that segregation for plant height showed irregularity probably due to aneuploidy in the F₂ generation. The chromosome numbers of the F₂ of N67/IC12196 was expected to vary from 2n = 28 to 42, depending on the transmission of the D-genome univalents (Alston and Jones, 1968). Alternatively, there are used F₂ hybrids of IC12196/LD222 to establish a template linkage map of chromosome 4BS including the semi-dwarf locus. It was expected that the ratio of IC12196 and non-IC12196 (N67 and non-parental) allele at the given locus would be 1:1 in the F₁₀ generation provided there was lower natural selection during segregating generations. It was supposed non-parental allele was caused by a spontaneous mutation at the given locus. Genomic DNA was extracted from seedling leaves of N67, IC 12196, LD222, F₂ hybrids of IC12196/LD222 and 112 hexaploid introgression lines, according to Dellaporta et al. (1983). To map the Rht-IC12196 gene and allelic composition of the introgression lines, used the wheat Xgwm, Xbarc and Xhbg microsatellite markers located on chromosome 4BS. The Xgwm microsatellite markers were developed by Röder et al. (1998). The Xbarc and Xhbg microsatellite markers were available from Song et al., (2005) and Torada et al. (2006), respectively. The PCR conditions, electrophoresis of PCR products and detection of amplified fragments followed Kosuge et al. (2008). Multipoint linkage values were calculated using Map Manager QTX (Manly et al., 2001). Minimum LOD scores of >3.0 were used to develop the linkage map. The software calculated genetic distances in centiMorgans (cM) by applying the Kosambi (1944) mapping function.

Source of Information: J Bangladesh Agril Univ 17(2): 148–152, 2019

Article Link (Online Journal): https://doi.org/10.3329/jbau.v17i2.41937

Funding Source:

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Total Budget (Tk.) :

Achievement/Findings:

Strong selection within a given population locally reduces genetic variability not only in the selected gene itself but also in neighboring loci. This effect is related to the initial linkage disequilibrium between markers and the selected gene. It depends mainly on the number of copies of the beneficial allele at the beginning of the selection phasel. Under a small-scale bulk breeding method, taller plants were favored against shorter plants determined by Rht-IC12196. Although I did not intend it, the region around the Rht-B1 locus was highly selectable, and the Rht-B1a allele was favorable in the process of bulk- population selection. The frequency of Rht-B1a allele was 73% in the hexaploid lines. Except for the four introgression lines, 7029, 7041, 7018 and 7007, the frequency of N67-alleles is extremely low in the short arm of chromosome 4B. Most of the crossovers (90%) occurred in the distal sub- telomeric regions that illustrated fifty percent of the chromosome. A very weak crossover frequency was observed on the proximal regions nearby the centromere. Although there are need more polymorphic markers for further resolution, this experimental analysis indicated that the region around the Rht-B1 locus was highly selectable. The application of the bulk breeding method to introduce reduced height gene indicated not only the characteristics of recombination on the short arm of chromosome 4B, but also the relatively strong natural selection around Rht-B1 locus. Thus, the allelic combination around Rht-IC12196 locus was dominated by N67-allele in the semi-dwarf introgression lines, which may be possible breeding materials.

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