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Agriculture and Agri-Food Canada, Research Centre, 6000 C & E Trail, Lacombe, AB T4L 1W1
Corresponding author (kibites{at}em.agr.ca)
Seven pairs of near-isogenic lines of oat (Avena sativa L.) (Reg. no. GP-57 to GP-70, PI 613330 to PI 613343) were developed by the Agriculture and Agri-Food Canada Research Centre, Lacombe, AB Canada, and released in 1999. Each pair is near-isogenic except for the alleles conferring dwarf (Dw6/Dw6) and normal (dw6/dw6) plant height. Table 1 shows identification, agronomic and grain quality data for the seven pairs of near-isogenic lines.
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The seven pairs of near-isogenic lines were developed using a program of single-seed descent. The crosses were made at the Lacombe Research Centre in 1991. The F1 through F6 generations were grown in growth chambers (Conviron PG36; Controlled Environment, Inc., Winnipeg, MB) under 16-h photoperiod (450 µmol m-2 s-1 photosynthetic photo flux density) and a thermoperiod of 21/15°C that was in phase with the photoperiod. The F7 and subsequent generations were grown in the field on a Penhold silt-loam (coarse loamy, mixed, frigid, Typic Haplustall) soil. In the F2 through F8 generations of single-seed descent, heterozygosity was maintained at the Dw6/dw6 locus while homozygosity was achieved at all other loci. Since the Dw6 gene is inherited as a single dominant gene (Brown et al., 1980), heterozygotes were identified by selection for dwarf (Dw6/-) phenotype combined with progeny testing to verify segregation for height. The single-seed descent program was terminated at the end of the F8 generation, at which time 
20 seeds were harvested from each heterozygous plant and space-planted to produce the F9 generation. In the F9 generation, two tall (dw6/dw6) and six to eight short (Dw6/-) plants, all originating from a single F8 plant were selected. Seed from individual F9 plants was harvested separately and sown in a plant-to-row nursery to produce F8 derived F10 (F8:10) families. In the F8:10 generation one family homozygous for the dwarf allele (Dw6/Dw6) and another family homozygous for the normal height (dw6/dwR6) allele, both originating from a single F8 plant, were selected. Seed from these two families were bulked to constitute the near-isogenic pairs. This process was repeated for each pair of near-isogenic lines. Thus, each pair of near-isogenic lines traces to a single F8 plant, which in turn traces to a single F2 plant.
Each of the 14 lines was inbred for at least eight generations. In the absence of selection and/or linkage and after eight generations of single-seed descent (self-pollination), two members of a pair of near-isogenic lines will be expected to be very similar to each other, having about 99.6% of their germplasm in common, and differing at only about 0.4% of their loci; however, when the seven pairs of near-isogenic lines were grown at three locations (Lacombe, Douglas Farm and Breton) in central Alberta in 1997 and 1998, significant differences were observed both within and among pairs of near-isogenic lines. The average effect of the Dw6 gene across the seven pairs was to delay panicle emergence by about 6 d, to delay maturity by about 4 d, and to reduce plant height and grain yield by 33.8 and 18.1%, respectively. It also increased lodging resistance, but reduced test weight by 5.2 kg hL-1, and kernel weight by an average of 6.7 mg/kernel (Table 1). These results indicated that the Dw6 gene may have a pleiotropic effect on genes governing several traits including grain yield, number of days to panicle emergence, number of days to mature, test weight, kernel weight and lodging resistance. An alternative explanation for the differences other than height within pairs of nearly-isogenic lines may be that the genes governing and/or modifying the above traits were tightly linked to the Dw6/dw6 locus and were transferred intact (i.e., without recombination) from the Dw6 and dw6 donor parents to the respective dwarf and normal height progeny. After eight generations of self-pollination, and concurrent selection for heterozygosity, a segment of the parental chromosome, about 7.1 cM in length would be expected to remain intact around the Dw6/dw6 locus (Hanson, 1959). If there is interference from the centromere and/or if the chromosome carrying the Dw6/dw6 locus is short, the size of the parental-type chromosome segment that would have remained intact after eight generations of self-pollination will be longer than 7.1 cM. Thus, the observed differences within pairs of near-isogenic lines may also be related to the size of the parental-type chromosome segments that despite eight generations of self-pollination may have remained intact and were inherited by the dwarf and tall near-isogenic lines.
The seven pairs of near-isogenic lines were developed for comparative research of dwarf and normal height genotypes and have not been screened for disease resistance or agronomic performance. All seven pairs are spring type and do not have vernalization requirements. They have shown disease reactions similar to cultivars commonly grown in the disease-free areas of western Canada (primarily Alberta and western Saskatchewan). They are resistant to Victoria blight [caused by Bipolaris victoriae (F. Meehan & Murphy) Shoemaker], moderately susceptible to smuts [caused by Ustilago avenae (Pers.) Rostr., and U. kolleri Wille.], and barley yellow dwarf virus (BYDV), and susceptible to oat crown rust (caused by Puccinia coronata Corda var. avenea W.P. Fraser & Ledingham), and oat stem rust (caused by P. graminis Pers.:Pers. f. sp. avenae Eriks & E. Henn.).
The seven pairs of near-isogenic lines were released as germplasm for research purposes. They may offer unique germplasm for quantifying the agronomic value of the Dw6 gene and to determine the genetic and biochemical basis of dwarfism in oats. They will also be useful in genomics and proteomics studies and for molecular characterization and mapping of the Dw6 gene.
Seed of the seven pairs of near-isogenic lines are stored at the Plant Gene Resources of Canada, Agriculture and Agri-Food Canada, Saskatoon Research Centre, 107 Science Place, Saskatoon, SK S7N 0X2, and at the USDA National Seed Storage Laboratory, Fort Collins. Small quantity (5 g) of seed of each line may be obtained from the author for at least 5 yr from the date of this publication. Seed will be sent upon a written request and agreement to recognize the seed source when these near-isogenic lines are used in research or publications, or in the development of new cultivars and germplasm.
ACKNOWLEDGMENTS
The author gratefully acknowledges the technical assistance of Don Beauchesne, Bruce Wendel and Patty Reid. This study was funded in part by a research grant from the Quaker Oats Company of Canada.
NOTES
Contribution no. 928. Registration by CSSA.
Accepted for publication June 30, 2000.
REFERENCES
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