Transgressive segregation for resistance to yellow rust in wheat

Summary Crosses were made between wheat varieties Joss Cambier, Nord Desprez and Maris Bilbo, all classified as susceptible to yellow rust in field tests, and between Cappelle Desprez and Maris Huntsman, both classified as moderately and durably resistant. Selection for resistance to yellow rust among the progeny was carried out using races of Puccinia striiformis able to overcome all the known race-specific components of resistance in both parents of each cross. Lines with greater resistance than in both parents were obtained from each cross, those with greatest resistance being obtained from the cross between the moderately resistant parents. Three lines selected for resistance from the cross of Joss Cambier with Nord Desprez and one from the cross of Cappelle Desprez with Maris Huntsman, together with the parents, were tested in the field with 12 races of P. striiformis. Nord Desprez possessed a previously undetected race-specific component. The selected lines also displayed race-specific resistance, some of which was clearly related to race-specificity of the parents, and a component of resistance, greater than in both parents, that was effective against all 12 races. The possible origin and potential durability of this transgressive level of resistance is discussed. It is suggested that such transgressive resistance is more likely to be durable if it is derived from parents that have shown durable resistance.     

Characterization of the durable resistance to yellow rust in old winter wheat cultivars in the Netherlands

Summary Winter wheat cultivars released in the Netherlands before 1930 carried durable resistance to yellow rust. Cultivars released in the period between 1930 and 1950 often were durably resistant while recent cultivars infrequently showed durable resistance. This durable resistance was not difficult to transfer to new cultivars. Twenty nine older cultivars with durable resistance and eight recent non-durably resistant cultivars were tested in the seedling stage and in the adult plant stage against 12 West-European yellow rust races and against some non-European races in the seedling stage only. The adult plant tests were carried out in race nursery tests in the Flevopolder. Per race nursery all 37 cultivars, planted in hills of about 20 plants on both sides of the highly susceptible cv. Michigan Amber, were exposed to one race.The infection type of each cultivar-race combination was scored on 0 to 9 scale once in the seedling stage and twice in the adult plant stage. In the race nurseries the percentage leaf area affected was evaluated three times to be used to calculate the area under the disease progress curve (AUDPC). This AUDPC multiplied with the mean infection type in the field gave the susceptibility index (SI).The infection types were classified into resistant (R), intermediate (I) or susceptible (S) when the infection types were 0 to 3, 4 to 6 or 7 to 9, respectively. Four categories of resistance were discerned on the basis of the three infection type scores: 1) RRR, overall resistance; complete or near-complete resistant at all stages. 2) SRR, adult plant resistance, complete- or near-complete resistant at the adult plant stage only. 3) SRS and SSR, temperature sensitive resistance, the resistance changed from the one evaluation data to the other. 4) SSS and an SI lower than that of Michigan Amber, partial resistance.The frequencies of overall, adult plant and temperature sensitive resistance were 1.4, 52 and 54% in the older cultivars and 40, 62 and 22% in the recent ones, respectively. Among the older cultivars all had a fair to high level of partial resistance, the SI being on average only 20% of that of Michigan Amber, while most cultivars also seemed to carry temperature sensitive resistance. The partial resistance of the recent cultivars was of a much lower level with a mean SI compared to that of Michigan Amber of 61%. Partial resistance was highly correlated (r = –0.94) with the mean resistance scores from the Dutch Recommended Cultivars Lists. It was concluded that partial resistance and temperature sensitive resistance were the major components of the durable resistance in the older cultivars.     

Genes for resistance to stripe rust in four spring wheat varieties

Summary Four spring wheat (Triticum aestivum L.) varieties differing in origin and reaction in the seedling stage to pathotype CDL-6 (extant in California) were intercrossed and examined in greenhouse conditions in F₁, F₂, and F₃ generations. Digenic and transgressive segregation was found in all crosses. The four varieties each had infection types (1 immune, 9 susceptible) and putative resistance genes as follows: Anza, IT 7, YrA; Glennson 81, IT 2, Yr9; Yecora Rojo, IT 6, YrC; and Ollanta, IT 4–6, YrL. Anza was classified as susceptible, Yecora Rojo and Ollanta as intermediate in seedling resistance, and Glennson 81 as resistant in the seedling stage.     

A recessive resistance gene for yellow rust (Puccinia striiformis West.) in bread wheat (Triticum aestivum L.)

Summary Three lines derived from the old dirty Dutch land variety Gelderse Ris were resistant against race 66(70)EO(16) of yellow rust. It was found that this resistance was conditioned by one recessive gene provisionally coded yrGR.     

Does interplot interference affect the screening of wheat for yellow rust resistance?

Summary In small plots, adjacent to one another, a representational error can be expected when screening for quantitative forms of resistance to airborne pathogens. The representational error or interplot interference may occur as an underestimation of the level of resistance and/or as an error in the ranking of the entries tested.Four experiments were carried out with wheat (Triticum aestivum) exposed to yellow rust (Puccinia striiformis), three in Kenya, one in Mexico (exp. III).In experiment I 57 entries were compared in an unreplicated trial with three adjacent and one isolated plot situation. The range in the standard deviation of and the ranking order for disease severity (DS) between the 57 entries were the same for all plot situations at all observation dates.In experiment II nine entries from experiment I, representing a wide range of quantitative resistance and having a similar heading date, were compared in adjacent plots consisting of two rows of 10 m in eight replicates and isolated plots of one, six and ten rows of 4 m in three replicates. The range in the standard deviation of and the ranking order for DS between the entries were very similar for the four plot situations.The 10 entries in experiment III differed from those in experiment II, but represented a similar wide range of resistance. Three adjacent plot situations of 0.9×0.5 m, 0.9×2.0 m and 2.7×2.0 m, respectively, were compared with one isolated one with plots of 2.7×2.0 m. The ranking order was not affected, the range in and the standard deviation of the DS in the isolated plots were slightly larger than in the adjacent plots.In experiment IV two mixtures of two entries each were made. Per mixture one entry was fairly resistant (R) the other rather susceptible (S). Within each mixture the entries had a similar heading date. The ratios of the R:S mixtures were 0:100, 50:50, 67:33, 75:25, 82:18 and 100:0. The DS of each entry was the same as its DS in monoculture irrespective of the mixture ratio. There was no mixture effect on DS.The three experiments in Kenya gave no indication of any interplot interference occurring. In Mexico there was a very slight underestimation of the resistance in adjacent plots. The ranking order was always the same irrespective of the test plot situation. The screening of wheat for yellow rust resistance in small adjacent plots is representative for the farmers fields. This is contrary to what has been found in other windborne pathosystems such as barley-barley leaf rust (strong under estimation of resistance), barley-powdery mildew (some under estimation of resistance and different ranking order) and durum wheat-stem rust (fair under estimation of resistance).     

Virulence of wheat yellow rust races and resistance genes of wheat cultivars in Ecuador

Virulence factors of the yellow rust, Puccinia striiformis, populations in bread wheat were studied in Ecuador between 1973 and 2004. The number of virulence factors has increased markedly from very few in the early seventies to 16 at the end of the 90s. Isolates belonging to race 0E0 seem to be the ancestor of a rapid virulence evolution of yellow rust in Ecuador. This evolution can be explained by a single step mutation pattern. Virulence to the resistance genes Yr1, Yr2, Yr2+, Yr3V, Yr3ND, Yr4+, Yr6, Yr6+, Yr7, Yr7+, Yr9, Yr9+, Yr11, Yr12, Yr18, Yr24, Yr26 and those in the cultivars Carstens V (YrCV) Strubes Dickkopf (YrSD), Suwon92/Omar (YrSU), Spaldings Prolific (YrSP), Anza (YrA+) and Selkirk (YrSK). was identified. Virulence to Yr5, Yr8, Yr10, and Yr15 was not found. Postulation of resistance genes at the seedling stage of 14 Ecuadorian wheat cultivars indicated that these cultivars carry alone or in combinations the resistance factors Yr1, Yr2, Yr3, Yr6, Yr9 and/or other undesignated resistance factors. Yellow rust evolution in Ecuador has been associated with deployment of these resistance genes. None of these deployed Yr resistance genes are effective to the present yellow rust population in Ecuador.     

Postulation of resistance genes to yellow rust in wild emmer wheat derivatives and advanced wheat lines from Nepal

Summary Seedlings of 38 wild emmer derivatives, and a total of 53 advanced wheat varieties/lines introduced from the International Maize and Wheat Improvement Centre (CIMMYT) or other sources, Nepalese breeding lines and local cultivars were inoculated with 18 different yellow rust isolates to postulate yellow rust resistance genes (Yr). Many wild emmer wheat derivatives used were resistant to all isolates indicating the presence of undescribed genes. Some derivatives carried Yr9, Yr6 and/or YrSU. Genes Yr1, Yr2, Yr6, Yr7, Yr8, Yr15, YrSU and YrA+ are no longer effective in Nepal; Yr4, Yr5, Yr9, Yr10, YrSP and YrSD are still effective; the effectiveness of Yr3 remains unclear. This study shows that stripe rust resistance in seedling stage of most Nepalese cultivars and advanced materials is based on Yr9 with combinations of Yr2, Yr6, Yr7, and YrA+, of which only Yr9 is still effective in Nepal. In many countries Yr9 has lost its effectiveness. Therefore the introduction of new Yr-genes from wild emmer wheat in Nepalese cultivars is highly important.     

Resistance in spelt wheat to yellow rust

Summary Seven spelt wheat accessions of different origin were hybridized with the susceptible bread wheat cultivar Taichung 29 in order to study the genetics of their resistance to yellow rust (Puccinia striiformis Westend. f. sp. tritici). One Iranian and five European accessions were found to carry Yr5 of Triticum aestivum ssp. spelta var. album, whereas a factor for resistance in the Iranian accession 415 was confirmed to be genetically distinct from Yr5. The alleles for resistance in each of the accessions studied showed a monogenic dominant mode of inheritance. Twenty-eight spelt wheat accessions, including those studied for their resistance to yellow rust, were subjected to polyacrylamide-gel-electrophoresis to study variation for gliadin storage protein patterns. Thirteen distinct patterns were revealed, implying the presence of duplicates within the studied spelt wheat collection.     

Genes for resistance to stripe rust in four spring wheat varieties

Summary The stripe rust resistant spring wheat (Triticum aestivum L.) varieties Anza, Glennson 81, Ollanta, and Yecora Rojo gave 1,2,2, and 2-gene segregations, respectively, in hybrids with susceptible Jupateco 73 when inoculated in field conditions at Davis, California USA with Puccinia striiformis West. pathotype CDL-6 and rated at post-heading stage. Intercrosses of these varieties, Anza/Yecora Rojo was not studied, permitted the following conclusions about the genes expressed in adult plants: Anza, one recessive gene; Glennson 81, two dominant genes; Ollanta, two genes, at least one is dominant; and Yecora Rojo; one dominant and one recessive gene, one of which is common with Ollanta. The resistance genes in these varieties, which expressed resistance in the seedling stage, were believed to be effective at the adult stage. Thus, seven resistance genes were identified in the four varieties. The genotypes were designated for the purposes of this study as follows: Anza, YrA YrH; Glennson 81, Yr9, YrJ, Ollanta YrL YrD; and Yecora Rojo, YrC YrD. It was recommended that these and other Yr genes be used as multiple gene complexes to increase durability of resistance to P. striiformis, an organism known to evolve virulence rapidly in field conditions. The demonstrated durability of Anza in California may be a result of its combination of resistance alleles at two loci.     

An analysis of genes for resistance against Indian stem rust races in two bread wheat cultivars

Summary The genetic constitution of two bread wheat accessions from the International Spring Wheat Rust Nurseries (E 5883 and E 6032) has been studied for reaction to four Indian races of stem rust. Analysis of E 5883 has revealed that for each of the races 15C, 21 and 40 a single dominant gene operates for resistance. The dominant gene against race 15C was identified as Sr6. The dominant genes for resistance against races 21 and 40 were found to be different from the genes described so far. Resistance against race 122 is controlled by a single recessive gene producing characteristically a 2 type of reaction. This gene was identified as Sr8.The resistance of E 6032 against each of the races 15C, 21 and 40 is controlled by two genes, one dominant and one recessive, which act independently. Dominant genes effective against 15C, 21 and 40 were conclusively identified as Sr6, Sr5 and Sr9b, respectively. From the correlated behaviour against races 15C and 40 as well as from the phenotypes of the resistance reactions rhe same recessive gene, undescribed so far, operates against the two races. The second recessive gene operating against race 21 was also observed to be different from those so far designated. E 6032 was, however, found to be susceptible to races 122.The presence of Sr6 both in E 5883 and E 6032 against race 15C was further confirmed through F₂ and F₃ segregation data.     

The inheritance of stem rust and leaf rust resistance in some Ethiopian wheat collections

Summary Common and durum wheat populations obtained from Sweden and originally collected in Ethiopia were screened for resistance to steum rust and leaf rust. Resistant selections of common wheat were crossed and backcrossed with either stem rust susceptible RL6071, or leaf rust susceptible Thatcher. Genetic studies, based largely on tests of backcross F₂ families, showed that four of the selections had in common a recessive gene SrA. Plants with this gene were resistant (1⁺ infection type) to all stem rust races tested. This gene was neither Sr26 nor Sr29. The resistance of other selections, based on tests with an array of rust isolates, was due to various combinations of Sr6, 8a, 9a, 9d, 9c, 11, 13, 30, and 36. One of the selections had linked genes, Lr19/Sr25. Another selection had a dominant gene for resistance (;1 infection type) to all the races of leaf rust. With the possible exception of this gene for leaf rust resistance and SrA, no obviously new resistance was found.     

Monosomic analyses of stripe rust and leaf rust resistance genes in winter wheat varieties Lüquyu and Yantar

Summary A set of 21 monosomics of Novosadska Rana-1 was used to locate the rust resistance genes of Lüqiyu, a stripe rust resistant line developed by BAU and Yantar, a leaf rust resistant wheat introduced from Bulgaria. The resistance of the former to p. striiformis race C25 was conditioned by a dominant gene located on chromosome 2B, whereas that of the latter to P. recondita race CL3 was controlled by two complementary dominant genes located on chromosomes 5A and 1D, respectively. The relationship of the stripe rust resistance gene in Lüqiyu to Yr5, Yr7 or Yr _Suwon' all located on chromosome 2B is unknown. The two complementary leaf rust resistance factors in Yantar appear to be new.     

Enhanced leaf rust resistance in wheat conditioned by resistance gene pairs with Lr13

Summary Leaf rust resistance gene Lr13 is present in many North American hard red spring wheat cultivars that have shown durable resistance to leaf rust. Fifteen pair-wise combinations of Lr13 and seedling leaf rust resistance genes were developed by intercrossing near isogenic Thatcher lines. In both seedling and adult plant tests, homozygous paired combinations of specific resistance genes with Lr13 had enhanced resistance relative to either parent to rust isolates that had intermediate avirulent infection types to the additional genes. In field tests, homozygous lines were more resistant than either parent if the additional leaf rust gene conditioned an effective level of resistance when present singly.     

Effectiveness of genes for leaf rust resistance in international wheat rust nurseries, 1970–1975

Monogenic lines resistant to leaf rust of spring and winter wheats were grown in the world wheat-producing areas from 1970 through 1975. Lines containing the alleles Lr9 (Wi), Lr9 (Tc), and Lr19 (Tc) were more resistant to the leaf rust pathogen than those containing Lr1 (Tc), –1 (Wi), –1,3 (Wi), –2A (Tc), –2A (Wi), –2D (Tc), –3 (Tc), –3 (Wi), –10 (Tc), –16 (Tc), –17 (Tc), –18 (Tc), or –2D (Pld). Monogenic line Lr1 (Wi) possibly has more than one gene for resistance and resistance properties similar to cultivars with field resistance. A computer data base was created to produce the information used in this paper.Formerly Research Agronomist, Field Crops Laboratory, now Supervisoty Computer Specialist, DSAD; and Research Plant Pathologist, Germplasm Resources Laboratory, ARS, BARC-West, Beltsville, Maryland 20705.     

The role of Lr34 in imparting durable resistance to wheat leaf rust through gene interaction

Summary The leaf rust responses of wheat lines carrying the complementary genes Lr27 and Lr31 and the same genes in a Chinese Spring background which contains Lr34, indicate that Lr34 interacts with the complementary genes to give enhanced levels of field resistance to leaf rust. Lr34, particularly in combination with other genes, is considered to be an important gene for imparting a high degree of durable resistance to leaf rust. Its similarity to Sr2, an adult plant gene for resistance to stem rust and its association with adult plant resistances to stem and stripe rusts are discussed.     

Variation of characters in near-isogenic lines of wheat with added genes for leaf rust resistance

Summary Using the cultivar Arina as the recurrent parent, six backcrosses were made with two donor lines carrying the leaf rust resistance genes Lr1 and Lr9, respectively. Selection for leaf rust resistance occurred at the seedling stage in the greenhouse; the first plants transferred to the field were BC₆F₄s. Frequency distribution of the 332 Lr1/7 × Arina and the 335 Lr9/7 × Arina lines showed continuous variation for yellow rust resistance and heading date in these leaf rust near-isogenic lines (NILs). Similar results were also obtained for plant height, for resistance to powdery mildew and glume blotch, as well as for baking quality characters in another set of more advanced NILs. The available information on the behaviour of one of the parents of cultivar Arina led to the conclusion that the expressed yellow rust resistance is quantitative and might possibly be durable.     

Genetics of leaf rust resistance in 13 accessions of the Watkins wheat collection

Summary The inheritance of leaf rust resistance was studied in 13 accessions of the A.E. Watkins wheat collection. Eight of the accessions (V409, V624, V628, V712, V731, V734, V745, and V855) were shown to have gene Lr33 and four of these (V409, V624, V628, and V731) also have LrW. Accessions V624 and V338 have LrB, and V377 and V488 have Lr11. V46 has an unidentified gene that gives an intermediate level of resistance. V860 has a partially dominant gene that gives a fleck reaction to avirulent isolates in the seedling stage. This gene is different from LrW and may be previously unidentified. It has been assigned the temporary gene symbol LrW2. In addition to seedling-effective genes, V46, V731, and V745 may have Lr34 and V745 may have Lr13. The adult-plant resistance in V488, V624, and V860 could not be identified. Seedling gene LrW2 and some of the adult-plant resistance should be useful sources of resistance.Contribution NO. 1576.     

A test of supposed mutants for stem rust resistance in wheat

Summary Eight stem rust (Puccinia graminis tritici Eriks. and Henn.) resistant lines (designated TICENA lines) that had been selected by Veiga et al. (1981) following gamma radiation of BH-1146 wheat (Triticum aestivum L.) were studied. Six of the lines were resistant to race 15B-1 of stem rust and susceptible to race 56, and proved to carry the gene Sr7a. TICENA 4 carries two unidentified genes, each giving resistance to one of the two races. TICENA 10 carries Sr6, Sr7a and an unidentified gene giving resistance to race 56 but not 15B-1. The results raise doubts about the supposed origin of the lines as mutants.     

Genetic and environmental variability in wheat characteristics reported to be involved in morphological resistance to wheat stem rust

Summary Four morphological characteristics of wheat peduncles were evaluated for genetic and environmental variability. The thickness of the epidermis and the amount and distribution of chlorenchyma tissue in the peduncle were measured. The genetic variability was estimated to be large, whereas the environmental variability was small. It was also concluded that cultivars could be screened for morphological characteristics of the peduncle that contributed to non-specific resistance to stem rust with a minimum sample size of about 10 plants per replication from a single location.Paper No 9328, Scientific Journal Series, Minnesota Agricultural Experiment Station. University of Minnesota. St. Paul. MN 55108.     

Identification and cataloguing of genetic information for resistance to wheat leaf rust

Summary Specific host-pathogen relationship is used to derive genetic information for resistance in commercial cultivars. Twenty-two cultivars were classified into 12 groups based on their reactions to 13 leaf rust (Puccinia recondita) races of India. The cultivars in each group were matched with the Lr gene carrying lines to see which genes they might possess. Confirmation of this information was sought through pedigree analyses.(1) Agra local and NP4 do not seem to have any resistance genes. (2) C306 has gene Lr14a, and NP824 one of the genes Lr12, Lr13, Lr14a or Lr22. (3) kalyansona carries Lr13 and another additional gene not in study. (4) Chhoti Lerma, NP852, Pusa Lerma, Sharbati Sonora, Shera, UP301 form one group and carry Lr1. (5) Sonalika seems to have Lr2a, Lr11 and additional genes. (6) Hy.65 has Lr10. (7) HS1076-2 and HW135 have the genes Lr2a and Lr3do. (8) HW124 carries the genes Lr1 and Lr3do. (9) Safed Lerma has Lr1 and Lr17. (10) NP846 has the genes Lr1 and Lr15. (11) HB117-107, Janak, UP215 form one group and possess the genes Lr3do and Lr15. (12) Girija possesses the genes Lr10 and Lr15.Based on such grouping of commercial cultivars for resistance genes a Catalogue system is advocated for the design of wheat breeding programmes like the development of multiline and multigene cultivars.