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Dep. of Plant Sciences, University of California, Davis, CA 95616-8515
* Corresponding author (jdubcovsky{at}ucdavis.edu)
We report here the release of four germplasm lines of hard red spring (HRS) wheat (T. aestivum L.) [Yecora Rojo Yr36– Gpc-B1 (Reg. no. GP-793, PI 638740), Yecora Rojo Lr47 (Reg. no. GP-791, PI 638738), Kern Lr47 (Reg. no. GP-792, PI 638739), and Anza Lr37/Yr17/Sr38 (Reg. no. GP-795, PI 638742)] and one durum wheat (T. turgidum L.) [UC1113 Yr36– Gpc-B1 (Reg. no. GP-794, PI 638741)], isogenic for leaf rust (Puccinia triticina Eriks.) resistance gene Lr47, stripe rust (P. striiformis West. f. sp. tritici) resistance gene Yr36, and the Lr37/Yr17/Sr38 leaf, stripe, and stem rust (P. graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn.) resistance gene complex. All genes were transferred by six backcrosses to their respective recurrent parents and molecular markers for each gene were used to select heterozygous plants for the targeted genes. After the sixth backcross plants were self-pollinated and homozygous BC6F2 plants were selected using markers. The isogenic lines are expected to be more than 99% identical to their recurrent parents.
Isogenic Lines for Stripe Rust Resistance Gene Yr36 and Grain Protein Content Gene Gpc-B1
Chromosome 6B from T. turgidum ssp. dicoccoides (Körn.) Thell. accession ‘FA15–3’ from Israel (DIC hereafter) carries a gene that significantly increases grain protein content (Cantrell and Joppa, 1991). This gene was initially mapped as a quantitative trait locus within a 30-cM region of the short arm of chromosome 6BS using Recombinant Substitution Lines (RSLs) of the DIC 6B chromosome in the genetic background of Langdon (Joppa et al., 1997). The same DIC chromosome segment was found in the hexaploid wheat variety ‘Glupro’ (‘Columbus’/T. turgidum var. dicoccoides//‘Len’) (Khan et al., 2000; Mesfin et al., 1999). The gene responsible for the differences in grain protein content was mapped as a single locus designated Gpc-B1 proximal to the Nucleolar Organizer Region (Olmos et al., 2003; Distelfeld et al., 2004).
During field evaluations of the RSLs at University of California (UC) at Davis (Olmos et al., 2003), we observed that the lines with the DIC segment were more resistant to stripe rust than the lines with the Langdon segment. Two RSLs with the DIC 6BS region and two with the Langdon region were evaluated under controlled conditions at Washington State University. At the seedling stage, all lines were susceptible to the 15 different stripe rust races tested (including new races PST100 and PST101), but when the same lines were evaluated at the adult plant stage under a high-temperature cycle, the lines carrying the DIC segment showed significantly lower infection types (IT: 2.0 to 2.3) than the lines with the Langdon segment (IT: 7.0 to 7.3) with races PST100 and PST101. This high-temperature adult plant resistance gene was mapped as a single locus designated Yr36 (McIntosh et al., 2005). Yr36 was mapped on chromosome 6BS, 2 to 4 cM proximal to the Gpc-B1 gene (Uauy et al., 2005).
Distal molecular markers Xucw74 and proximal markers Xucw77 or Xbarc136 were used to introgress Yr36 and Gpc-B1 into the HRS common wheat variety ‘Yecora Rojo’ CItr 17414 (Qualset et al., 1985) using Glupro as a donor parent; and into the durum breeding line UC1113 (UC Davis selection from CIMMYT cross CD52600 [KIFS//RSS/BD1419/3/MEXIS-CP/4/WAHAS/5/YAV79]) using Langdon RSL#65 as a donor parent. The BC6F3 seeds of the homozygous lines were deposited at the National Small Grains Collection (NSGC) as Yecora Rojo Yr36– Gpc-B1 and UC1113 Yr36– Gpc-B1. These isogenic lines have been designated as the type germplasm for the Yr36 gene in T. aestivum and T. turgidum respectively (McIntosh et al., 2005).
The two pairs of isogenic lines were compared in field trials in Madera, CA, and Davis, CA, in 2004 under severe stripe rust infection pressure using a split plot design with five replications and large plots (1.2 by 4.0 m in Davis and 1.5 by 4.0 m in Madera). Lines with and without Yr36– Gpc-B1 showed no significant differences in height and heading time for both the tetraploid and hexaploid pairs of isogenic lines.
The Yecora Rojo Yr36-Gpc-B1 line showed a significant reduction in stripe rust infections (from 87 to 51% severity, Davis P = 0.20, Madera P < 0.0009), higher yields (average increase of 970 kg ha–1, Davis P = 0.05, Madera P = 0.02), and an average increase of 850 g protein per 100 kg of grain relative to the isogenic line without the DIC 6BS chromosome segment (from 13.2 to 14.1% protein content, Davis P = 0.03, Madera P = 0.0007). Test weights of the lines with the Yr36-Gpc-B1 genes (79.3 ± 0.5 kg hL–1) and without these genes (78.8 ± 0.9 kg hL–1) were not significantly different in this experiment.
The UC1113 Yr36-Gpc-B1 line showed a significant reduction in stripe rust severity (from 36 to 2% severity, Davis P = 0.03, Madera P = 0.006), slightly higher yields (average increase of 242 kg ha–1, although not significant in both locations), and an average increase of 1100 g of protein per 100 kg of grain relative to the isogenic line without the DIC 6BS chromosome segment (from 13.5 to 14.5% protein content, Davis P = 0.006, Madera P < 0.0001). Test weights of the lines with the Yr36-Gpc-B1 genes (80.1 ± 0.5 kg hL–1) and without these genes (81.0 ± 0.5 kg hL–1) were not significantly different in this experiment.
Isogenic Lines for Leaf Rust Resistance Gene Lr47
The interstitial translocation line T7AS-7S#1–7AS·7AL carrying Lr47 from T. speltoides (Tausch) Gren. was originally transferred to bread wheat by irradiating hybrid seed (CI15092/T. speltoides//‘Fletcher’/3/5* ‘Centurk’) with fast neutrons (Wells et al., 1982). Interstitial segments of chromosome 7S#1 were transferred to chromosome 7A of hexaploid wheat using the ph1b mutation that promotes homeologous recombination (Lukaszewski 1995). The interstitial translocations were backcrossed three times into hard white spring variety ‘Pavon 76’ (PI 519847) and plants homozygous for the interstitial translocation were released as germplasm PI 603918 (Lukaszewski et al., 2000).
Resistance gene Lr47 for leaf rust conferred resistance to the leaf rust races TBT, NBB, MBR, LCG, SDJ, MBG, NDB, MCG, and TDD (PRT codes, Long and Kolmer, 1989). The T. speltoides segment is located 2 to 10 cM from the centromere and is 20 to 30 cM long (Dubcovsky et al., 1998). This segment is generally transferred as a single linkage block. Here we report the transfer of the Lr47–T. speltoides segment from Pavon 76 into HRS varieties Yecora Rojo and ‘Kern’ (PI 612142) using molecular markers (Helguera et al., 2000).
The BC6F3 seeds of the homozygous lines were deposited at the National Small Grains Collection (NSGC) as Yecora Rojo Lr47 and Kern Lr47. The two pairs of isogenic lines were compared in field trials at Kings, CA, in 2003 and Kings and UC Davis, CA, in 2004 using a split plot design with four replications [plot size (1.2 by 4.0 m in Davis and 1.5 by 4.0 m in Kings)]. Isogenic lines with and without the gene showed similar agronomic characteristics including height and heading time. Depending on the environment, some of the plants carrying the Lr47 chromosome segment showed purple stems in some plants.
No significant differences in yield between isogenic lines with and without the Lr47 gene were detected at Kings. However, at UC Davis under strong stripe rust infection pressure, the lines with the leaf rust resistance gene Lr47 showed increased stripe rust infections (81 to 91% increase in severity for Yecora Rojo, and 58 to 75% increase in severity for Kern), which resulted in a significant decrease in yield (Yecora Rojo 12% decrease P = 0.047, Kern 21% decrease P = 0.006). These results suggest that the 7S chromosome segment carrying Lr47 has replaced a gene located in chromosome 7A in Yecora Rojo and Kern that has a positive effect on resistance to the predominant stripe rust races in California (e.g., PST100, PST101). Therefore, the T. speltoides segment including Lr47 would provide an advantage in areas under leaf rust infection but should be tested in other genetic background for its effect on stripe rust resistance.
No leaf rust was detected in the 2003 or 2004 field trials. However during the seed increases of these lines in 2002 at UC Davis we observed increased resistance to leaf rust in the Yecora Rojo Lr47 line (no infection) compared to the adjacent recurrent parent Yecora Rojo (80% infection, susceptible reaction). The recurrent parent Kern was resistant to these leaf rust races.
The two isogenic lines carrying the Lr47 gene showed a significantly higher (P = 0.002) grain protein content than the lines without the T. speltoides chromosome segment associated with the presence of the Lr47 chromosome segment in the two locations tested in 2004 (average increase of 530 g of protein per 100 kg of grain).
Isogenic Lines for Genes Lr37/Yr17/Sr38 from T. ventricosum
The Yr17, Lr37, and Sr38 rust resistance genes, which confer resistance in wheat against stripe rust, leaf rust, and stem rust respectively, were initially introgressed in the winter bread wheat ‘VPM1’ from T. ventricosum (Tausch.) Cess., Pass. & Gib. (Maia, 1967) and are located in a 2NS/2AS translocation (Bariana and McIntosh, 1993). Rust races with virulence to Yr17 and Lr37 have been identified in some countries, but this gene cluster still provides resistance to a wide range of races and is useful in combination with other rust resistance genes.
Characterization of the 2NS/2AS translocation with molecular markers indicated that the 2NS translocation replaced approximately half of the short arm of chromosome 2A (distal 25–38 cM). A PCR assay (Helguera et al., 2003) was used to introgress the 2NS chromosome segment from HRW ‘Madsen’ into HRS ‘Anza’ CItr15284 (Qualset et al., 1984). The BC6F4 seed of the Anza homozygous lines carrying the 2NS/2AS translocation was deposited at the National Small Grains Collection (NSGC) as Anza Lr37/Yr17/Sr38.
Isogenic lines were tested for leaf rust resistance at the Cereal Disease Laboratory (Helguera et al., 2003) and for stripe rust resistance in field trials at Davis (CA, 2004) and Kings (CA, 2004) using a split plot design with four replications (plot size 1.2 by 4.0 m at Davis and 1.5 by 4.0 m at Kings). The isogenic lines were morphologically similar and showed no significant differences in flowering time or height. The presence of the stripe rust resistance gene Yr17 significantly reduced the severity of the stripe rust infection from 60% to almost no infection (Davis P = 0.03, Kings P = 0.003). The recurrent parent Anza has the slow rusting complex Lr34/Yr18 (Mc Intosh et al., 1995) suggesting that the addition of Yr17 increased the slow rusting resistance to stripe rust provided by Yr18. The improved resistance of the Anza Lr37/Yr17/Sr38 line resulted in increased yields at both locations, but the differences were not significant (average increase 663 kg ha–1, Davis P = 0.07, Kings P = 0.17). The molecular and field data confirmed that the Lr37/Yr17/Sr38 resistance gene complex was successfully transferred to Anza.
Small quantities of seed of these germplasm lines may be obtained from the corresponding author for 5 yr. Recipients of seed are asked to make appropriate recognition of the source of the germplasm if it is used in the development of a new cultivar, germplasm, parental line, or genetic stock.
ACKNOWLEDGMENTS
This project was supported by the National Research Initiative of the USDA Cooperative State Research, Education and Extension Service (CSREES), grant numbers 2005-00975 and IFAFS 2001-04462.
NOTES
Accepted for publication June 30, 2005.
REFERENCES
This article has been cited by other articles:
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  J. C. Brevis, O. Chicaiza, I. A. Khan, L. Jackson, C. F. Morris, and J. Dubcovsky Agronomic and Quality Evaluation of Common Wheat Near-Isogenic Lines Carrying the Leaf Rust Resistance Gene Lr47 Crop Sci., July 1, 2008; 48(4): 1441 - 1451. [Abstract] [Full Text] [PDF]
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