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ARS Home » Plains Area » Fargo, North Dakota » Edward T. Schafer Agricultural Research Center » Sunflower and Plant Biology Research » Research » Research Project #434618

Research Project: Fine Mapping and Developing Closely Linked Molecular Markers Associated with a Heterotic Gene for Breeding Higher Yielding Canola Lines

Location: Sunflower and Plant Biology Research

Project Number: 3060-21220-029-07-T
Project Type: Trust Fund Cooperative Agreement

Start Date: May 1, 2018
End Date: Apr 30, 2020

Objective:
This project is a continuation from the previous year where we identified a heterotic locus in the F1 hybrids between ‘Westar’ (canola, Brassica napus L.) and its chromosome segment substitution line (CSSL) introgressed with a chromosome segment in A10 of ‘Surpass 400’. The F1 hybrids, ‘Westar’ × CSSL and CSSL × ‘Westar’, increased 7% and 20% in grain yield compared to the best-parent value respectively under the growth chamber conditions. To map the heterotic gene further, we developed a set of new introgression lines (ILs) carrying different lengths of introgressed chromosome segments in A10 of ‘Surpass 400’. Eight ILs were crossed with Westar reciprocally. The resultant 16 F1 hybrids along with their parents (ILs and Westar) were planted in two locations (Fargo and Prosper, ND) using a randomized complete block design with three replicates to estimate heterotic effects. Based on phenotype data (grain yield of 16 hybrids compared to the best parent value) and genotype data (regions of those introgressed segments), we have tentatively mapped the heterotic locus within the 500 Kb region. Current task is to further verify this result and to develop more molecular markers to narrow down the target gene that causes heterosis. The overall goal of our unit research is to develop effective, environmentally sound weed management strategies in northern regions of the U.S. using winter oilseed cover crops that provide additional cash value to the farmer. Thus, development of high yielding, in addition to freezing-tolerant, canola cover crops would greatly impact U.S. canola acreage in Northern Great Plains. Current task is basically to develop more molecular markers to reduce the physical distance linking heterotic gene to within 50 Kb. The closely linked molecular markers can then be used to develop high yielding canola. To accomplish this goal, our objectives are: 1) repeat field trials by comparing the heterotic effect of eight IL groups and one CSSL group (total 36 entries) in Fargo and Prosper, 2) develop more polymorphic markers between 14.5 and 15 Mb region, and 3) fine mapping heterotic locus to be within 50 Kb physical distance for future application of the heterotic alleles.

Approach:
Objective 1. Repeating field trials: Similar trial arrangements will be used to repeat and confirm grain yield and yield-related traits in Fargo and Prosper. We will use a split plot arrangement in a randomized complete block design. There will be three replicates. Each replicate contains 9 plots (8 IL groups and 1 CSSL group), and each plot has 4 subplots (4 entries). Therefore, each replicate includes a total of 36 entries (16 IL x Westar reciprocal hybreds, 8 ILs, 8 Westar, 2 CSSL x Westar reciprocal hybreds, 1 CSSL, and 1 Westar). Each subplot is 4 feet by 7 feet. Row length is 7 feet and row space is 8 inches. Seeding space is 6 inches. Yield will be measured according to the total dry seed weight per subplot. In addition, we will select 5-10 plants from the center of each subplot to measure silique number per plant, seed number per silique, and thousand seed weight. Objective 2. Development of polymorphic markers: Since the heterotic gene was mapped in a 500 Kb region between 14.5 and 15 Mb, and we had obtained 28 homozygous recombinants previously in which crossover occurred in this region, we will apply genotyping by sequencing (GBS) in these homozygous recombinants along with Westar and CSSL to determine the length and position of the introgressed chromosome segments. To map the heterotic gene to a 50 Kb region, we will select a series of 10 homozygous recombinants, which have crossover sites that are evenly distributed between the 14.5 and 15 Mb chromosome region based on GBS results. Objective 3. Fine mapping heterotic locus: The selected homozygous recombinants (refers to as second set of introgression lines or 2nd ILs) will be crossed to Westar reciprocally to generate hybrids. The resultant hybrids together with Westar and the 2nd ILs will be phenotyped in Fargo and Prosper with three replicates. Phenotyping data on grain yield, silique number per plant, seed number per silique, and thousand seed weight will be collected. The mapping of the target gene will be determined by genetic linkage and phenotypic analysis, and the mapping information can be used to annotate candidate heterotic genes and develop gene specific markers.