A prebreeding study of introgression spring bread wheat lines carrying combinations of stem rust resistance genes, Sr22+Sr25 and Sr35+Sr25

The Sr22, Sr35, and Sr25 genes attract the attention of bread wheat breeders with their effectiveness against Puccinia graminis f. sp. tritici race Ug99 and its biotypes. The effectiveness and impact of Sr22+Sr25 and Sr35+Sr25 gene combinations on agronomic traits have not yet been studied. In the present article, these traits were studied using the spring bread wheat lines L503/W3534//L503, L503/Sr35//L503/3/L503 carrying the Sr22+Sr25 and Sr35+Sr25 genes during 2016–2020. These lines were assessed for resistance to P. graminis f. sp. tritici under natural epiphytotics and to the Saratov, Lysogorsk and Omsk populations of the pathogen and to the PgtZ1 (TKSTF) and PgtF18.6 fungus isolates in laboratory conditions (TKSTF + Sr33). The presence of the studied Sr-genes was confirmed by using molecular markers. Prebreeding studies were conducted during 2018–2020 vegetation periods. Under the natural epiphytotics of the pathogen and in the laboratory conditions, the Sr22+Sr25 combination was highly effective, while Sr35+Sr25 was ineffective. For grain yield, the lines with the Sr22+Sr25 and Sr35+Sr25 genes were superior to the recipient cultivar L503 in one year (Sr22+Sr25 in 2019; Sr35+Sr25 in 2018), with a decrease in 2020, but in general there were no differences. For the period 2018–2020, both combinations showed a decrease in 1000 grains weight and an increase in the germination-earing period. The line with Sr22+Sr25 genes showed insignificant effects on gluten and dough tenacity, but the ratio of dough tenacity to extensibility was higher, and flour strength, porosity and bread volume were lower; in the line with Sr35+Sr25 genes, the gluten content was lower, but the strength, tenacity of the dough and the ratio of dough tenacity to extensibility were higher, flour strength and the porosity of the bread were at the recipient level, but the volume of bread was lower.

Assessment of Genetic Diversity for Stem Rust and Stripe Rust Resistance in an International Wheat Nursery Using Phenotypic and Molecular Technologies

The objective of this study was to assess diversity for stem rust and stripe rust resistance in an international wheat screening nursery under greenhouse conditions using pathotypes with known avirulence/ virulence profiles. A set of 95 entries of an international wheat screening nursery collected from material generated by staff of the International Maize and Wheat Improvement Centre (CIMMYT) was tested against seven Australian Pgt and five Pst pathotypes through artificial inoculation under the greenhouse conditions using standard procedures. Ten all-stage stem rust resistance genes (Sr8a, Sr8b, Sr9b, Sr12, Sr17, Sr23, Sr24, Sr30, Sr31 and Sr38) and seven all-stage stripe rust resistance genes (Yr3, Yr4, Yr6, Yr9, Yr17, Yr27 and Yr34) were postulated either singly or in combinations based on seedling responses of test entries against pathotypes differing in virulence for commonly deployed genes. Sr30 and Sr38 were the most common stem rust resistance genes in this nursery. The Sr38-linked stripe rust resistance gene Yr17 was present in high proportion. The presence of rust resistance genes Sr24, Sr31/Yr9, Sr38/Yr17 and Yr4 were confirmed using the closely linked molecular markers. The adult plant resistance (APR) genes Sr2 and Lr34/Yr18/Sr57 were detected using linked molecular markers csSr2 and csLV34, respectively. Genotypes carrying combinations of stem rust and stripe rust resistance were identified for use as donor sources in breeding programs.

Advances in identifying stripe rust resistance genes in cereals

Stripe rust is one of the most serious wheat diseases of the world, usually resulting in massive loss of grain production. The most effective and environmentally friendly way to control the spread of stripe rust is to plant wheat varieties that carry stripe rust resistance genes. The identification and utilization of stripe rust resistance genes is very important for achieving this goal. This chapter summarizes the hazards of stripe rust and the current progress in the discovery of stripe rust resistance genes. It also introduces the advanced methods to identify Yr genes. The chapter also shows the successful application of Yr genes in wheat breeding program in southwestern China, which is the largest epidemic area of stripe rust in the world. The further identification and applications of Yr genes are also discussed.

Evaluation of Wheat Germplasm for Resistance to Leaf Rust (Puccinia triticina) and Identification of the Sources of Lr Resistance Genes Using Molecular Markers

Leaf rust, caused by Puccinia triticina (Ptr), is a significant disease of spring wheat spread in Kazakhstan. The development of resistant cultivars importantly requires the effective use of leaf rust resistance genes. This study aims to: (i) determine variation in Ptr population using races from the East Kazakhstan, Akmola, and Almaty regions of Kazakhstan; (ii) examine resistance during seedling and adult plant stages; and (iii) identify the sources of Lr resistance genes among the spring wheat collection using molecular markers. Analysis of a mixed population of Ptr identified 25 distinct pathotypes. Analysis of these pathotypes using 16 Thatcher lines that are near-isogenic for leaf rust resistance genes (Lr) showed different virulence patterns, ranging from least virulent “CJF/B” and “JCL/G” to highly virulent “TKT/Q”. Most of the pathotypes were avirulent to Lr9, Lr19, Lr24, and Lr25 and virulent to Lr1, Lr2a, Lr3ka, Lr11, and Lr30. The Ptr population in Kazakhstan is diverse, as indicated by the range of virulence observed in five different races analyzed in this study. The number of genotypes showed high levels of seedling resistance to each of the five Ptr races, thus confirming genotypic diversity. Two genotypes, Stepnaya 62 and Omskaya 37, were highly resistant to almost all five tested Ptr pathotypes. Stepnaya 62, Omskaya 37, Avangard, Kazakhstanskaya rannespelaya, and Kazakhstanskaya 25 were identified as the most stable genotypes for seedling resistance. However, most of the varieties from Kazakhstan were susceptible in the seedling stage. Molecular screening of these genotypes showed contrasting differences in the genes frequencies. Among the 30 entries, 22 carried leaf rust resistance gene Lr1, and two had Lr9 and Lr68. Lr10 and Lr28 were found in three and four cultivars, respectively. Lr19 was detected in Omskaya 37. Two single cultivars separately carried Lr26 and Lr34, while Lr37 was not detected in any genotypes within this study. Field evaluation demonstrated that the most frequent Lr1 gene is ineffective. Kazakhstanskaya 19 and Omskaya 37 had the highest number of resistance genes: three and four Lr genes, respectively. Two gene combinations (Lr1, Lr68) were detected in Erythrospermum 35 and Astana. The result obtained may assist breeders in incorporating effective Lr genes into new cultivars and developing cultivars resistant to leaf rust.

Comparison of productivity elements of recombinants of spring bread wheat with translocation from Thinopyrum elongatum carrying rust resistance genes

There have been presented the results of a comparative estimation of recombinants developed on the basis of two commercial varieties (‘Sibirskaya 17’ and ‘Novosibirskaya 31’) hybridized with ‘Thatcher Lr19’ and ‘Thatcher Lr24’. Recombinants were evaluated in the field conditions in 2016, 2017 and 2020. The purpose of the current study was to identify the effect of translocations from Thinopyrum elongatum on the manifestation of productivity elements in recombinants of spring bread wheat developed on the basis of two commercial varieties. The analysis of the genetic composition of the Puccinia triticina populations in Western and Eastern Siberia did not identify genes which were virulent to resistance genes Lr19, Lr24, Lr28, Lr41, Lr47, Lr45 LrSp, Lr6Agi 1 and Lr6Agi 2. The recombinants developed on the basis of the variety ‘Sibirskaya 17’ (the variety productivity was 398.3 g/m2 , grain weight per head was 1.35 g, 1000-grain weight was 37.8 g) were characterized by the severity of the main agronomically valuable traits at the level of the recipient variety, or significantly lower (productivity was 271.5–327.8 g/m2 , grain weight per head was 1.03–1.16 g, 1000-grain weight was 32.5–36.4 g). The recombinants carrying translocations (the length of the period ‘sprouts-heading’ was 44.4 and 44.5 days, grain weight per head was 1.20 and 1.24 g) developed on the basis of the variety ‘Novosibirskaya 31’ (with 42.4 days, 1.02 g) have demonstrated a significant increase in the length of the period ‘sprouts-heading’ and grain weight per head in comparison with the recombinants without translocations (41.6 and 43.6 days, 0.99 and 1.10 g). On average over 3 years, 12 recombinants hybridized from the combination ‘Novosibirskaya 31 x Thatcher Lr19’ produced higher yields (355.6–427.5 g/m2) than those of the recipient variety (301.5 g/m2), both with (6 pcs.), and without (6 pcs.) a translocation.