Inheritance of the Powdery Mildew Resistance Gene Pm9 in Relation to Pm1 and Pm2 of Wheat

The inheritance of the powdery mildew resistance gene Pm9 originating from the hexaploid spring wheat cultivar ‘Normandie’ was analyzed in relation to Pm1 and Pm2. Two leaf segments of individual P_1?, P_2?, F_1? and F₂-plants of the cross ‘Normandie’ (Pm1, 2, 9) בFederation’ (no known Pm gene) were inoculated separately with two powdery mildew isolates. Using powdery mildew isolate No. 6 virulent for Pm1 and Pm2 but avirulent for Pm9, a 1 resistant (r): 3 susceptible (s) F₂-segregation was found for the Pm9 gene. Using powdery mildew isolate No. 3 virulent for Pm1 and Pm9 but avirulent for Pm2, a 3 (r): 1 (s) F₂-segregation was found for the Pm2 gene. Combining the data of both experiments (leaf segments of identical plants had been used), a 9 (sr): 3 (ss): 3 (rr): 1 (rs) segregation resulted for the F₂ of this cross: therefore, independent inheritance of the genes Pm2 and Pm9 can be concluded. Similarly, the cross ‘Mephisto’ (Pm1, 2, 9) בAmor’ (no known Pm gene) was analyzed. The Pm9 gene again showed a monogenically recessive inheritance, whereas Pm1 showed a monogenically intermediate segregation upon inoculation with powdery mildew isolate No. 9a virulent for Pm2 and Pm9 but avirulent for Pm1. Combining the single gene segregations, linkage between both genes was found among the progenies. A distance of 8.5 cM was calculated. Analyzing a set of spring wheat cultivars with seven defined powdery mildew isolates, the presence of Pm1, Pm2 and Pm9 in these lines was verified; in most cases, Pm1 occurred together with Pm9.     

Inheritance of the Powdery Mildew Resistance Mlk in Wheat

The inheritance of the Mlk powdery mildew resistance originating from ‘Heine 2174.50’ was analyzed by crossing the Mlk resistant cultivar ‘Ralle’× cv. ‘Amor’ (highly susceptible) and vice versa and by observing the reactions of F₁- and F₂-plants after inoculation with two different Mlk avirulent powdery mildew isolates. In all cases, a 3 (resistant): I (susceptible) segregation was found in F₂. The reactions of the F₂plants against the two powdery mildew isolates were identical in each case. Therefore, it is supposed that one dominant resistant gene is responsible for the resistant reactions against these two isolates. These results support the earlier assumption of Heun and Fischbeck (1987b) that the whole Mlk resistance pattern is controlled by a single gene.     

Lack of durability of resistance to cereal rusts in wheat when selection is for complete resistance

Twenty-one bread-wheat entries were selected after careful screening for complete or near-complete resistance to yellow rust (Puccinia striiformis), stem rust (P. graminis), and leaf rust (P. recondita). In 1987, the 21 entries were intercrossed in a near-half diallel scheme. The resulting 190 F₂ populations were advanced to F₇ under selection for complete resistance to the three rusts and for good agronomic types. In 1992 the 21 parents and 140 selected F₇ lines were assessed for their resistance to the three rusts. Of the 21 parents, 12 showed a breakdown of yellow rust resistance, five a breakdown of stem rust resistance and two a breakdown of leaf rust resistance. In addition, several of the 140 selected F₇ lines, all still resistant in F₆, had become susceptible to one or more of the rusts. It appears that a progression towards more complex races, especially of yellow rust, is inevitable for the wheat-cereal rust patho-systems when the selection is for complete or near-complete resistance.     

Cytogenetical studies in wheat. XVIII. Gene Yr24 for resistance to stripe rust

A new gene, Yr24, for resistance to stripe rust was transferred from a durum accession to common wheat via an amphiploid (synthetic wheat) with Aegilops tauschii. Yr24 was located in chromosome 1B by monosomic analysis. Its genetic linkage of 4 cM with Yr15 indicated its localization to the short arm.     

Relationship between the Origin of European Landraces and the Level of Partial Resistance to Wheat Leaf Rust

The reaction to leaf rust of 33 European spring-wheat landrace selections was assessed in the field and in the greenhouse to study the relationship between levels of partial resistance and levels of leaf rust at the origin of the landrace selections. The selections were classified into three groups according to the mean annual damage observed at the collection site. For each group of selections with high-infection types the mean disease-severity, area under disease progress curve and latency period were assessed. The data suggest that there is a greater likelihood of finding partial resistance in selections that come from locations with a high or intermediate mean annual damage as they displayed lower disease severity, lower area according to a disease-progress curve and a longer latency period than the selections from locations with low mean annual damage.     

Leaf rust and stripe rust resistance genes Lr54 and Yr37 transferred to wheat from Aegilops kotschyi

The tendency of unpaired meiotic chromosomes to undergo centric misdivision was exploited to translocate leaf rust and stripe rust resistance genes from an Aegilops kotschyi addition chromosome to a group 2 chromosome of wheat. Monosomic and telosomic analyses showed that the translocation occurred to wheat chromosome arm 2DL. The introgressed region did not pair with the corresponding wheat 2DL telosome during meiosis suggesting that a whole arm may have been transferred. Female transmission of the resistance was about 55% whereas male transmission was strongly preferential (96%). The symbols Lr54 and Yr37 are proposed to designate the new resistance genes.     

Assessment of partial resistance to powdery mildew in Chinese wheat varieties

Field trials in two cropping seasons and two locations in central China were conducted on 60 Chinese autumn‐sown wheat varieties to assess their partial resistance to powdery mildew. Mean levels of disease severity ranged from close to 0 to more than 90%. The method of inoculation and the location in which trials were conducted affected the relative performance of the varieties, but these effects were much smaller than the main effect of variety. The area under the disease progress curve was highly correlated with final disease severity, but both were poorly correlated with apparent infection rate. Disease severity was regressed against frequencies of virulence in the Blumeria graminis (syn. Erysiphe graminis) f sp. tritici populations in the trial plots. A vertical distance (D) from the mean mildew severity to the fitted line was calculated for each variety and was used to quantify partial resistance. Five of the 60 varieties, ‘Hx8541’, ‘E28547’, ‘Chuan1066’, ‘Zhe88pin6’ and ‘Lin5064’, consistently expressed relatively low levels of disease despite high frequencies of virulence in the pathogen and had consistently high D‐values. They may therefore have good levels of partial resistance.     

Sources of seedling and adult plant resistance to Puccinia striiformis f.sp. tritici in European wheats

One-hundred-and-forty-one wheat cultivars were tested at the seedling stage using up to 16 yellow rust isolates of diverse origin. Sixty-five resistance spectra were observed, including 20 spectra defined by differential cultivars with specific genes for resistance to Puccinia striiformis f.sp. tritici . Yr1 , Yr2 , Yr3 , Yr4 , Yr6 , Yr9 , Yr15 , Yr17 , Yr25 , Yr32 , and several additional sources of resistance were recognized. The resistance spectra were often conferred by Yr -genes and resistance factors with an unresolved genetic basis. All cultivars carried resistance and 27 had resistance for which no fully compatible isolate was detected. Yr15 was detected in four cultivars, a resistance from wild Emmer not previously reported in commercial wheat. There was no indication of Yr5 , Yr7 , Yr8 , Yr10 and Yr24 in any cultivar. Most cultivars were also investigated in field nurseries using up to nine isolates of Danish origin. Fifty-six cultivars displayed high or very high levels of resistance to any isolate in the field, and 18 of these showed full compatibility at the seedling stage to at least one isolate, i.e. revealing components of adult plant resistance.     

Chromosomal locations in common wheat of three new leaf rust resistance genes from Triticum monococcum

Monosomic analysis was conducted to determine chromosomal locations of three new leaf rust resistance genes recently transferred to common wheat (Triticum aestivum) from T. monococcum. The resistance gene in wheat germplasm line KS92WGRC23 was transferred from T. monococcum ssp. monococcum. The resistance genes found in KS93U3 and KS96WGRC34 were transferred from T. monococcum ssp. aegilopoides. Allelism tests showed that the three resistance genes were unlinked. The three lines were crossed with each of the seven A-genome Wichita monosomic lines. The leaf rust resistance genes in KS92WGRC23, KS93U3, and KS96WGRC34 were located on chromosomes 6A, 1A, and 5A, respectively, by monosomic analysis. These results demonstrate that the three new genes derived from T. monococcum are each different. They also differ from previously reported Lr genes. This information on chromosome location and the development of mapping populations will facilitate molecular tagging of the new genes. This revised version was published online in July 2006 with corrections to the Cover Date.     

The inheritance and expression of leaf chlorosis associated with gene Sr2 for adult plant resistance to wheat stem rust

Sr2, an important source of durable resistance to the wheat stem rust pathogen, is linked with a distinctive seedling chlorosis gene sc. The expression of sc is sensitive to temperature and light. The chlorosis can be induced by inoculation with the stem rust or leaf rust pathogens and also develops on uninfected leaves of rusted plants. This chlorosis is an excellent marker for Sr2 which previously was best monitored by the appearance of pseudo-black chaff on glumes or upper stem or the expression of resistance. However, the latter are only detected late in the season on field-grown adult plants. Chlorosis was recessive in F1 hybrids, however, it segregated in a dominant manner in some F3 lines presumably due to the presence of modifying genes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetics of multiple disease resistance in a doubled-haploid population of barley

The barley accession Q21861 possesses resistance to the stem-rust (Puccinia graminis f.sp. tritici), leaf-rust (P. hordei), and powdery-mildew (Blumeria graminis f.sp. hordei) pathogens. An anther-culture-derived doubled-haploid population was produced from F₁ plants from a cross of this accession and the susceptible breeding line SM89010 as a means of rapidly and efficiently determining the genetics of multiple disease resistance. The doubled-haploid population segregated 1:1 (resistant:susceptible) for resistance to the stem rust pathotype QCC indicating the involvement of a single resistance gene, rpg4. Two-gene (3:1) and one-gene (1:1) segregation ratios were observed for resistance to the stem-rust pathotype MCC at low (23–25°c) and high (27–29°C) temperature, respectively. These different segregation patterns were due to a pathotype × temperature interaction exhibited by rpg4 and Rpg1. another stem-rust-resistance gene present in Q21861. One-gene and two-gene segregation ratios were observed in reaction to the leaf rust and powdery mildew pathogens. These data demonstrate the utility of doubled haploid populations for determining the genetics of multiple disease resistance in barley.     

Genetic analysis of powdery-mildew resistance of a winter-wheat line, RE714, and identification of a new specific-resistance gene

The winter-wheat line RE714, resulting from an intergeneric cross between Aegilops squarrosa and Triticum dicoccum, and implying a sister line of ‘Roazon’ (VM4) in its genealogy, was obtained in order to increase the genetic diversity for disease resistance. The aim of this study was to identify and characterize the powdery-mildew-resistance gene(s) present in this line at the seedling stage on detached leaves. The comparison of the reaction of the RE714 line and of differential hosts to 24 Erysiphe graminis. f.sp. tritici isolates indicated that only Pm4a, Pm4b and/or Mlar genes could be present and that a new resistance factor, different from all known mildew-resistance genes, was present in this line. The powdery-mildew reactions of segregating F₂ populations produced evidence that RE714 carries the Pm4b allelic form and a recessive new resistance gene, tentatively designated mlre. While Ae. squarrosa was resistant to most isolates, T. dicoccum was specifically attacked by REV 14-virulent isolates and was therefore assumed to be the donor of mire. The VM4 parent was confirmed as the Pm4b donor.     

The linkage between the stem rust resistance gene Sr2 and pseudo-black chaff in wheat can be broken

Recessively inherited gene Sr2 has provided the basis of durable resistance to stem rust (caused by Puccinia graminis tritici) in wheat (Triticum aestivum L.) worldwide. The associated earhead and stem melanism or ‘pseudo‐black chaff’ is generally used as a marker for this gene. Sr2 has been postulated in many wheat cultivars of India including ‘Lok 1’, based on associated pseudo‐black chaff in adult plants, and leaf chlorosis in seedlings. However, dominant inheritance of the resistance factor operating in ‘Lok 1’, and a 13 : 3 (resistant : susceptible) F₂ segregation in the ‘Sr2‐line’ (‘Chinese Spring’⁶ × ‘Hope’ 3B) × ‘Lok 1’ cross confirmed that Sr2 was absent in ‘Lok 1’. Susceptible plants with a pseudo‐black chaff phenotype were observed in F₂ populations of ‘Agra Local’ (susceptible) × ‘Lok 1’, and the ‘Sr2‐line’ × ‘Lok 1’ crosses. Most of the F₃ families derived from the susceptible F₂ segregants with pseudo‐black chaff phenotypes were true breeding for the expression of pseudo‐black chaff with susceptibility to stem rust. Thus, linkage of pseudo‐black chaff with Sr2 in wheat can be broken, and hence, caution may be exercised in using pseudo‐black chaff as a marker for selecting Sr2 in breeding programmes.     

小麦白粉菌寄主范围研究初报

人工接种及田间调查的结果表明，采自河南和陕西的小麦白粉菌系能正常地侵染７属２３种禾本科植物。其中有６属１１种禾草为国内首次报道的该菌寄主。连同前人的研究，目前发现的我国小麦白偻菌寄主植物已达１０属３１种。从小麦属各植物材料对小麦白粉菌的感染情况，进一步支持了小麦属的现代分类理论。     

Identification of Wheat Powdery Mildew Resistance Genes by Analysing Host-Pathogen Interactions

Fifty-nine winter wheat cultivars and thirteen lines possessing known powdery mildew resistance genes were inoculated with eleven different isolates. By comparing their resistance patterns the responsible major resistance genes of the above-mentioned cultivars have been determined. The so-called “Blaukorn” resistance is conditioned by gent Pm4b. The resistance patterns of Ml-i and Pm5 being similar, the relationship between them has to be analysed by segregating populations.     

Genes for wheat stem rust resistance postulated in German cultivars and their efficacy in seedling and adult‐plant field tests

Stem rust of wheat (caused by Puccinia graminis f.sp. tritici) gained high international attention in the last two decades, but does not occur regularly in Germany. Motivated by a regional epidemic in 2013, we analysed 15 spring and 82 winter wheat cultivars registered in Germany for their resistance to stem rust at the seedling stage and tested 79 of these winter wheat cultivars at the adult‐plant stage. A total of five seedling stem rust resistance genes were postulated: Sr38 occurred most frequently (n = 29), followed by Sr31 (n = 11) and Sr24 (n = 8). Sr7a and Sr8a occurred only in two spring wheat genotypes each. Four cultivars had effective seedling resistance to all races evaluated that could only be explained by postulating additional resistance genes (‘Hyland’, ‘Pilgrim PZO’, ‘Tybalt’) or unidentified gene(s) (‘Memory’). The three winter wheat cultivars (‘Hyland’ ‘Memory’ and ‘Pilgrim PZO’) were also highly resistant at the adult‐plant stage; ‘Tybalt’ was not tested. Resistance genes Sr24 and Sr31 highly protected winter wheat cultivars from stem rust at the adult‐plant stage in the field. Disease responses of cultivars carrying Sr38 varied. Mean field stem rust severity of cultivars without postulated seedling resistance genes ranged from 2.71% to 41.51%, nine of which were significantly less diseased than the most susceptible cultivar. This suggests adult‐plant resistance to stem rust may be present in German wheat cultivars.     

Cytogenetic studies in wheat XIX. Chromosome location and linkage studies of a gene for leaf rust resistance in the Australian cultivar 'Harrier'

Monosomic analysis indicated that a seedling leaf rust resistance gene present in the Australian wheat cultivar ‘Harrier’(tentatively designated LrH) is located on chromosome 2A. LrH segregated independently of the stripe rust resistance gene Yr1 located in the long arm of that chromosome, but failed to recombine with Lr17 located in the short arm. LrH was therefore designated Lr17b and the allele formerly known as Lr17 was redesignated as Lr17a. The genes Lr17b and Lr37 showed close repulsion linkage. Tests of allelism indicated that Lr1 7b is also present in the English wheats ‘Dwarf A’(‘Hobbit Sib’), ‘Maris Fundin’ and ‘Norman’. Virulence for Lr17b occurs in Australia, and pathogenicity studies have also demonstrated virulence in many western European isolates of the leaf rust pathogen. Despite this, it is possible that the gene may be of value in some regions if used in combination with other leaf rust resistance genes.     

Identification of specific powdery-mildew-resistance genes in individual wheat plants using the first two seedling leaves

Identification of resistance genes in individual plants requires the use of leaves that have homogeneous reactions to the pathogen. The reactions of the first two leaves of seedlings of 12 wheat differential varieties to 20 Erysiphe graminis f.sp. tritici isolates were compared using in vitro tests on detached leaf segments. The expression of resistance and susceptibility did not differ significantly between the first two leaves with the 12 resistance genes tested. Consequently, the identification of specific powdery-mildew-resistance genes in individual plants is possible if approximately 10 segments of the primary and secondary leaves are used, each of them inoculated by one out of a set of 10 differential isolates. The reaction pattern of a plant to the tester isolates is interpreted according to a procedure in two steps, that are easily computerized. Identification of resistance genes in individual plants is particularly useful for resistance studies in heterogeneous plant populations.     

Chromosomal location of powdery mildew resistance gene Pm16 in wheat using SSR marker analysis

The use of resistant cultivars is a most economical way to control powdery mildew (Blumeria graminis f.sp. tritici) in wheat (Triticum aestivum L.). Identification of molecular markers closely linked to resistance genes can greatly increase the efficiency of pyramiding resistance genes in wheat cultivars. The objective of this study was to identify molecular markers closely linked lo the powdery mildew resistance gene Pm16. An F₂ population with 156 progeny was produced from the cross‘Chancellor’(susceptible) ב70281’ (resistant), A total of 45 SSR markers on chromosomes 4A and 5B of wheat and 15 SSRs on chromosome 3 of rice was used lo lest the parents, as well as the resistant and susceptible bulks: the resulting polymorphic markers were used to genotype the F₂ progeny. Results indicated that the SSR marker Xgwm159, located on the short arm of chromosome 5B, is closely linked to Pm16 (genetic distance: 5.3 CM). The cytogenetical data presented in an original report, in combination with this molecular analysis, suggests that Pm16 may he located on a translocated 4A.5BS chromosome.