Disease resistance. Leaf rust.

Lr46 - Yr29

References

1. Lr46: A Gene Conferring Slow-Rusting Resistance to Leaf Rust in Wheat. Singh RP, Mujeeb-Kazi A, Huerta-Espino J. In: Phytopathology, 1998, 88(9):890-894.

Wheat (Triticum aestivum) cultivar Pavon 76 carries slow-rusting resistance to leaf rust that has remained effective in Mexico since its release in 1976. 'Pavon 76' was crossed with two leaf rust-susceptible wheat cultivars, Jupateco 73S and Avocet S, and between 118 and 148 individual F₂ plant-derived F₃ and F₅ lines were evaluated for adult-plant leaf rust resistance at two field sites in Mexico during different seasons. Evaluation of F₁ plants and parents indicated that the slow-rusting resistance was partially dominant. Segregation in the F₃ and F₅ generations indicated that the resistance was based on two genes with additive effects. Monosomic analysis was carried out to determine the chromosomal locations of the resistance genes. For this purpose, two or three backcrossderived cytogenetic populations were developed by crossing 'Pavon 76' with a monosomic series of adult-plant leaf rust-susceptible cultivar Lalbahadur. Evaluation of such BC₂F₃ and BC₃F₃ lines from 16 confirmed 'Lalbahadur' monosomics indicated that one slow-rusting gene was located in chromosome 1B of 'Pavon 76'. This gene, designated as Lr46, is the second named gene involved in slow-rusting resistance to leaf rust in wheat.

2. 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.

Components of resistance conferred by the Lr46 gene, reported as causing "slow rusting" resistance to leaf rust in wheat, were studied and compared with the effects of Lr34 and genes for quantitative resistance in cv. Akabozu. Lr34 is a gene that confers non-hypersensitive type of resistance. The effect of Lr46 resembles that of Lr34 and other wheats reported with partial resistance. At macroscopic level, Lr46 produced a longer latency period than observed on the susceptible recurrent parent Lalbahadur, and a reduction of the infection frequency not associated with hypersensitivity. Microscopically, Lr46 increased the percentage of early aborted infection units not associated with host cell necrosis and decreased the colony size. The effect of Lr46 is comparable to that of Lr34 in adult plant stage, but in seedling stage its effect is weaker than that of Lr34.

3. Molecular Marker Mapping of Leaf Rust Resistance Gene Lr46 and Its Association with Stripe Rust Resistance Gene Yr29 in Wheat. William M, Singh RP, Huerta-Espino J, Ortiz Islas S, Hoisington D. In: Phytopathology, 2003, 93(2):153-159.

Leaf and stripe rusts, caused by Puccinia triticina and P. striiformis, respectively, are globally important fungal diseases of wheat that cause significant annual yield losses. A gene that confers slow rusting resistance to leaf rust, designated as Lr46, has recently been located on wheat chromosome 1B. The objectives of our study were to establish the precise genomic location of gene Lr46 using molecular approaches and to determine if there was an association of this locus with adult plant resistance to stripe rust. A population of 146 F₅ and F₆ lines produced from the cross of susceptible 'Avocet S' with resistant 'Pavon 76' was developed and classified for leaf rust and stripe rust severity for three seasons. Using patterns of segregation for the two diseases, we estimated that at least two genes with additive effects conferred resistance to leaf rust and three to four genes conferred resistance to stripe rust. Bulked segregant analysis and linkage mapping using amplified fragment length polymorphisms with the 'Avocet' × 'Pavon 76' population, F₃ progeny lines of a single chromosome recombinant line population from the cross 'Lalbahadur' × 'Lalbahadur (Pavon 1B)', and the International Triticeae Mapping Initiative population established the genomic location of Lr46 at the distal end of the long arm of wheat chromosome 1B. A gene that is closely linked to Lr46 and confers moderate levels of adult plant resistance to stripe rust is identified and designated as Yr29.

4. 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(7):881-890.

Leaf rust and stripe rust, caused by Puccinia triticina and P. striiformis, respectively, are important diseases of wheat in many countries. In this study we sought to identify molecular markers for adult plant resistance genes that could aid in incorporating such durable resistance into wheat. We used a doubled haploid population from a Japanese cv. Fukuho-komugi × Israeli wheat Oligoculm cross that had segregated for resistance to leaf rust and stripe rust in field trials. Joint and/or single year analyses by composite interval mapping identified two quantitative trait loci (QTL) that reduced leaf rust severity and up to 11 and 7 QTLs that might have influenced stripe rust severity and infection type, respectively. Four common QTLs reduced stripe rust severity and infection type. Except for a QTL on chromosome 7DS, no common QTL for leaf rust and stripe rust was detected. QTL-7DS derived from 'Fukuhokomugi' had the largest effect on both leaf rust and stripe rust severities, possibly due to linked resistance genes Lr34/Yr18. The microsatellite locus Xgwm295.1, located almost at the peak of the likelihood ratio contours for both leaf and stripe rust severity, was closest to Lr34/Yr18. QTLs located on 1BL for leaf rust severity and 3BS for stripe rust infection type were derived from 'Oligoculm' and considered to be due to genes Lr46 and Yr30, respectively. Most of the remaining QTLs for stripe rust severity or infection type had smaller effects. Our results indicate there is significant diversity for genes that have minor effects on stripe rust resistance, and that successful detection of these QTLs by molecular markers should be helpful both for characterizing wheat genotypes effectively and combining such resistance genes.