Intrachromosomal mapping of genes for dwarfing (Rht12) and vernalization response (Vrn1) in wheat by using RFLP and microsatellite markers

For intrachromosomal mapping of the dominant GA-sensitive dwarfing gene Rht12 and the vernalization response gene Vrn1 on chromosome 5 A, an F₂ population was established using a wide (synthetic) wheat cross. In addition to restriction fragment length polymorphism (RFLP) probes four microsatellite markers were incorporated. Rht12 was mapped distally to four RFLP loci (Xmwg616, Xpsr164, Xwg114, Xpsr1201) and three microsatellite markers (Xgwm179, Xgwm410, Xgwm291), known to be located on the segment of chromosome SAL which was ancestrally translocated and is homoeologous to Triticeae 4 L. The map position of Rht12 suggests that it is homoeologous to the dominant GA-sensitive dwarfing gene Ddw1, present on chromosome 5RL. The vernalization response gene Vrn1 showed linkage to Xwg644, as might be expected from comparative maps.     

Wheat leaf rust resistance gene Lr59 derived from Aegilops peregrina

An Aegilops peregrina (Hackel in J. Fraser) Maire & Weiller accession that showed resistance to mixed leaf rust ( Puccinia triticina Eriks.) inoculum was crossed with, and backcrossed to, hexaploid wheat ( Triticum aestivum L.). During backcrossing a chromosome segment containing a leaf rust resistance gene (here designated Lr59 ) was spontaneously translocated to wheat chromosome 1A. Meiotic, monosomic and microsatellite analyses suggested that the translocated segment replaced most of, or the complete, 1AL arm, and probably resulted from centromeric breaks and fusion. The translocation, of which hexaploid wheat line 0306 is the appropriate source material, provided seedling leaf rust resistance against a wide range of South African and Canadian pathotypes.     

Mapping of Lr56 translocation recombinants in wheat

In an attempt to transfer the Lr56/Yr38 resistance loci from Aegilops sharonensis to wheat, a 6A‐6S^sh chromosome translocation was produced. It involves essentially the entire chromosome 6S^sh with a small terminal segment of 6AL. Induced homoeologous recombination of the translocated chromosome with 6A produced numerous recombinants including three recombined chromosomes carrying Lr56 that could not be precisely mapped for lack of suitable markers. This study aimed to determine the chromosomal locations of the translocation breakpoints in these three recombinants using various DNA markers as well as physical and genetic mapping. The three recombinants Lr56‐39, ‐157 and ‐175 carry small segments of Ae. sharonensis chromatin distally to the Xgpw4329 and IWA5416 loci near the 6AS telomere. The Ae. sharonensis chromatin that remains in each line includes a homoeolocus of the wheat marker locus Xdupw217 (on 6BS) and its characteristic amplification product can be used as a dominant marker for the presence of Lr56. Of the three recombined chromosomes, Lr56‐157 retained the least alien chromatin and appears to be the best candidate for use in wheat breeding.     

Cytogenetical studies in wheat XVI. Chromosome location of a new gene for resistance to leaf rust in a Japanese wheat-rye translocation line

Summary A leaf rust resistant wheat-rye translocation stock, ST-1, introduced from Japan, comprised distinct morphological types. One type possessed a T1BL·1RS chromosome with genes Lr26, Yr9 and Sr31. A second type carried a new gene, Lr45, located in a large segment of rye chromosome translocated to wheat chromosome 2A. Its structure was identified as T2AS-2RS·2RL. Despite the homoeology of the 2A and 2R chromosomes and the high level of compensation provided by the translocation, Lr45 was not normally inherited and is probably associated with agronomic deficiencies that will prevent its exploitation in agriculture.Contribution No. 94-509-J from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan, USA.     

Mapping of powdery mildew and leaf rust resistance genes on the wheat-rye translocated chromosome T1BL·1RS using molecular and biochemical markers

Powdery mildew and leaf rust resistance genes on the 1RS arm of the T1BL·1RS translocated chromosome were mapped in relation to the Sec‐1 locus and AFLP and restriction fragment length polymorphism markers, respectively, employing segregating F₃ populations. Integration of molecular markers indicated that Pm17 lies between the Lr26 and Sec‐1 loci, with both resistance genes allocated distally to the Sec‐1 locus in the satellite of the 1RS arm.     

28个小麦微核心种质抗叶锈性分析

选取在成株期表现高、中、低抗叶锈的28个小麦微核心种质,利用39个以Thatcher为背景的近等基因系(或单基因系)作为已知基因的鉴别寄主,接种8个小麦叶锈菌致病型进行苗期抗叶锈基因推导,结合成株期抗病鉴定,初步明确了这些品种(系)的抗性和可能携带的抗病基因。利用19个与Lr基因紧密连锁或共分离的分子标记,对28个微核心种质进行抗叶锈病基因的进一步鉴定,推测新克旱9号可能含有Lr17、Lr2b、Lr14a和Lr33;兴义4号可能含有Lr26、Lr36和Lr37;紫皮可能含有Lr2b和Lr34;大白皮含有Lr1;毕红穗含有Lr1、Lr10和Lr34;中优9507含有Lr10;小白麦、红粒当年老、老麦、蝉不吱、苏麦3号和车锏子含有Lr1和Lr34;红花早可能含有Lr1、Lr34、Lr14a和Lr2b;江西早、泡子麦、三月黄、有芒扫谷旦、阜阳红、成都光头和酱麦可能含有Lr34;敦化春麦和甘肃96可能含有Lr28;欧柔可能含有Lr34、Lr16、Lr11、Lr3bg和Lr33;此外,新克旱9号、兴义4号、红花早、红粒当年老、欧柔、有芒扫谷旦、成都光头、甘肃96、小红皮、定兴寨、中优9507和红冬麦中可能含有未知抗病基因;在这28份种质中,不含Lr9、Lr19、Lr20、Lr21、Lr24、Lr29、Lr35、Lr38和Lr47基因。研究结果表明,测试的微核心种质中含有比较丰富的抗叶锈病基因,可为育种提供丰富的抗源。     

土耳其8个小麦品种农艺性状及抗叶锈性分析

为确定8个来自土耳其的普通小麦品种在我国的应用前景,对其进行全生育期农艺性状观察,并利用44个以Thatcher为背景的近等基因系(单基因系)作为已知基因的鉴别寄主,接种8个小麦叶锈菌致病型进行苗期抗叶锈基因推导,结合成株期抗病鉴定,初步明确了这些品种(系)的抗性和可能携带的抗病基因。利用20个与Lr基因紧密连锁或共分离的分子标记,对8个土耳其小麦品种进行抗叶锈病基因的进一步鉴定。推测YJ000900中可能含有Lr1、Lr3、Lr17、Lr20;YJ000906中可能含有Lr1、Lr17、Lr20;YJ000901、YJ000902、YJ000904、YJ000905、YJ000907中可能含有Lr1;8个材料中均不含Lr9、Lr19、Lr20、Lr21、Lr24、Lr26、Lr28、Lr29、Lr34、Lr35、Lr37、Lr38和Lr47基因。结果表明,来自土耳其的8个小麦材料具有较差的抗叶锈性、抗寒和抗倒伏能力,而且产量低,不适宜于大规模推广种植,也不能作为我国小麦抗叶锈的抗源使用。     

Evaluation and reduction of Lr19-149, a recombined form of the Lr19 translocation of wheat

The Lr19 translocation was introgressed from Thinopyrum ponticum in 1966. It has not been used in wheat breeding in many countries despite it being an excellent source of leaf rust resistance as it carries an undesirable gene(s) coding for yellow endosperm pigmentation. A shortened form, Lr19-149, was since produced and lacks the yellow pigment genes. A yield trial with near isogenic lines of both the original and shortened translocations suggested that Lr19 may cause a small reduction in kernel size and anincrease in loaf volume, effects which are not associated with Lr19-149. In Lr19-149 heterozygotes the translocation generally showed reduced pollen transmission whereas its transmission through egg cells was mostly normal. An attempt to shorten Lr19-149 through allosyndetic recombination in the absence of Ph1b produced four recombinants which were characterized by means of RFLP and AFLP polymorphisms and physically mapped with a set of 27 deletion lines. In three recombinants (252, 299 and 462) Thinopyrum chromatin proximally to Lr19 was exchanged for wheat chromatin. In one recombinant (478) chromatin distally from Lr19 was replaced. Based on physical map distance estimates it appears that the Lr19 translocation in the shortest recombinant (299) may have been reduced to about one third or less of its original size. It may now be possible to obtain a further, albeit relatively small, decrease in the size of the translocation through homologous crossover between recombinants 299 and 478. Similar to Lr19-149, the new recombinants show self elimination in heterozygotes and they have apparently retained the Sd2 locus. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mapping quantitative trait loci in wheat for resistance against greenbug and Russian wheat aphid

Breeding for genetic resistance against greenbug and Russian wheat aphid (RWA) is the most effective way of controlling these widespread pests in wheat. Earlier work had shown that chromosome 7D of a synthetic hexaploid wheat, ‘Synthetic’ (T. dicoccoides × Ae. squarrosa) (AABB × DD) gave resistance when transferred into the genetic background of an aphid‐susceptible cultivar, ‘Chinese Spring’, as the recipient. To map the genes involved, a set of 103 doubled haploid recombinant substitution lines was obtained from crossing the 7D substitution line with the recipient, and used to determine the number and chromosomal location of quantitative trait loci (QTL) controlling antixenosis and antibiosis types of resistance. Antixenosis to RWA was significantly associated with marker loci Xpsr687 on 7DS, and Xgwm437 on 7DL. Antibiosis to greenbug was associated with marker loci Xpsr490, Rc3 (on 7DS), Xgwm44, Xgwm111, Xgwm437, Xgwm121 and D67 (on 7DL). Similarly, antibiosis to RWA was linked to loci Xpsr490, Rc3, Xgwm44, Xgwm437 and Xgwm121. At least two QTL in repulsion phase, one close to the centromere either on the 7DS or 7DL arms, and a second distal on 7DL could explain antibiosis to RWA and, partially, this mechanism against greenbug.     

SCAR marker tagged to the alien leaf rust resistance gene Lr19 uniquely marking the Agropyron elongatum-derived gene Lr24 in wheat: a revision

A sequence characterized amplified region (SCAR) marker tagged to an Agropyron elongatum‐derived leaf rust resistance (Lr) gene Lr19 was validated on 18 known alien Lr gener in near‐isogenic lines (NILs) in the variety ‘Thatcher’, along with three wheat cultivers carrying Lr24 and two carrying Lr19. The marker was expressed only in the Lr24 lines confirming that the marker tagged the geneLr24. The monomorphic expression of the SCAR marker in 10NIL pairs for Lr19 and Lr24 revealed that each NIL pair possessed the same gene, Lr24. The donor parents used in the NIL pairs for Lr19 (‘Sunstar*6/C80‐1′) and Lr24 (‘TR380‐14*7/3Ag#14′) amplified the same fragment. Nonsegregation for leaf rust in the F₂ population of the cross between the above donor parents confirmed the presence of the same gene in the two parents. Apparently, a genuine parent stock of ‘Sunstar*6/C80‐1’ was not involved in the development of the NIL pairs for Lr19 due to an improper maintence bredding protocol either at source or destination which went undetected in the absence of signs of virulence for either gene in the region.     

Endopeptidase polymorphism and linkage of the Ep-D1c null allele with the Lrl9 leaf-rust-resistance gene in hexaploid wheat

The aim of this study was to test whether the null allele Ep-D1c of the endopeptidase Ep-D1 can be used as a marker for the Lrl9 leaf rust resistance gene. The frequency of Ep-D1c was determined in 1134 winter wheat, spring wheat and spelt breeding lines and varieties. Only eight lines were found to carry Ep-D1c. Six of these lines originated from crosses with RL6040, the gene donor for Lrl9. The other two lines were leaf-rust susceptible in the seedling stage and therefore did not carry Lr19. The genetic distance between Ep-D1c and Lr19 was determined in a reciprocal cross between the lines FAP75184 (Ep-D1c, Lr19) and FAP75106 (Ep-D1a, leaf-rust susceptible in the seedling stage). Out of 840 F₂ seedlings screened, 162 were homozygous for Ep-D1c. From 150 of these F₂ plants, F₃ seedlings were screened for segregation for leaf-rust resistance with isolates avirulent on Lr19. Only one F₂ plant produced susceptible F₃ progeny indicating a recombination event between Ep-D1c and Lr19. From these data, a genetic distance of 0.33 ± 0.33cM between Ep-D1c and Lr19 was calculated. The results show that Ep-D1c is a useful marker for a practical breeding programme allowing the rapid identification of plants homozygous for Lrl9.     

Identification of a molecular marker linked to an Agropyron elongatum-derived gene Lr19 for leaf rust resistance in wheat

The leaf rust resistance gene Lr19, transferred from Agropyron elongatum into wheat (Triticum aestivum L.) imparts resistance to all pathotypes of leaf rust (Puccinia recondita f.sp. tritici) in South‐east Asia. A segregating F₂ population from a cross between the leaf rust resistant parent ‘HW 2046’ carrying Lr19 and a susceptible parent ‘Agra Local’ was screened in the phytotron against a virulent pathotype 77‐5 of leaf rust with the objective of identifying the molecular markers linked to Lr19. The gene was first tagged with a randomly amplified polymorphic DNA (RAPD) marker S73₇₂₈. The RAPD marker linked to the gene Lr19 which mapped at 6.4 ± 0.035 cM distance, was converted to a sequence characterized amplified region (SCAR) marker. The SCAR marker (SCS73₇₁₉) was specific to Lr19 and was not amplified in the near‐isogenic lines (NILs) carrying other equally effective alien genes Lr9, Lr28 and Lr32 enabling breeders to pyramid Lr19 with these genes.     

Genetics of leaf rust resistance in three Americano landrace-derived wheat cultivars from Uruguay

A genetic analysis of the landrace‐derived wheat accessions Americano 25e, Americano 26n, and Americano 44d, from Uruguay was conducted to identify the leaf rust resistance genes present in these early wheat cultivars. The three cultivars were crossed with the leaf rust susceptible cultivar ‘Thatcher’ and approximately 80 backcross (BC1) F₂ families were derived for each cross. The BC1F₂ families and selected BC1F₄ lines were tested for seedling and adult plant leaf rust resistance with selected isolates of leaf rust, Puccinia triticina. The segregation and infection type data indicated that Americano 25e had seedling resistance genes Lr3, Lr16, an additional unidentified seedling gene, and one adult plant resistance gene that was neither Lr12 nor Lr13, and did not phenotypically resemble Lr34. Americano 26n was postulated to have genes Lr11, Lr12, Lr13, and Lr14a. Americano 44d appeared to have two possibly unique adult plant leaf rust resistance genes.     

Evaluation of seedling and adult plant resistance to leaf rust in European wheat cultivars

Summary A set of 105 European wheat cultivars, comprising 68 cultivars with known seedling resistance genes and 37 cultivars that had not been tested previously, was tested for resistance to selected Australian pathotypes of P. triticina in seedling greenhouse tests and adult plant field tests. Only 4% of the cultivars were susceptible at all growth stages. Twelve cultivars lacked detectable seedling resistance to leaf rust, and among the remaining cultivars, 10 designated genes were present either singly or in combination. Lr13 was the most frequently detected gene, present in 67 cultivars, followed by the rye-derived gene Lr26, present in 19 cultivars. Other genes present were Lr1, Lr3a, Lr3ka, Lr10, Lr14a, Lr17b, Lr20 and Lr37. There was evidence for unidentified seedling resistance in addition to known resistance genes in 11 cultivars. Field tests with known pathotypes of P. triticina demonstrated that 57% of the cultivars carried adult plant resistance (APR) to P. triticina. The genetic identity of the APR is largely unknown. Genetic studies on selected cultivars with unidentified seedling resistances as well as all of those identified to carry APR are required to determine the number and inheritance of the genes involved, to determine their relationships with previously designated rust resistance genes, and to assess their potential value in breeding for resistance to leaf rust.     

Characterization of wheat-alien translocations conferring resistance to diseases and pests: current status

Summary Wild relatives of common wheat, Triticum aestivum, and related species are an important source of disease and pest resistance and several useful traits have been transferred from these species to wheat. C-banding and in situ hybridization analyses are powerful cytological techniques allowing the detection of alien chromatin in wheat. C-banding permits identification of the wheat and alien chromosomes involved in wheat-alien translocations, whereas genomic in situ hybridization analysis allows determination of their size and breakpoint positions. The present review summarizes the available data on wheat-alien transfers conferring resistance to diseases and pests. Ten of the 57 spontaneous and induced wheat-alien translocations were identified as whole arm translocations with the breakpoints within the centromeric regions. The majority of transfers (45) were identified as terminal translocations with distal alien segments translocated to wheat chromosome arms. Only two intercalary wheat-alien transloctions were identified, one induced by radiation treatment with a small segment of rye chromosome 6RL (H25) inserted into the long arm of wheat chromosome 4A, and the other probably induced by homoeologous recombination with a segment derived from the long arm of a group 7 Agropyron elongatum chromosome with Lr19 inserted into the long arm of 7D. The presented information should be useful for further directed chromosome engineering aimed at producing superior germplasm.Contribution No. 96-55-J from the Kansas Experimental Station, Kansas State University, Manhattan, KS 66506-5502, USA.     

Resistance to leaf rust in cultivars of bread wheat and durum wheat grown in Spain

A set of bread wheat and durum wheat cultivars adapted to Spanish conditions was tested for resistance against leaf rust caused by different pathotypes of Puccinia triticina in field trials and in growth chamber studies. Lower levels of resistance were found in durum wheat than in bread wheat. The most frequent Lr genes found in bread wheat were Lr1, Lr10, Lr13, Lr20, Lr26 and Lr28. In durum wheat, additional resistance genes that differed from the known Lr genes were identified. The level of partial resistance to leaf rust was in general low, although significant levels were identified in some bread wheat and durum wheat cultivars.     

Physiological basis of yield gains in wheat associated with the LR19 translocation from Agropyron elongatum

The physiological and genetic basis of yield improvement in wheat isonly partially understood. Nonetheless, a significant increase in yield andbiomass has been observed in several backgrounds when alien chromatinassociated with Lr19 was introgressed from Agropyronelongatum. Theoretically, higher yield and biomass may be achievedthrough (i) greater interception of incident radiation, (ii) increasedradiation use efficiency, (iii) a more optimal source-sink balance permittinghigher sink demand and/or a higher partitioning of assimilates to yield. Theobjectives of the current study were to evaluate the performance of nearisogenic lines differing in Lr19 to observe the physiological basis ofsuperior performance. Lr19 was associated with increases in yield(average 13%), final biomass (10%) and grain number (15%) in allbackgrounds studied. Differences were not associated with improved lightinterception based on measurements of biomass shortly after canopyclosure, nor with improved radiation use efficiency (RUE) prior to grainfilling based on biomass accumulation rate and direct measurement offlag-leaf photosynthetic rate prior to anthesis. Lr19 was associatedwith an increased partitioning of biomass to spike growth at anthesis(13%), a higher grain number per spike, and higher RUE and flag-leafphotosynthetic rate during grain filling. The mechanism causing increasedpartitioning of assimilates to spikes relative to the rest of the plant in Lr19 isolines was apparently not related to phenology or assimilationcapacity.     

First report of leaf rust pathotypes virulent to highly effective Lr-genes transferred from Agropyron species to bread wheat

The gene pool of effective sources of leaf rust resistance used in the breeding of wheat (Triticum aestivum L.) includes several species of the genus Agropyron. The genes deriving therefrom (Lr 19, 19d, 29, Agⁱ1, Agⁱ2, 38) are highly effective to pathotypes of Puccinia recondita Rob. ex Desm. In the Saratov and Orenbhurg districts of Russia, however, pathotypes virulent to these genes have been discovered. These pathotypes are virulent to Saratov-bred cultivars carrying Lr 19, to ‘Indis’ (Lr 19d) and RL 6097 (Lr 38). The distribution of virulence on the ‘Thatcher’ near-isogenic lines with different Lr genes shows that most of the Lr genes tested are susceptible to these new pathotypes of P. recondita, but the Lr genes Lr 9, 23, 24, 26 were exceptions. The inoculation of Mexican bread wheat cultivars, which carry widespread Lr gene combinations, by these pathotypes disclosed different infection types. Out of 10 Lr-gene combinations, four were highly effective; namely the combinations Lr 13 + 26, Lr 26 +?, Lr 23+26 and Lr 23+26+34.     

Characterization of stem rust resistant derivatives of wheat cultivar Amigo

Summary Originally developed for resistance to greenbug derived from Insave rye, Amigo wheat carries two genes for resistance to stem rust. One of these genes is associated with a rye chromosome 1RS segment carrying the Sec-1 protein marker and presumably greenbug resistance. The second gene which is genetically linked to leaf rust resistance is associated with an Agropyron-derived segment. Rust tests in Canada confirmed that these genes were Sr24 and Lr24. In contrast to Agent and certain 3D/Ag derivatives from Dr. E.R. Sears, the Amigo source of Sr24/Lr24 freely recombined with white seed colour during backcrossing.     

56个小麦品种（系）的苗期和成株抗叶锈鉴定

为了研究中国小麦品种中所携带的抗叶锈基因,对56个小麦品种（系）进行苗期接种推导其中所含有的抗叶锈基因,同时连续2年对供试材料进行田间成株抗叶锈鉴定。通过苗期基因推导结合分子标记辅助检测,结果表明,在36个小麦品种中共鉴定出Lr26、Lr34、Lr1、Lr2a、Lr11、Lr20、Lr30、Lr33和Lr44等9个抗叶锈基因,其中28个品种含有Lr26,Lr1和Lr20分别存在于6个品种中,4个品种含有Lr30,Lr11和Lr44各存在于2个品种中,Lr2a、Lr33和Lr34各自在1个品种中出现。经过2年的田间抗叶锈鉴定共筛选出46个慢锈品种。筛选到的这些苗期和成株抗病品种均可用于小麦持久抗叶锈品种的培育。