Stripe rust analysis of D-genome synthetic wheats (2n = 6x = 42, AABBDD) and their molecular diversity

Stripe or yellow rust caused by Puccinia striiformis f. sp. tritici is a threat to many of the existing cultivars of Pakistan. Many attempts are being made to evolve new varieties resistant to stripe rust to reduce the losses caused by this disease. For this purpose, novel genes are needed to incorporate into the existing cultivars. These genes are found in the wild progenitors of wheat that are D-genome donors to wheat. As a result of extensive research, wheat synthetic hexaploids have been developed. These synthetics have resistances against biotic as well as abiotic stresses including the yellow rust. A group of such synthetics has been identified which seems resistant to this destructive disease. This group was tested under field conditions to identify resistance against stripe rust. The same population was analysed at molecular level to explore the genetic diversity for rust resistance. Genetic diversity among 34 selected synthetic hexaploid wheats was studied by random amplified polymorphic DNA (RAPD) analysis. A set of 12 RAPD primers was applied, and the level of polymorphism was found to be 46.67%. The coefficients in the range of 71–100% were detected by genetic similarity matrix based on Nei and Li's index. These coefficients were used for constructing a dendrogram using unweighted pair group of arithmetic means. Synthetic hexaploid line 34 was found to exhibit maximum genetic distances among the 34 selected lines. The same accession also showed excellent phenotypic characters with above average grain weight. These synthetic hexaploids carrying genetic potential for stripe rust resistance and morphological traits should be useful for improvement of existing wheat cultivars.     

Identification of molecular markers for the detection of the yellow rust resistance gene Yr17 in wheat

The Yr17 gene, which is present in many European wheat cultivars, displays yellow rust resistance at the seedling stage. The gene introduced into chromosome 2A from Aegilops ventricosa was previously found to be closely linked (0.5 cM) to leaf and stem rust resistance genes Lr37 and Sr38, respectively. The objective of this study was to identify molecular markers linked to the Yr17 gene. We screened with RAPD primers, for polymorphism, the DNAs of cv. Thatcher and the leaf rust-resistant near-isogenic line (NIL) RL 6081 of cv. Thatcher carrying the Lr37 gene. Using a F2 progeny of the cross between VPM1 (resistant) and Thésée (susceptible), the RAPD marker OP-Y15580 was found to be closely linked to the Yr17 gene. We converted the OP- Y15580 RAPD marker into a sequence characterized amplified region (SCAR). This SCAR marker (SC-Y15) was linked at 0.8 ± 0.7 cM to the Yr17 resistance gene. We tested the SC-Y15 marker over a survey of 37 wheat cultivars in order to verify its consistency in different genetic backgrounds and to explain the resistance of some cultivars against yellow rust. Moreover, we showed that the Xpsr150-2Mv locus marker of Lr gene described by Bonhomme et al. [6] which possesses A. ventricosa introgression on the 2A chromosome was also closely linked to the Yr17 gene. Both the SCAR SC-Y15 and Xpsr150-2Mv markers should be used in breeding programmes in order to detect the cluster of the three genes Yr17, Lr37 and Sr38 in cross progenies. This revised version was published online in June 2006 with corrections to the Cover Date.     

Isolation of microsatellite loci from expressed sequence tag library of Puccinia striiformis f. sp. tritici

We described twenty polymorphic microsatellite loci derived from the expressed sequence tags of Puccinia striiformis f. sp. tritici, which causes yellow rust disease on wheat. The numbers of alleles range from two to six and eight microsatellite loci show significant similarities to known genes. Observed and expected heterozygosities ranged from 0.12 to 0.78 and from 0.24 to 0.87, respectively.     

国内重要抗源品种水源11、水源92及Hybrid46抗条锈基因关系分析

小麦著名抗源品种水源11、水源92及Hybrid46在我国小麦抗病育种中发挥了重要作用,为了明确其抗锈 遗传规律,研究用条中29号及其弱株突变系CY29-mut3,分别接种这3个品种的双列杂交F2、F3代各株系幼苗。结果表明,水源11、水源92与Hybrid46所含抗条锈基因不同,而同来自朝鲜的品种水源11、水源92可能含相同的或完全连锁的抗条锈基因。水源92有3对基因抗中国条锈小种,且不同小种及细胞质对基因表达都有影响,水源92为父本时分别对CY29-mut3及条中29号小种有3对显性基因起抵抗作用（其中两对基因表现为累加作用）;而当水源92为母本时分别对CY29-mut3及条中29号小种有1对完全显性基因和两对隐性基因表达抗病作用。国际已知基因品种Hybrid46为母本时对CY29-mut3有两对基因起作用（可能是两对隐性基因,也可能是存在累加作用的两对显性基因）,而对CY-29小种有3对独立遗传的显性基因表达抗病作用。     

抗条锈病小麦—中间偃麦草异附加系的生化与分子标记

对小麦-中间偃麦草部分双二倍体无芒中4、异附加系C076、宛7107和中国春进行了肽链内切酶（EP-1）等电聚焦电泳。结果表明,肽链内切酶在阳极处有一特异带。肽链内切酶已定位于小麦第7部分同源群,故附加的染色体为第7部分同源群的2条染色体,对中间偃麦草,无芒中4、C076和宛7107进行了RAPD分析。获得了可用于检测C076中外源染色体的3个RAPD标记,即OPI05-800、OPI10-600、OPK01-900。     

Genetic research as the valid base of strategies for breeding rust resistant wheats

It is known that few wheat cultivars maintain their resistance to rust diseases for a long period of time, particularly when crop populations become genetically more uniform. A number of genetically diverse, so far unexploited, sources of rust resistance in the natural as well as mutagenized population of wheat cultivars were identified. Several of these genes were placed in agronomically superior well-adapted backgrounds so that they could be used as pre-breeding stocks for introducing genetic diversity for resistance in a crop population. Some of these stocks when employed as parents in several cross combinations in a breeding programme have generated a number of promising cultivars with diversity for resistance.Many presently grown wheats in India, near-isogenic lines each with Lr14b, Lr14ab, Lr30 and certain international cultivars were identified as possessing diverse sources of adult plant resistance (APR) to leaf rust. Prolonged leaf rust resistance in some of the Indian cultivars was attributed to the likely presence of Lr34 either alone or in combination with other APR components. Tests of allelism carried out in certain cultivars that continue to show adequate levels of field resistance confirm the presence of Lr34, which explains the role that this gene has played in imparting durability for resistance to leaf rust. Also, Lr34 in combination with other APR components increases the levels of resistance, which suggests that combination of certain APR components should be another important strategy for breeding cultivars conferring durable and adequate levels of resistance. A new adult plant leaf rust resistance source that seems to be associated with durability in Arjun has been postulated. Likewise, cultivars possessing Sr2 in combination with certain other specific genes have maintained resistance to stem rust.Further, non-specific resistances that were transferred across widely different genotypes into two of the popular Indian wheats provided easily usable materials to the national breeding programmes for imparting durable resistance to stripe rust.     

The Use of Detached Seedling Leaves of Triticum aestivum to Study Pathogenicity in Puccinia recondita f. sp. tritici

A method is described for establishing isolates of Puccinia recondita f. sp. tritici (causal agent of brown rust of wheat) on detached seedling leaf segments. The method was used to compare the responses of leaf segments and intact seedling leaves for 28 differential genotypes inoculated with eight rust isolates. Leaf segments were incubated at two post-inoculation temperatures (17 and 23C) and intact seedlings at 20–25 C. Reliable determinations of isolate pathogenicity was obtained using detached leaf segments of wheats with genes Lr l. Lr2a, Lr3a, Lr3bg., Lr3ka, Lr9, Lr15, Lrl9. Lr20, Lr24, Lr25. Lr26, Lr28, and Lr30 at both post-inoculation temperatures, and for wheats with genes Lr2b. Lr2c, Lrl7, Lr23, Lr27 + Lr31 and LrH, at 23°C. Differences between leaf segments and intact leaves for the remaining eight differentials were attributed to inconsistent or poor expression of genes in detached leaf segments. By repeating tests with detached leaf segments, it was possible to establish the pathogenicities of the isolates on all of these differentials except those carrying Lr13, Lr14a, Lr16 and Lr18. Potential uses and limitations of the technique in studies of Puccinia recondita f. sp. tritici are discussed.