Disease resistance. Leaf Rust Resistance.

Lr34 - Yr18

Contributed by Marcelo A. Soria, Wenjun Zhang and Jorge Dubcovsky

We also acknowledge valuable contributions by Harbans Bariana, Manilal William, Beat Keller, Evans Lagudah and Bob McIntosh.

Background information

More than 60 leaf rust resistance genes and QTLs have been described in wheat (1). Many of them are race-specific genes, and several are currently used by breeders to develop new cultivars. However, the resistance provided by these genes can be short-lived as new races of the leaf rust pathogen, Puccinia triticina, are continuously evolving and acquire virulence against these genes. In order to obtain cultivars with good levels of protection under high disease pressure, several ‘slow rusting” gene complexes need to be combined. Besides, the effect of slow rusting genes is more dependent on environmental conditions. Wheat breeders can use slow rusting genes as a complement to race-specific genes. The availability of molecular markers greatly facilitates the pyramidization process.

A small group of leaf rust resistance genes are known as "slow rusting genes", such as Lr34 (2) and Lr46 (3). They provide durable and non-specific adult plant resistance but their effect is more reduced than that of race-specific genes. Lr34 was recently cloned (11) and it was shown that it is the same gene as Yr18 (resistance to adult plant stripe rust), powdery mildew resistance (Pm38) and leaf tip necrosis (Ltn1). This gene codes for a putative ABC transporter. A similar tight linkage or pleiotropic effect was observed between Lr46 and Yr29, also a slow rusting gene for stripe rust.

Lr34 was first described in cultivar Frontana in 1966 (4). It is located on the short arm of chromosome 7D, close to locus Xgwm295. The resistance phenotype displayed by this gene includes longer latent period, fewer uredina and smaller uredina size. Lr34 is tightly linked to the leaf tip necrosis (LTN) locus, it is also possible that the LTN phenotype could be a pleiotropic effect of Lr34 itself (5).

Methods

For some CIMMYT germplasms the LTN phenotype can be used directly as a morphological marker (6). Lagudah et al (12) developed an STS marker, csLV34, that maps 0.4 cM from Lr34, and was validated in many lines and cultivars from different breeding programs worldwide (see the methods section for protocols). In the paper reporting the cloning of Lr34 (11), Krattinger et al. described several markers that differentiate among the loss-of-function alleles of Lr34.

Available germplasm

Lr34 is a gene present in many parent lines that have been used for breeding commercial varietes around the world. The STS marker csLV34 was proved an effective marker to differentiate between llines carrying Lr34 and its isogenic counterparts without the gene. Among others, csLV34 was validated in Thatcher, Glenlea, Jupateco R, Opata, Fukuho-komugi, Condor, Cook, Anza, Forno, Bezostaya, Otane and Chinese Spring.

Additional information. Field testing

Singh and Huerta Espino (8) analyzed different yield-related parameters in the Mexican spring cultivar Jupateco and a near isogenic line (NIL) derived from it and carrying Lr34 (Jutapeco-Lr34). They found that in disease-free environments Jupateco-Lr34 had significant, but generally small, reductions in biomass, grain per spike and grains/m². In some experiments they also observed negative effects of Lr34 on mean grain yield and mean grain weight. On the other hand, in leaf-rust affected plots Jutapeco showed significantly higher yield penalties than Jupateco-Lr34.

Labuschagne et al. (9) studied the effect of Lr34 on breadmaking quality in the South African cultivar Kareen. They compared Kareen with several different NILs derived from it and carrying Lr34. Kareen-Lr34 NILs had a flour protein content and water absorption values significantly higher than that of Kareen, while flour extraction and mixograph development time were similar. Only one Lr34-NIL showed a significantly lower SDS-sedimentation value. The authors concluded that Lr34 has an overall advantageous effect on breadmaking quality on this line.

References

1. Catalogue of gene symbols for wheat. McIntosh RA, Yamazaki Y, .Devos KM, Dubcovsky J, Rogers R, Appels R. In: KOMUGI, Integrated wheat Science Database [web link]

2. Effect of leaf rust resistance gene Lr34 on components of slow rusting at seven growth stages in wheat. Singh RP, Huerta-Espino J. In: Euphytica, 2003, 129:371-376. [abstract]

3. Characterization of Lr46, a gene conferring partial resistance to wheat leaf rust. Martínez F, Niks RE, Singh RP, Rubiales D. In: Hereditas, 2001, 135:111-114. [abstract]

4. Inheritance of adult-plant leaf rust resistance derived from the common wheat varieties Exchange and Frontana. Dyck PL, Samborski DJ, Anderson RG. In: Canadian Journal of Genetics and Cytology, 1966, 8:665-671.

5. Dissection of quantitative and durable leaf rust resistance in Swiss winter wheat reveals a major resistance QTL in the Lr34 chromosomal region. Schnurbusch T, Paillard S, Schori A, Messmer M, Schachermayr G, Winzeler M, Keller B. In: Theoretical and Applied Genetics, 2004, 108:477-484. [abstract]

6. Association between gene Lr34 for leaf rust resistance and leaf tip necrosis in wheat. Singh RP. In: Crop Science, 1992, 32: 874-878. [abstract]

7. Microsatellite markers for genes Lr34/Yr18 and other quantitative trait loci for leaf rust and stripe rust resistance in bread wheat. Suenaga K, Singh RP, Huerta-Espino J, William HM. In: Phytopathology, 2003, 93:881-890. [abstract]

8. Effect of leaf rust resistance gene Lr34 on grain yield and agronomic traits of spring wheat. Singh RP, Huerta-Espino J. In: Crop-Science, 1997, 37:390-395. [abstract]

9. The influence of leaf rust resistance genes Lr29, Lr34, Lr35 and Lr37 on breadmaking quality in wheat. Labuschagne MT, Pretorius ZA, Grobbelaar B. In: Euphytica,2002, 124: 65–70. [abstract]

10. Tagging and validation of a major quantitative trait locus for leaf rust resistance and leaf tip necrosis in winter wheat cultivar forno. Schnurbusch T, Bossolini E, Messmer B, Keller B.In: Phytopathology, 2004, 94: 1036-1041. [abstract]

11. A putative ABC transporter confers durable resistance to multiple fungal pathogens in wheat. Krattinger SG, Lagudah ES, Spielmeyer W, Singh RP, Huerta-Espino J,McFadden H, Bossolini E, Selter LL, Keller B. In: Science, 2009, 323:1360-1363. DOI: 10.1126/science.1166453.

12. Molecular genetic characterization of the Lr34/Yr18 slow rusting resistance gene region in wheat. Lagudah ES, McFadden H, Singh RP, Huerta-Espino J, Bariana HS, Spielmeyer W. In: TAG Theoretical and Applied Genetics, 2006, 114:21-30. DOI: 10.1007/s00122-006-0406-z.