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Development of PCR markers linked to resistance to wheat streak mosaic virus in wheat
Abstract
Wheat streak mosaic virus (WSMV), vectored by the wheat curl mite (Acer tulipae), is an important disease of wheat (Triticum aestivum L.) in the North American Great Plains. Resistant varieties have not been developed for two primary reasons. First, useful sources of resistance have not been available, and second, field screening for virus resistance is laborious and beyond the scope of most breeding programs. The first problem may have been overcome by the development of resistance to both the mite and the virus by the introgression of resistance genes from wild relatives of wheat. To help address the second problem, we have developed polymerase chain reaction (PCR) markers linked to the WSMV resistance gene Wsm1. Wsm1 is contained on a translocated segment from Agropyron intermedium. One sequence-tagged-site (STS) primer set (WG232) and one RAPD marker were found to be linked to the translocation containing Wsm1. The diagnostic RAPD band was cloned and sequenced to allow the design of specific PCR primers. The PCR primers should be useful for transferring Wsm1 into locally adapted cultivars.
... All randomly selected sister-lines and replications of checks, were screened for a DNA marker linked to the Wsm1 resistance gene (Talbert et al., 1996). For each entry, eight to ten seed were aligned in Cyg germination pouches obtained from Mega International (West Saint Paul, MN), and grown for 10 days in an incubation chamber set at 27 @BULLET C. The seedling leaf tissue, 1.5 to 2 inches in length, was harvested and the DNA was isolated and extracted as per procedures described in Dweikat et al. (2002). ...
... For each entry, eight to ten seed were aligned in Cyg germination pouches obtained from Mega International (West Saint Paul, MN), and grown for 10 days in an incubation chamber set at 27 @BULLET C. The seedling leaf tissue, 1.5 to 2 inches in length, was harvested and the DNA was isolated and extracted as per procedures described in Dweikat et al. (2002). Primers STSJ15L and STSJ15R (Talbert et al., 1996 ) were purchased from Invitrogen Life Technologies (Carlsbad, CA). The Polymerase Chain Reaction (PCR) method was as described in Talbert et al. (1996). ...
... Primers STSJ15L and STSJ15R (Talbert et al., 1996 ) were purchased from Invitrogen Life Technologies (Carlsbad, CA). The Polymerase Chain Reaction (PCR) method was as described in Talbert et al. (1996). The amplified products were fractionated on a 1.5% agarose gel containing ethidium bromide. ...
Wheat streak mosaic virus (WSMV) is one of the most important diseases limiting winter wheat (Triticum aestivum L.) production in the western Great Plains of North America. There is no known effective WSMV resistance within the primary gene pool of wheat. However, a resistance gene (Wsm1) has been transferred to wheat from a perennial relative, intermediate wheat-grass [Thinopyrum intermedium (Host) Barkworth & DR Dewey]. Nebraska-adapted winter wheat lines carrying Wsm1 were used to characterize the effects of this alien introgression on agronomic and quality traits. Sister-lines from six breeding populations were evaluated under virus-free conditions, and under a naturally occurring viral infection. In uninfected locations, no significant difference for grain yield was detected between resistant (R) and susceptible (S) lines, when averaged over populations, but resistant lines had significantly higher test weights. Within populations, significantly higher grain yield was observed only in population 1, while significantly higher test weights occurred in populations 1, 2, 5 and 6. At the infected location, resistant lines were significantly higher in yield in five of six populations. In two of six populations, susceptible lines were significantly higher in bread loaf volume and bake mix time, while in the remaining populations, no significant quality differences were observed. As the Wsm1 gene provided yield advantages under viral infection, and there was no yield detriment in the absence of the virus, its deployment in hard winter wheat cultivars merits consideration.
... The primary objective of this study was to evaluate the pleiotropic effects of the T4DL·4DS-4J s S rec213 translocation carrying Wsm1 on agronomic performance in the absence of disease in hard winter wheat germplasm in the Great Plains production environments using near-isogenic sib-pair families. In the course of conducting this study, we recognized that the established DNA marker for Wsm1 for the shortened translocations, BG263898-STS (Qi et al., 2007), like the marker for the whole arm translocation, STSJ15 (Talbert et al., 1996), is suboptimal for breeding purposes because it is a dominant marker for the presence of Wsm1, and the marker relies on electrophoretic detection. Therefore, the second objective of our study was to develop a high throughput, codominant marker assay for Wsm1 based on the Kompetitive Allele-Specific PCR (KASP; Semagn et al., 2014) amplification platform. ...
Wheat streak mosaic virus (WSMV) is a mite‐vectored virus with substantial economic impact on wheat production. One of the effective sources of resistance to WSMV, Wsm1, is carried on a translocation from Thinopyrum intermedium. The original whole arm form of this translocation (T4DL·4JsS) was highly effective against WSMV but carried a substantial yield penalty in the absence of the virus. Shorter recombinants of the Th. intermedium translocation are now available. This study characterized the agronomic performance of near‐isogenic sib‐pair families in ten yield trials using one of these shortened T4DL·4DS‐4JsS translocations, named ‘rec213’, in the absence of visible disease. This translocation had no effect on heading date, was associated with a modest reduction (≤ 4.8 cm) in plant height, and the translocation had a favorable effect (≤ 12.6%) on grain yield in those environments where highly significant genotype effects were detected. The translocation did not affect protein concentration or lactic acid‐sodium dodecyl sulfate solvent retention capacity, a measure of gluten quality. However, families with the translocation had slightly (≤ 5%) lower protein quality scores than paired families without the translocation. We do not expect this modest difference in quality to be a barrier to utilization of the rec213 translocation for Wsm1, but we encourage breeders to work within high quality genetic backgrounds in when using the rec213 translocation, and to monitor the quality of breeding selections. Improved codominant PCR‐based marker assays were developed to facilitate the use of the rec213 Wsm1 trait in breeding programs. This article is protected by copyright. All rights reserved
... Haynaldia villosa Qi et al., 1995 Pm25 T. monococcum Shi et al., 1998 Wheat streak mosaic virus Wsm1 Ag. elongatum Talbert et al., 1996 Karnal bunt QTL T. turgidum Nelson et al., 1998 Barley Genetic resources such as land races, wild relatives, and synthetic wheats have been reported as novel sources for improving wheat grain quality (Ogbonnaya et al., 2013). Several studies assessing the diversity across wheat gene pools for Zn and Fe grain content have been carried out and candidates with improved Zn and Fe allocation to the grain were found (Ortiz- Monasterio et al., 2007). ...
... Haynaldia villosa Qi et al., 1995 Pm25 T. monococcum Shi et al., 1998 Wheat streak mosaic virus Wsm1 Ag. elongatum Talbert et al., 1996 Karnal bunt QTL T. turgidum Nelson et al., 1998 Barley Genetic resources such as land races, wild relatives, and synthetic wheats have been reported as novel sources for improving wheat grain quality (Ogbonnaya et al., 2013). Several studies assessing the diversity across wheat gene pools for Zn and Fe grain content have been carried out and candidates with improved Zn and Fe allocation to the grain were found (Ortiz- Monasterio et al., 2007). ...
... It was also reported that the 7E chromosome possesses high resistance to Fusarium head blight, so it is of great interest to breeders [58,59]. Although several markers have been designed to map these traits and used for marker-assisted selection [60][61][62], some of them are labourious and time-consuming to use or sometimes lose genetic linkage to the gene of interest. The COS marker technology offers an advantage for the targeted development of markers tightly linked to genes, as demonstrated by Burt and Nicholson [39], who developed markers to map the Aegilops ventricosa-derived Pch1 eyespot resistance in wheat. ...
Thinopyrum elongatum (Host) D.R. Dewey has served as an important gene source for wheat breeding improvement for many years. The exact characterization of its chromosomes is important for the detailed analysis of prebreeding materials produced with this species. The major aim of this study was to identify and characterize new molecular markers to be used for the rapid analysis of E genome chromatin in wheat background. Sixty of the 169 conserved orthologous set (COS) markers tested on diverse wheat-Th. elongatum disomic/ditelosomic addition lines were assigned to various Th. elongatum chromosomes and will be used for marker-assisted selection. The macrosyntenic relationship between the wheat and Th. elongatum genomes was investigated using EST sequences. Several rearrangements were revealed in homoeologous chromosome groups 2, 5, 6 and 7, while chromosomes 1 and 4 were conserved. Molecular cytogenetic and marker analysis showed the presence of rearranged chromosome involved in 6ES and 2EL arms in the 6E disomic addition line. The selected chromosome arm-specific COS markers will make it possible to identify gene introgressions in breeding programmes and will also be useful in the development of new chromosome-specific markers, evolutionary analysis and gene mapping.
... RonL , have been detected. PCR-based markers for the detection of these genes (Talbert et al., 1996) and for the detection of additional introgressions from Th. intermedium have been developed (Chen et al., 2003). The lines containing the gene Wsm1 and all partial amphiploid lines, except cv. ...
Over the last 100 years, research in barley disease resistance has progressed from classical genetic approaches up to molecular genetics and genome-wide functional profiling. Along the way, a multitude of well-characterized genetic resources have paved the way for mechanistic investigations into barley immunity. Seminal discoveries in barley have been translated to other crops, thus proving it to be an excellent system for plant disease research. Recent access to high-quality barley and pathogen genomes has empowered large-scale functional studies and facilitated the development of new technologies to associate traits with genes. Continued integration of existing germplasm with anchored sequence data promises to expedite mapping and functional characterization of important disease traits. In this chapter, we offer a genomic view of barley biotic stress with a focus on different types of resistance, current genomic approaches to dissect immune responses, and future prospects for the field.
... RonL , have been detected. PCR-based markers for the detection of these genes (Talbert et al., 1996) and for the detection of additional introgressions from Th. intermedium have been developed (Chen et al., 2003). The lines containing the gene Wsm1 and all partial amphiploid lines, except cv. ...
... Detection of Th. intermedium chromatin. PCR markers STS-J15 and WSR11 produced characteristic amplicons of approximately 420 and 200 bp, respectively (Talbert et al., 1996;Fahim et al., 2012). Both markers detected polymorphism among the resistant and susceptible lines and the presence of a marker band related to the Wsm1 resistance gene (Supplementary Figure S1). ...
Pyramiding of alien-derived Wheat streak mosaic virus (WSMV) resistance and resistance enhancing genes in wheat is a cost-effective and environmentally safe strategy for disease control. PCR-based markers and cytogenetic analysis with genomic in situ hybridisation were applied to identify alien chromatin in four genetically diverse populations of wheat (Triticum aestivum) lines incorporating chromosome segments from Thinopyrum intermedium and Secale cereale (rye). Out of 20 experimental lines, 10 carried Th. intermedium chromatin as T4DL*4Ai#2S translocations, while, unexpectedly, 7 lines were positive for alien chromatin (Th. intermedium or rye) on chromosome 1B. The newly described rye 1RS chromatin, transmitted from early in the pedigree, was associated with enhanced WSMV resistance. Under field conditions, the 1RS chromatin alone showed some resistance, while together with the Th. intermedium 4Ai#2S offered superior resistance to that demonstrated by the known resistant cultivar Mace. Most alien wheat lines carry whole chromosome arms, and it is notable that these lines showed intra-arm recombination within the 1BS arm. The translocation breakpoints between 1BS and alien chromatin fell in three categories: (i) at or near to the centromere, (ii) intercalary between markers UL-Thin5 and Xgwm1130 and (iii) towards the telomere between Xgwm0911 and Xbarc194. Labelled genomic Th. intermedium DNA hybridised to the rye 1RS chromatin under high stringency conditions, indicating the presence of shared tandem repeats among the cereals. The novel small alien fragments may explain the difficulty in developing well-adapted lines carrying Wsm1 despite improved tolerance to the virus. The results will facilitate directed chromosome engineering producing agronomically desirable WSMV-resistant germplasm.Heredity advance online publication, 1 June 2016; doi:10.1038/hdy.2016.36.
... As many as 40 genes of interest have been mapped to this chromosome to date, including some encoding resistance/ tolerance to biotic and abiotic stress (Chen et al., 1995(Chen et al., , 2005Effertz et al., 2001;Nga et al., 2009;Paull et al., 1998;Talbert et al., 1996), and various agronomic traits (Araki et al., 1999;Bai et al., 2008;Bö rner et al., 2002;Keller et al., 1999;McCartney et al., 2005;Sourdille et al., 2002). Detailed information on the chromosome gene order would greatly enhance effective use of the genes in breeding programs and ultimately in their cloning and functional analysis. ...
Wheat is the third most important crop for human nutrition in the world. The availability of high-resolution genetic and physical maps and ultimately a complete genome sequence holds great promise for breeding improved varieties to cope with increasing food demand under the conditions of changing global climate. However, the large size of the bread wheat (Triticum aestivum) genome (approximately 17 Gb/1C) and the triplication of genic sequence resulting from its hexaploid status have impeded genome sequencing of this important crop species. Here we describe the use of mitotic chromosome flow sorting to separately purify and then shotgun-sequence a pair of telocentric chromosomes that together form chromosome 4A (856 Mb/1C) of wheat. The isolation of this much reduced template and the consequent avoidance of the problem of sequence duplication, in conjunction with synteny-based comparisons with other grass genomes, have facilitated construction of an ordered gene map of chromosome 4A, embracing ‡85% of its total gene content, and have enabled precise localization of the various translocation and inversion breakpoints on chromosome 4A that differentiate it from its progenitor chromosome in the A genome diploid donor. The gene map of chromosome 4A, together with the emerging sequences of homoeologous wheat chromosome groups 4, 5 and 7, represent unique resources that will allow us to obtain new insights into the evolutionary dynamics between homoeologous chromosomes and syntenic chromosomal regions.
... Near-isogenic lines (NILs) have been used to select molecular markers linked to resistance genes (Young et al. 1988). A similar strategy, based on the use of recombinant lines carrying short chromosome segments introgressed from related species, has been applied for selective identification, by differential analysis, of molecular markers detecting polymorphisms between alien and substituted DNA (Schachermayr et al. 1994(Schachermayr et al. , 1995Autrique et al. 1995;Procunier et al. 1995;Qi et al. 1996;Talbert et al. 1996). ...
... Since they are based on a specific sequence, STS markers more reliably detect the same locus. There are several instances where RFLP and AFLP markers have been converted to STS markers for use in genetic mapping (Paran and Michelmore, 1993;Schachermayr et al., 1997;Feuillet et al., 1995;Dedryver et al., 1996;Talbert et al., 1996;Blair and McCouch, 1997;Huang et al., 1997;Paltridge et al., 1998;Toojinda et al., 1998;Mohler et al., 2001). This marker system can hence be best utilized in pearl millet for both mapping studies and MAS, provided polymorphism detected is adequate (Hash and Bramel-Cox, 2000). ...
... 65 random primers were tried to study polymorphism among recurrent and donor parents and their isogenic line ( Table 1). Some genes of agronomic importance, however, have been tagged with RAPD markers in tomato [11,12], in rice [13][14][15], and in wheat [16][17][18][19]. The three primers (OPA-19, OPD-12, OPJ-10) were polymorphic between WL711 and other stocks. ...
Sixty-five random amplified polymorphic DNA (RAPD) primers were used for the detection of polymorphism among recipient and donor parents and their isogenic lines linked to leaf rust resistance genes, Lr9 and the resistant gene in kharchia local mutant KLM4-3B. Three primers showed polymorphism among recurrent parent, donor parent and isogenic lines.
... Wsm1 was located on chromosome translocation 4DL.4AgS. A marker STSJ15 with the target polymerase chain reaction (PCR) fragment of 241 bp is diagnostic for this gene (Seifers et al., 2007;Talbert et al., 1996). Several new markers based on expressed sequence tag (EST) sequences from wheat chromosome 4DS were reported (Qi et al., 2007) and the STS marker XBG263898 is also used to screen for Wsm1. ...
Biotic stresses including diseases [leaf, stem and stripe rusts, and wheat streak mosaic virus (WSMV)] and insects [greenbug (GB), Hessian fly (Hf), Russian wheat aphid (RWA) and wheat curl mite (WCM)] significantly affect grain yield and end-use quality of hard winter wheat (HWW, Triticum aestivum L.) in the U.S. Great Plains. Many genes or quantitative traits loci (QTL) have been identified for seedling or adult plant resistance to these stresses. Molecular markers for these genes or QTL have been identified using mapping or cloning. This study summarizes the markers associated with various genes including genes or QTL conferring resistances to insects, such as GB (7), RWA (4), Hf (9), and WCM (4) and diseases including leaf, stem and stripe rusts (26) and WSMV (2); genes or QTL for end-use quality traits such as high (3) and low (13) molecular weight glutenin subunits, gliadin (3), polyphenol oxidase (2), granule-bound starch synthase (3), puroindoline (2), and pre-harvesting sprouting (1); genes on rye translocations with 1AL and 1BL; and genes associated with plant height (12) and photoperiod sensitivity (1). A subset of the markers was validated using a set of diverse wheat lines developed by breeding programs in the Great Plains. These analyses showed that most markers are diagnostic in only limited genetic backgrounds. However, some markers developed from the gene sequences or alien fragments are highly diagnostic across various backgrounds, such as Rht-B1, Rht-D1, Ppd-D1, Glu-D1, Glu-A1, and 1AL.1RS. Knowledge of both genotype and phenotype of advanced breeding lines could help breeders to select right parents to integrate various genes into new cultivars and increase the efficiency of wheat breeding.
... Beginning with the BC 1 generation, the sequence-tagged-site (STS) marker STSJ15 that is specific for the translocated segment carrying Wsm1 gene (Talbert et al. 1996), was used to select resistant plants. Since the gene is a translocated alien fragment, it no longer recombines with wheat chromatin. ...
... Wsm1 was located on chromosome translocation 4DL.4AgS. A marker STSJ15 with the target polymerase chain reaction (PCR) fragment of 241 bp is diagnostic for this gene (Seifers et al., 2007;Talbert et al., 1996). Several new markers based on expressed sequence tag (EST) sequences from wheat chromosome 4DS were reported (Qi et al., 2007) and the STS marker XBG263898 is also used to screen for Wsm1. ...
Biotic stresses including diseases (leaf, stem and stripe rusts), arthropods (greenbug [GB], Hessian fly [Hf], Russian wheat aphid [RWA], and wheat curl mite [WCM]) and their transmitted viral diseases significantly affect grain yield and end-use quality of hard winter wheat (Triticum aestivum L.) in the U.S. Great Plains. Many genes or quantitative trait loci (QTL) have been identified for seedling or adult-plant resistance to these stresses. Molecular markers for these genes or QTL have been identified using mapping or cloning. This study summarizes the markers associated with various effective genes, including genes or QTL conferring resistances to arthropods, such as GB (7), RWA (4), Hf (9), and WCM (4) and diseases including leaf, stem and stripe rusts (26) and Wheat streak mosaic virus (WSMV; 2); genes or QTL for end-use quality traits such as high (3) and low (13) molecular weight glutenin subunits, gliadin (3), polyphenol oxidase (2), granule-bound starch synthase (3), puroindoline (2), and preharvesting sprouting (1); genes on wheat–rye (Secale cereale L.) chromosomal translocations of 1AL.1RS and 1BL.1RS; and genes controlling plant height (12), photoperiod sensitivity (1), and vernalization (2). A subset of the markers was validated using a set of diverse wheat lines developed by breeding programs in the Great Plains. These analyses showed that most markers are diagnostic in only limited genetic backgrounds. However, some markers developed from the gene sequences or alien fragments are highly diagnostic across various backgrounds, such as those markers linked to Rht-B1, Rht-D1, Ppd-D1, Glu-D1, Glu-A1, and 1AL.1RS. Knowledge of both genotype and phenotype of advanced breeding lines could help breeders to select the optimal parents to integrate various genes into new cultivars and increase the efficiency of wheat breeding.
... In each backcross, DNA extraction and polymerase chain reaction (PCR) analysis was performed as outlined in Randhawa et al., 2009. Beginning with the BC 1 generation, the sequence-tagged-site (STS) primers STSJ15L and STSJ15R, which are specifi c for the translocated segment carrying the Wsm1 gene (Talbert et al., 1996), was used to select the plants carrying the Wsm1 gene. STSJ15 is a dominant marker amplifying a 400-bp band from the donor parent. ...
Seven winter wheat (Triticum aestivum L.) germplasm lines carrying the Wsm1 gene conferring resistance to Wheat streak mosaic virus (WSMV)-Alliance-Wsm1 (Reg. No. GP-858, PI 653710), Arrowsmith-Wsm1 (Reg. No. GP-859, PI 653711), Goodstreak-Wsm1 (Reg. No. GP-860, PI 653712), Harry-Wsm1 (Reg. No. GP-861, PI 653713), Millennium-Wsm1 (Reg. No. GP-862, PI 653714), Wahoo-Wsm1 (Reg. No. GP-863, PI 653715), and Wesley-Wsm1 (Reg. No. GP-864, PI 653716)-were codeveloped by Washington State University, Pullman, WA; the University of Nebraska, Lincoln, NE; and the USDA-ARS. These seven different winter wheat cultivars were selected to provide more sources of effective resistance to WSMV in winter wheat cultivars of Nebraska and adjoining states. Resistance to WSMV is conferred by the Wsm1 gene, which was translocated from Thinopyrum intermedium (Host) Barkworth & D.R. Dewey [Agropyron intermedium (Horst.) Beauv.] into wheat. The STSJ15 marker was used to select for the gene in the backcross progeny until the BC 4F 1 generation. In BC 4F 2 generation, screening for disease resistance was done using the Sidney 81 isolate of WSMV, along with the recurrent parents. Lines showing high levels of resistance to WSMV were further selected for seed increase and field evaluation. These lines may serve as a winter wheat source of WSMV resistance and may be used for gene pyramiding and for studying the effect of the Wsm1 gene in different backgrounds.
... SSR Two markers flanked at (4.0) and (6.4) 2A7A Zhou et al., 2011 resistance to stripe rust Yrxy1 RGAP M8 (2.3) and M9 (3.5) SSR Xbarc49 (15.8) and Xwmc422 (26.1) Streak mosaic virus Wsm1 STS Wg232 (tight) 4L Talbert et al., 1996 ...
Molecular markers have extensively been used for tagging and mapping of genes and QTLs conferring resistance to biotic and abiotic stresses. These tools have also been used for screening of germplasms, fingerprinting, and marker -assisted breeding in crop systems. This chapter present s an over-view on the basic concepts of molecular map ping and marker -assisted breeding and its most widely used applications in crop improvement programs, viz., marker-assisted backcross breeding , gene introgression,
gene pyramiding, and marker -assisted selection at an early generation, with emphasis on stress -related traits and examples from several crops. We have also discussed some quantitative aspects of marker-based introgression, backcross breeding, and gene pyramiding programs. We have
also added a note on breeding by design and genomic selection as tools for future breeding endeavors aiming at introgression of stress resistance into high-yielding cultivars . Harnessing the full potential of marker -aided breeding for improvement of stress resistance in crop systems will require a multidisciplinary approach and integrated know ledge of the molecular and physiological processes influencing the stress -related traits. Hence, marker -aided breeding for stress resistance in the post-genomic era poses
great challenge for molecular breeders to realize the tar get objectives .
... Wsm1 cosegregated with a STS amplified by the primer set STSJ15 Liang et al . ( 1979 ) ; Wang et al . ( 1980 ) ; Friebe et al . ( 1991 ) ; Talbert et al . ( 1996 ) ...
Wheatgrass and wildrye grasses are some of the most important grasses in the temperate regions of the world (Asay and Jensen 1996a, b). These drought-resistant grasses are excellent sources of forage and habitat for livestock and wildlife; and they are valued for weed control, habitat use, soil stabilization, and watershed management. Many of these grasses are related to and have been hybridized with cultivated cereal crops including wheat (Triticum aestivum L. and T. durum Desf.), barley (Hordeum vulgare L.), and rye (Secale cereale L.) as genetic sources for disease resistance, salinity tolerance, and other traits. These hybrids were summarized in several early review articles (Sharma and Gill 1983; Dewey 1984; Wang 1989a). Since then, certain specific subjects of alien gene transfer from wild Triticeae into wheat have been extensively reviewed and discussed (Knott 1989; Pienaar 1990; Jiang et al. 1994b; Friebe et al. 1996; Fedak 1999; Jauhar and Chibbar 1999; Repellin et al. 2001; Sahrawat et al. 2003; Jauhar 2006; Qi et al. 2007; Trethowan and Mujeeb-Kazi 2008). The taxonomy of the wheatgrass and wildrye grasses has been the object of considerable controversy. Even with the advent of molecular phylogenetics, Kellogg (2006) stated that "generic relationships within Triti-ceae have always been and remain problematic." In North America, the wheatgrasses traditionally have been included in the genus Agropyron, and the wildryes have largely been treated as species in the genus Elymus (Bowden 1965; Hitchcock 1971). Depending on how the genus Agropyron was treated, the number of species in this genus varied. Bentham (1882) included about 20 species in Agropyron, whereas Hackel (1887) listed 32 species. More recently, however, taxonomic realign-ments have been proposed that are based on genomic or biological relationships as well as plant morphology (Tsvelev 1976; Dewey 1984; Yen et al. 2005b). Dewey (1984) proposed that Agropyron be restricted to species of the crested wheatgrass complex, a polyploid series based on the P-genome. Thus, bluebunch wheatgrass, previously A. spicatum (Pursh) Scribner & Smith, and related species based on the St-genome are now included in the genus Pseudoroegneria A. Löve. Tall wheatgrass and intermediate wheatgrass are now included in the genus Thinopyrum A. Löve as Th. ponticum (Podp.) Barkworth & D.R. Dewey and Th. intermedium (Host) Barkworth & D.R. Dewey, respectively. Species in this genus possess the J-or E-genome, which Dewey (1984) designated as "J ¼ E," and sometimes also contains the St-genome (Liu and Wang 1993; Kishii et al. 2005). Slender wheatgrass, previously A. trachycaulum (Link) Malte ex H.F. Lewis, and its self-fertile caespitose relatives are in the genus Elymus along with several wildryes. This genus is based on the St-genome, in combination with one or more of H-, Y-, W-, or P-genomes (Wang et al. 1995). Depending on the taxonomic treatment, between 200 and 250 wheatgrass and wildrye species have been described worldwide (Asay and Jensen 1996a, b). More than two-thirds are native to Eurasia and about 22 to 30 are considered native to North America.
... Polymerase chain reaction (PCR)-based markers such as sequence-tagged-site (STS) markers are important to plant breeding programmes and genome analysis because they are simple, fast, cheap and easy to handle. Primers are usually designed from sequences of previously mapped molecular markers including random amplified polymorphic DNA (RAPD) (Talbert et al. 1996; Deng et al. 1997; Kawchuk et al. 1998 ), restriction fragment length polymorphisms (RFLPs) (Blake et al. 1996; Erpelding et al. 1996; Williams et al. 1996; Tsumura et al. 1997; Blair and McCouch 1997; Harry et al. 1998) and amplified fragment length polymorphisms (AFLPs) (de Jong et al. 1997; Qu et al. 1998; Bradeen and Simon 1998). Polymorphisms are detected either from direct amplification with the primer pairs or after digestion of the PCR products with restriction enzymes. ...
For a simple, rapid and PCR-based screening of sex in the cultivated asparagus (Asparagus officinalis L.), we developed five STS markers from previously mapped, low-copy, sex-linked AFLP markers. A male/female PCR assay was
feasible with these STS markers either by direct amplification or by digestion with restriction enzymes. Similar to the AFLP
markers from which they were derived, STS4150.1, STS4150.2, STS4150.3 and STS3156 did not give recombinants in five different
populations. STS3660 could be scored codominantly, enabling the differentiation of XY from YY males in the screened F2 mapping population. The use of the sex-linked STS markers should allow early identification of sex, thus accelerating the
breeding process for new asparagus varieties. Further, 10 additional AFLP markers obtained with PstI/MseI primer combinations have been mapped on the L5 chromosome, bringing the total number of known AFLP and STS markers flanking
the sex locus to 24. These markers can be utilized for fine mapping of the sex gene in asparagus, which will pave the way
for a map-based cloning approach.
Sugarcane aphids Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae) have recently become an eruptive and costly pest of sorghum, Sorghum bicolor (L). In contrast to its southern range in the United States, sugarcane aphid colonizes sorghum at flowering or just post-bloom in the central High Plains. Thus the goal of this work was to quantify how sorghum resistance (commercially available hybrid DKS37-07), timing of planting (early or conventional plant date), and insecticide seed treatment (clothianidin) affected population dynamics of sugarcane aphids in late-colonized sorghum in the central High Plains. The impacts of these factors on sugarcane aphid densities were measured over two growing seasons, and the numbers of natural enemies of the aphids were quantified as well. Host plant resistance emerged as the main driver of sugarcane aphid population dynamics while planting date and seed treatment had a variable impact on M. sacchari and their predators. Host plant resistance also affected predators of sugarcane aphids and, while not directly explored in this study, potentially altered predator-aphid interactions as well. Diverse natural enemies including Coccinellidae, Syrphidae, Chrysophidae, and Anthocoridae were readily recruited by sugarcane aphid infestations, and predators were strongly correlated with populations of M. sacchari regardless of the seed treatment application or sorghum variety and across planting dates. This research demonstrates that a commercially available resistant sorghum variety provides the most robust protection against this pest in the central High Plains. Further, an already present assemblage of aphid predators recruits readily to aphid-infested sorghum and is likely to provide important biological control services particularly in resistant sorghum.
The development of wheat ( Triticum aestivum L.) cultivars that are resistant to Wheat streak mosaic virus (WSMV), yet competitive in yield under nondiseased conditions, is an objective for breeding programs in the Great Plains. This field study was conducted to compare classical and transgenic sources of resistance to WSMV. Three sets of germplasm were evaluated. These included adapted cultivars with various levels of tolerance, transgenic wheat lines containing viral coat protein or replicase sequences from WSMV that showed resistance in greenhouse trials, and germplasm with resistance to WSMV due to a translocated segment of chromosome 4Ai‐2 from Thinopyrum intermedium (Host) Barkworth and Dewey containing Wsm1 A replicated field trial was conducted at Bozeman, MT, over a two‐year period to evaluate the effectiveness of these different sources of resistance to mechanical inoculation of WSMV. Adapted cultivars differed in their ability to tolerate WSMV with mean reductions in yield over the two years ranging from 41 to 74%. Incorporation of the replicase or coat protein gene from WSMV did not provide field resistance to viral infection and in general, transgenic lines yielded less than their parent cultivar, ‘Hi‐Line’. Wheat‐ Thinopyrum lines positive for a DNA marker linked to the Wsm1 gene had significantly reduced yield losses ranging from 5 to 39% compared with yield losses of 57 to 88% in near isogenic lines not having the Wsm1 gene. Yield of lines with Wsm1 in the absence of disease ranged from 11 to 28% less than yield of lines without Wsm1 Our results suggest Wsm1 provides the best source of WSMV resistance but a yield penalty may exist because of the presence of the translocation.
Today, the availability of recombinant DNA techniques together with advances in molecular biology and cell culture provides access to a refined understanding of the genome. Our present century is moulded by the invention of the genome structure and the subsequent use of this knowledge in genetics and its applied wing: breeding. Starting with the rediscovery of the Mendelian laws, classical segregation analysis and cytology formed the basis of scientific breeding strategies. Complete DNA sequences of many prokaryotes have been determined, the genome of yeast has been sequenced and it is expected that the base pairs of the model plant Arabidopsis will be sequenced before the end of this century. Although such a sequence analysis provides the most complete information about the genetic basis, it does not inform about the meaning and the functionality of genes. Taking into consideration the enormous size of the genome and the fact that a tremendous number of the base pairs are silent, it seems recommendable to analyse only those parts containing information.
Wheat is the most important and strategic food crop for ensuring food security at the global level. The demand for wheat has been increasing tremendously with the increasing population. The production of wheat globally has increased dramatically from 218.5 million tons in 1961 to 732 million tons in 2013 mainly due to the adoption of semidwarf high-yielding and input-responsive wheat varieties. Wheat genetic resources have played a significant role in wheat improvement by contributing important sources of genes for yield potential, broad adaptation, short plant height, improved grain quality, and resistance/tolerance to major abiotic and biotic stresses. In view of the threat of genetic erosion associated with many natural and anthropogenic factors including climate change and the rapid expansion and domination of mega wheat cultivars across the major wheat agroecologies, efforts have been made to collect and conserve wheat genetic resources ex situ in genebanks. To date more than 900,000 wheat accessions (wild relatives, land races, synthetic wheats, breeding lines, and genetic stocks) are conserved in different genebanks at the global level. Management and utilization of such huge but important genetic resources, however, is a big challenge. Application of modern tools and strategies, such as Focused Identification of Germplasm Strategy, effective gene introgression methods, and genomics, are essential in improving genetic resource utilization and improving breeding efficiency.
Development of wheat (Triticum aestivum L.) cultivars resistant to Wheat streak mosaic virus (WSMV) that remain productive in the absence of the disease would benefit wheat growers. A wheat germplasm (KS93WGRC27) carrying a Thinopyrum intermedium (Host) Barkworth and Dewey chromosome Us translocation conferring WSMV resistance was used to develop spring wheat populations segregating for WSMV resistance. Four populations, consisting of a total of 22 translocation-positive (WSMV-resistant), 36 translocation-negative (WSMV-susceptible), and eight parental lines, were grown as a randomized complete block with three replications at Bozeman and Conrad, NIT, in 1998 and 1999. Treatments were arranged as a split plot with populations as main plots and progeny and parents:as subplots. The agronomic performance of resistant and susceptible lines was compared under inoculated and noninoculated conditions to assess the effectiveness of the WSMV resistance gene and to determine the effects of the Thinopyrum translocation in the absence of disease. A small but significant decrease in yield was observed for noninoculated resistant lines in contrast to susceptible lines. However, the yield range of resistant entries suggests that the recovery of parental yield was possible. The resistance source was highly effective in limiting virus accumulation and yield losses to WSMV, resulting in only a 5% yield reduction in resistant lines under inoculated conditions compared with 32% for susceptible lines. In all instances where WSMV was introduced to field trials, the Thinopyrum translocation provided a significant benefit for resistant lines when compared with susceptible lines. The T. intermedium translocation present in resistant lines had no detrimental effects on end-use quality or other agronomic traits.
The genomic DNA of common wheat (Triticum aestivum L.) "Chinese Spring" (CS) and its ph1b mutant were analyzed by using 19 sequence tagged site PCR (STS-PCR) primers, which derived from RFLP probes from barley ( Hordeum vulgare L.) chromosome 5H. One marker was identified on wheat chromosome 5BL, which is 5.7 cM (centiMorgan) proximal to Ph1 gene, using the CS homoeologous group 5 nullisomic-tetrasomic, ditelosomic 5BL line and an F-2 population from CS x ph1b mutant. This linked PCR marker was converted into a more specific sequence characterized amplified region (SCAR) marker. To obtain a new winter wheat line containing phlb gene, the authors used a nullisomic 5B line of "Abbodanza" as a bridge parent and crossed respectively with the CS ph1b mutant (donor) and a winter wheat variety, "Jing 411" (recipient). The meiotic chromosome pairing was checked in the progeny of each cross, as well as using the marker-assistant selection of the SCAR marker identified for phlb gene.,After three inter-crossing and one selfing, a relatively stable ph1b substitution line of winter wheat with "Jing 411" background way obtained.
As the result of several decades of traditional breeding on the resistance of wheat to viruses, foreign scientists have succeeded in identifying resistance sources (cultivar Geneva, Thinopyrum species) and resistance genes (Bdv1, Bdv2, Bdv3, Wsm1) that can be efficiently used against the cereal viruses attacking wheat, including Barley yellow dwarf viruses (BYDV), Cereal yellow dwarf viruses (CYDV), Wheat streak mosaic virus (WSMV) and Wheat spindle streak mosaic virus (WSSMV). Some of the lines carrying the translocation do not yet have a yield average as high as that of cultivated varieties, though the use of varieties and breeding lines carrying resistance genes is the most effective way of maintaining yield averages in the case of infection. Some lines contain a combination of several resistance genes, and these gene pyramids afford protection against a number of viruses. The mechanism of resistance is partly known (Bdv2), but in some cases further research will be required (cultivar Geneva). The advantage of using resistance sources in wheat has been recognised in Hungary, as elsewheres and it is hoped that they will soon spread on an increasingly wide scale.
Based on the differences of rRNA intergenic sequences between wheat (Triticum aestivum L.) and rye (Secale cereale L.), rye specific primer set NOR-R1 was synthesized according to Koebner' design. PCR analyses were carried out on different DNA substrates of common wheat and its relatives such as Agropyron elongataum (Host) Beauv., Haynaldia villosa Shur. and Hordeum vulgare L. The results confirmed that NOR-R1 primer set is specific to rye. It was found that PCR using DNAs from wheat materials containing 1R chromosome resulted in the specific amplification products of rye, whereas no amplification product was detected in PCR when using DNAs with other rye chromosomes. FISH (Fluorescent in situ Hybridization) further revealed that the binding sites for the primer set NOR-R1 were only on nucleolar organizing region of chromosome 1R. These results indicated that the primer set NOR-R1 provides a useful means for molecular tagging of rye chromosomes 1R in wheat genetic background.
Grain crops, i.e. rice (Oryza sativa), maize (Zea mays), wheat (Triticum aestivum), barley (Hordeum vulgare), and to a lesser extent sorghum (Sorghum bicolor), oats (Avena sativa), and rye (Secale cereale) are of major importance for human nutrition (cf. Anonymous 1994). However, each year sincere yield losses have to be faced in these crops due to fungal and viral diseases as well as insect pests. Therefore, breeding for resistance in order to avoid these losses as well as the application of fungicides and pesticides has to be considered as a major goal in breeding of these cereals. In general, combining of resistances or the introgression of new resistance genes from unadapted germplasms or related species, respectively, is achieved by sexual recombination, i.e. crossing of parental lines followed by phenotypic selection in the segregating offspring. In this case, the success of breeding entirely depends on extensive field or glasshouse tests for resistance to the respective pathogens. However, as grain crops are damaged by many pathogens which often show a rapid adaptation to their hosts’ resistance genes, breeding for resistance is a very complex task and the identification of desired recombinants expressing resistance to most diseases by phenotypic selection only has nearly reached the limits of manageability.
Considerable advances in DNA marker technology in recent years have led to an increased understanding of the complexity of the wheat genome as well as the mapping of a large number of genes of interest. In the process, 60 loci linked to disease and pest resistance have been mapped using different marker applications. Although restriction fragment length polymorphism markers have been the basis for most of this work, useful markers have also been obtained using random amplified polymorphic DNA, sequence characterized amplified regions, amplified fragment length polymorphisms and, most recently, simple sequence repeats. The next challenge facing breeders is the application of these markers in breeding programmes.
Recent developments in DNA-based marker technology have opened up newer avenues for the studies on plant molecular genetics. The new marker systems have enabled researchers to construct genetic maps and to examine directly the genotypes of plant species rather than phenotypes. These markers have also provided means to address problems related to genome structure and evolution, understand the genetic basis of morphological variation, and study the genomic distribution of genes and the pattern of inter- generic/inter-specific gene flow. Genetic maps based on molecular markers have been constructed for a number of plant species such as Arabidopsis thaliana, Brassica species, Oryza sativa, Triticum aestivum, Zea mays, Hordeum vulgare, Pisum sativum, to name a few. The most important and practical application of these maps has been in generating markers linked to both qualitative and quantitative traits of agronomic importance and employing them in marker assisted breeding. The focus of this review is to summarise recent developments in the area of DNA marker technology with special reference to wheat (Triticum aestivum) and Brassica coenospecies and highlight its applications in specific areas of plant breeding.
Genome mapping has emerged as a potential tool that provides the complete depiction of the genomes of plants and animals and thereby the means for their further manipulation. It involves elucidation of the nuclear genome of higher plants and animals as well as the smaller cytoplasmic genomes as chloroplasts and mitochondria. It involves basically linkage mapping employing molecular markers and using mainly segregating populations. First generation or primary genetic linkage maps have been constructed in several plant and animal systems, particularly those of fundamental or of economic interests. An array of markers have been used for such purposes, those included mainly isoenzyme, RFLP, RAPD, AFLP and SSR. The mostly used mapping populations included F2, recombinant inbred lines, backcross, doubled haploid lines and CEPH. The second generation genetic maps, such as high density, high resolution and saturated linkage maps have also been developed in several plants and animals mainly by enriching the primary maps locally or globally. Molecular mapping has paved the way for positioning of simply inherited trait loci (SITL) controlling oligogenic characters and quantitative trait loci (QTL) controlling polygenic characters. These have in turn facilitated marker assisted breeding (MAB) or molecular breeding (MB) for improvement in these traits. It has also recently been possible to mendelize the QTLs for precise monitoring of the gene clusters. Construction of molecular maps of two or more species/genera using a common set of markers and characters have resulted in comparative mapping that provides valuable information on genome homology and thus could illuminate on phylogenetic relationship and evolution in several taxa. Genome mapping has also provided the platform for chromosome walking or chromosome landing for isolating the chromosomal fragment containing a target gene and its (map based) cloning (MBC) for use in genetic transformation.
Wild relatives of common wheat, Triticum aestivum, are an important source for disease and pest resistance. Recently we reviewed the status of wheat-alien translocations conferring resistance to diseases and pests (45). Since then, several new transfers were reported and markers linked to resistance genes identified. Here we present an update of the available information on wheat-alien translocations.
Wheat streak mosaic (WSM), caused by Wheat streak mosaic virus (WSMV), is a devastating disease in wheat (Triticum aestivum L.) in the Great Plains of North America. Use of resistance is an effective and environmentally sound method to control the disease. In this study, six wheat genotypes were compared for their responses to WSMV infection under growth chamber conditions. The three resistant genotypes, KS96HW10-3 (Wsm1), Mace (Wsm1), and CO960293-2, had disease scores significantly lower than the remaining three genotypes without major resistance. Disease in TAM 111 and TAM 112 was consistently less severe than Karl 92. A population consisting of 188 F(2:3) families derived from the cross CO960293-2 x TAM 111 was used for determining inheritance of the WSMV resistance and for molecular mapping of the resistance in CO960293-2. Data on segregation of resistance indicated that the resistance in CO960293-2 is conditioned by a single dominant gene, which was named Wsm2. Transgressive segregation toward susceptibility occurred in the population suggesting a minor gene in the moderately susceptible parent TAM 111, which was not allelic to Wsm2. Wsm2 was mapped to the short arm of chromosome 3B with two flanking simple sequence repeat markers. The single dominant gene inheritance for WSMV resistance in CO960293-2 has been consistent with the observations that the resistance can be readily transferred to adapted cultivars.
The conventional plant breeding is primarily based on phenotypic selection of superior individuals among segregating progenies resulting from hybridization experiments or from natural populations. Although significant strides have been made in crop improvement through phenotypic selection, considerable difficulties are often encountered during this process. Most of the traits considered in plant genetic improvement programmes are quantitative in nature and controlled by many genes, together with environmental factors and underlying genes have small effects on the observable phenotypes. Thus testing procedures are many times difficult and unreliable, due to nature of target traits or the environment. Beside, conventional plant breeding approaches are time consuming. Hence breeders are extremely interested in new technologies that could make these procedures more efficient. Molecular marker assisted selection and breeding offer such a possibility. Where breeding goals cannot be achieved using traditional approaches, there is now considerable scope for using molecular markers to develop new varieties. Several examples of successful marker-assisted selection (MAS) approaches are now emerging. In this chapter we will discuss potentials of marker assisted selection and breeding and some of the successful examples in agriculture, horticulture and forestry.
Today, the world's population is increasing at the most rapid rate ever. Two hundred people are being added to the planet every minute. It is forecast that by the year 2050, the world's population will double to nearly 12 billion people. To feed this population, these people will require a staggering increase in food production. In fact, it has been estimated that the world will need to produce more than twice as much food during the next 50 years as was produced since the beginning of agriculture 10 000 years ago. How will researchers continue to develop improved wheat varieties to feed the world in the future? At least for the foreseeable future, plant breeding as it is known today will play a primary role. What will change are the tools that can be employed. This chapter focuses on current approaches for the use of modern molecular-based technologies to develop improved varieties and discusses areas for future applications. Biotechnology can be defined in many different ways, but for the purpose of this chapter, all areas that use molecular approaches to understand and manipulate a plant genome will be considered. However, for the sake of discussion, the techniques are divided between those that make use of molecular markers for studying the genetic material already present within the wheat plant and genetic engineering aimed at the introduction of novel genetic material. It is the latter that often raises concern and that many believe represents 'modern biotechnology'.
Recent reviews on molecular markers developed for wheat genes have been published by Langridge and Chalmers (1998) and Gupta et al. (1999), while updated lists are maintained in the catalogue of gene symbols for wheat (http://wheat.pw.usda.gov/ggpages/pubs.shtml).
Wheat (Triticum aestivum L.) yellow mosaic virus (WYMV) is transmitted by a fungal vector through soil and causes serious wheat yield losses due to yellow mosaic disease, with yellow-streaked leaves and stunted plants. In the present study, the amplified fragment length polymorphisms (AFLP) and simple sequence repeat (SSR) were used to identify the molecular linkages with the resistance gene against WYMV. Bulked segregant analysis was performed with an F2 population derived from the cross of cultivar Ningmai 9 (resistant) × cultivar Yangmai 10 (susceptible). By screening among the resistant or susceptible parents, the F2 pools and the individuals in the F2 population with 64 combined selective AFLP primers (EcoRI/MseI) or 290 reported SSR primers, a polymorphic DNA segment (approximately 120 bp) was amplified using the primer pair E2/M5, and an SSR marker (approximately 180 bp) was located on wheat chromosome 2 A using the primer Xgwm328. Analysis with MAPMAKER/Exp Version 3.0b (Whitehead institute for Biomedical Research, Cambridge, MA, USA) indicated that these two markers were dominantly associated with the resistance gene at distances of 5.4 cM or 17.6 cM, respectively. The resistance gene to WYMV derived from Ningmai 9, is temporarily named YmNM, and was mapped to wheat chromosome 2A.
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Development of wheat (Triticum aestivum L.) cultivars resistant to Wheat streak mosaic virus (WSMV) that remain productive in the absence of the disease would benefit wheat growers. A wheat germplasm (KS93WGRC27) carrying a Thinopyrum intermedium (Host) Barkworth and Dewey chromosome 4Js translocation conferring WSMV resistance was used to develop spring wheat populations segregating for WSMV resistance. Four populations, consisting of a total of 22 translocation-positive (WSMV-resistant), 36 translocationnegative (WSMV-susceptible), and eight parental lines, were grown as a randomized complete block with three replications at Bozeman and Conrad, MT, in 1998 and 1999. Treatments were arranged as a split plot with populations as main plots and progeny and parents as subplots. The agronomic performance of resistant and susceptible lines was compared under inoculated and noninoculated conditions to assess the effectiveness of the WSMV resistance gene and to determine the effects of the Thinopyrum translocation in the absence of disease. A small but significant decrease in yield was observed for noninoculated resistant lines in contrast to susceptible lines. However, the yield range of resistant entries suggests that the recovery of parental yield was possible. The resistance source was highly effective in limiting virus accumulation and yield losses to WSMV, resulting in only a 5% yield reduction in resistant lines under inoculated conditions compared with 32% for susceptible lines. In all instances where WSMV was introduced to field trials, the Thinopyrum translocation provided a significant benefit for resistant lines when compared with susceptible lines. The T. intermedium translocation present in resistant lines had no detrimental effects on end-use quality or other agronomic traits.
Wide crosses in wheat have now been performed for over 100 years. In that time, approximately 100 genes have been transferred for numerous traits, including biotic and abiotic stresses and value-added traits. Resistance genes from alien sources do become defeated with time, so the search for additional variability must continue. Recent screening of alien species has identified accessions with multiple pest resistance plus combinations of pest resistance and value-added traits. The majority of existing induced recombinants are of a noncompensating type with considerable linkage drag, so sequential useage of Ph mutants is recommended to produce smaller interstitial recombinants. Molecular methods, including GISH, RAPD, RFLP, AFLP, and microsatellites, are being widely used to identify integrated alien chromosomes, chromosome segments, and genes.Key words: Triticum aestivium, molecular markers, disease resistance, gene introgression, interspecific hybrids.
Wild grasses, including relatives of wheat, have several desirable characters that can be introduced into both bread wheat and durum wheat. Since current wheat cultivars lack certain traits, for example, resistance to fusarium head blight (scab), related wild grasses may be the only option for useful variability. Wide hybridization of wheat with grasses, coupled with cytogenetic manipulation of the hybrid material, has been instrumental in the genetic improvement of wheat. Chromosome engineering methodologies, based on the manipulation of pairing control mechanisms and induced translocations, have been employed to transfer into wheat specific disease and pest resistance genes from annual (e.g., rye) or perennial (e.g., Thinopyrum spp., Lophopyrum spp., and Agropyron spp.) members of the wheat tribe, Triticeae. The advent of in situ hybridization techniques, for example, fluorescent GISH combined with Giemsa C-banding, has proved immensely useful in characterizing alien chromatin specifying resistance to various pathogens and pests. The use of DNA markers (RAPDs and RFLPs) helps to identify desirable genotypes more precisely and, thereby, facilitates gene transfer into wheat. Such markers may be particularly helpful in monitoring the introgression of alien genes in the wheat genome. In fact, several cultivars, particularly of bread wheat, contain superior traits of alien origin. The development of novel gene-transfer techniques in the past decade that allow direct delivery of DNA into regenerable embryogenic callus of wheat has opened up new avenues of alien-gene transfer into wheat cultivars. Thus, transgenic bread and durum wheats have been produced and methods of gene delivery standardized. The application of transgenic technology has not only yielded herbicide-resistant wheats, but has also helped to improve grain quality by modifying the protein and starch profiles of the grain. These in vitro approaches to gene transfer are developing rapidly, and promise to become an integral part of plant breeding efforts. However, the new biotechnological tools will complement, not replace, conventional plant breeding.Key words: alien-gene transfer, fluorescent GISH, Giemsa banding, homoeologous chromosome pairing, molecular markers, transgenic bread wheat, transgenic durum wheat.
Temperature-sensitive resistance (TSR) that can protect against losses to Wheat streak mosaic virus (WSMV) has been described in elite wheat germplasm. A TSR identified in the advanced breeding line CO960333 and its derivative KS06HW79 was examined in growth-chamber tests conducted under constant temperature regimes of 18, 21, and 24°C against an array of WSMV isolates. At 18°C, all tested isolates systemically infected the pedigree parents, while the progeny line CO960333 remained free of symptoms; at 24°C, all lines were susceptible. At the intermediate temperature of 21°C, the TSR of KS06HW79 was effective in contrast to the TSRs of KS03HW12 and ‘RonL’. In field trials conducted in 2011 and 2012, the TSR expressed in KS06HW79 conferred complete protection against yield losses from inoculation with the Sidney 81 isolate of WSMV, while the TSR of RonL conferred similar protection in 2012 but allowed small losses in 2011. The resistance expressed by KS06HW79 is likely not due to the Wsm1 gene because it did not contain the tightly linked J15 sequence-characterized amplified region (SCAR) DNA marker. These findings suggest that KS06HW79 could be an additional TSR source of value to wheat-breeding programs seeking to control losses from WSMV.
DNA based polymorphism, commonly
known as DNA markers, have extensively been
used for tagging and mapping of simple
inherited trait loci (SITLs) and quantitative trait
loci (QTLs) conferring resistance to biotic and
abiotic stresses in various crop plants. These
tools have also been used for screening of
germplasms, fingerprinting, and marker-assisted breeding (MAB) in crop systems. This
chapter presents an overview on the basic
concepts of marker-assisted breeding of simple
inherited traits, and its most widely used
applications in crop improvement
programmes, viz. marker-assisted backcross
breeding, gene introgression, gene pyramiding
and marker-assisted selection at an early
generation, with emphasis on biotic stress
resistance in several crop plants. In the post-genomic era, the integration the molecular
data with metabolic processes, development
of cost-effective genotypic assay and efficient
breeding strategies will pave the way for the
greater adoption MAB on crop breeding
programmes
Aceria tulipae (Keifer) and Aceria tosichella Keifer (Acari: Eriophyidae) are recorded from Australia, as pests of bulbs and grasses, respectively. Some specimens of A. tosichella occurring on grasses have previously been misidentified as A. tulipae.
In recent years, considerable emphasis has been placed on the development of molecular markers to be used for a variety of objectives. This review attempts to give an account of different molecular markers—restriction fragment length polymorphisms (RFLPs), random amplified polymorphic DNAs (RAPDs), sequence-tagged sites (STS), DNA amplification fingerprinting (DAF), amplified fragment length polymorphisms (AFLPs) and microsatellites (STMS)—currently available for genome mapping and for tagging different traits in wheat. Other markers, including microsatellite-primed polymerase chain reaction (MP-PCR), expressed sequence tags (ESTs) and single nucleotide polymorphisms (SNPs) are also discussed. Recent information on synteny in cereal genomes, marker-assisted selection, marker validation and their relevance to cereal breeding in general and wheat breeding in particular are also examined.
Highly efficient and reproducible micropropagation protocol for Wrightia tomentosa using sexually adult material has been developed. Multiple shoots were induced from nodal shoot segments through forced axillary
branching in vitro. Nature and management of the donor tree, season of collecting explant and their orientation on the medium strongly influenced
the initial establishment of cultures. Explants collected in April–June period and placed vertically on the MS medium containing
2 mgl−1 BAP produced shoots from axillary nodes in vitro. Management of donor tree by serial harvesting of explants every fortnight was necessary to obtain vigorous growth of shoots
in vitro. Explants of the fifth flush (F5) were found most suitable to obtain more than 7 shoots per node on the above medium. The rate of multiplication in subsequent
subcultures was a little more than two and half-fold. Incorporation of phloroglucinol (100 mgl−1) into the multiplication medium containing BAP (2 mgl−1) accelerated the rate of multiplication to 3-fold per subculture. Similar response could be obtained by using 10 mM thidiazuron
(TDZ) alone in the multiplication medium. Nodal segments from in vitro raised shoots were also used to initiate a new culture
cycle. The shoots could be multiplied for at least 24 months without loss of vigor. More than sixty per cent shoots obtained
after sixth subculture developed roots when treated with pre-autoclaved indole-3-butyric acid solution (100 mgl−1) for 10 min and implanted on modified MS medium (major salts reduced to 1/4 strength and 400 mgl−1 activated charcoal). Successfully rooted plants were hardened in vitro in glass bottles containing Soilrite™ irrigated with 1/4 strength MS salt solution (pH 5.0). More than 5,000 plantlets were
successfully hardened in vitro and transferred to greenhouse for acclimatization. The survival rate of the plants during hardening was more than 95 per
cent.
A prerequisite for molecular level genetic studies and breeding in wheat is a molecular marker map detailing its similarities with those of other grass species in the Gramineae family. We have constructed restriction fragment length polymorphism maps of the A-, B-, and D-genome chromosomes of homoeologous group 3 of hexaploid wheat (Triticum aestivum L. em. Thell) using 114 F7-8 lines from a synthetic x bread wheat cross. The map consists of 58 markers spanning 230 cM on chromosome 3A, 62 markers spanning 260 cM on 3B, and 40 markers spanning 171 cM on 3D. Thirteen libraries of genomic or cDNA clones from wheat, barley, and T. tauschii, the wheat D genome donor, are represented, facilitating the alignment and comparison of these maps with maps of other grass species. Twenty-four clones reveal homoeoloci on two of the three genomes and the associated linkages are largely comparable across genomes. A consensus sequence of orthologous loci in grass species genomes is assembled from this map and from existing maps of chromosome-3 homoeologs in barley (Hordeum spp.), T. tauschii, and rice (Oryza spp.). It illustrates the close homoeology among the four species and the partial homoeology of wheat chromosome 3 with oat (Avena spp.) chromosome C. Two orthologous red grain color genes, R3 and R1, are mapped on chromosome arms 3BL and 3DL.
A chromosomal arm map has been developed for common wheat (Triticum aestivum L. em. Thell.) using aneuploid stocks to locate more than 800 restriction fragments corresponding to 210 low-copy DNA clones from barley cDNA, oat cDNA, and wheat genomic libraries. The number of restriction fragments per chromosome arm correlates moderately well with relative DNA content and length of somatic chromosomes. The chromosomal arm locations of loci detected with 6 different clones support an earlier hypothesis for the occurrence of a two-step translocation (4AL to 5AL, 5AL to 7BS, and 7BS to 4AL) in the ancestral wheat genomes. In addition, 1 clone revealed the presence of a 5AL segment translocated to 4AL. Anomalies in aneuploid stocks were also observed and can be explained by intrahomoeologous recombination and polymorphisms among the stocks. We view the development of this chromosomal arm map as a complement to, rather than as a substitute for, a conventional RFLP linkage map in wheat.
A molecular-marker map of bread wheat having many markers in common with other grasses in the Gramineae family is a prerequisite for molecular level genetic studies and breeding in this crop species. We have constructed restriction fragment length polymorphism maps of the A-, B-, and D-genome chromosomes of homoeologous group 2 of hexaploid wheat (Triticum aestivum L. em. Thell) using 114 F7 lines from a synthetic x bread wheat cross and clones from 11 libraries. Chromosomes 2A, 2B, and 2D comprise 57, 60, and 56 markers and each spans about 200 cM. Comparisons between chromosomes are facilitated by 26 sets of homoeoloci. Genes mapped include a heterologous abscisic acid responsive locus cloned as pBS128, the epidermal waxiness inhibitor W21, and two presumed leaf rust and stem rust resistance genes. Anomalies suggesting ancestral rearrangements in chromosome 2B are pointed out and features of wheat group 2 chromosomes that are common to barley (Hordeum vulgare L.), rice (Oryza spp.), and T. tauschii are discussed.
One hundred and seventy-eight loci have been mapped in Triticum tauschii (Coss.) Schmal. (2n = 14, DD) and Triticum aestivum L. em. Thell. (2n = 42, AABBDD). Thirty-five loci were mapped by aneuploid analysis in T. aestivum. One hundred and fifty-two loci, including 143 restriction fragment length polymorphisms (RFLPs), 8 proteins, and 1 leaf rust resistance gene, were mapped in an F2 population (60 plants) of T. tauschii. One hundred and twenty-seven loci were placed in linkage groups belonging to seven D-genome chromosomes of T. tauschii. The source of the probes was a PstI genomic library of T. tauschii, which gave 13% single-low copy clones. Four restriction endonucleases (DraI, EcoRI, EcoRV, HindIII) gave 75% polymorphism between the two parents. Nineteen clones detected multiloci ranging from two to nine in number. Deletions–insertions and point mutations were equally important for generating RFLPs. A hypervariable sequence was identified, which may have potential use in varietal fingerprinting. One...
The chromosome constitutions of eight wheat streak mosaic virus (WSMV)-resistant lines, three of which are also greenbug resistant, derived from wheat/ Agropyron intermedium/Aegilops speltoides crosses were analyzed by C-banding and in situ hybridization. All lines could be traced back to CI15092 in which chromosome 4A is substituted for by an Ag. intermedium chromosome designated 4Ai-2, and the derived lines carry either 4Ai-2 or a part of it. Two (CI17881, CI17886) were 4Ai-2 addition lines. CI17882 and CI17885 were 4Ai-2-(4D) substitution lines. CI17883 was a translocation substitution line with a pair of 6AL.4Ai-2S and a pair of 6AS.4Ai-2L chromosomes substituting for chromosome pairs 4D and 6A of wheat. CI17884 carried a 4DL.4Ai-2S translocation which substituted for chromosome 4D. CI17766 carried a 4AL.4Ai-2S translocation substituting for chromosome 4A. The results show that the 4Ai-2 chromosome is related to homoeologous group 4 and that the resistance gene(s) against WSMV is located on the short arm of 4Ai-2. In addition, CI17882, CI17884, and CI17885 contained Ae. speltoides chromosome 7S substituting for chromosome 7A of wheat. The greenbug resistance gene Gb5 was located on chromosome 7S.
Speed, efficiency, and safety considerations have led many genome mapping projects to evaluate polymerase chain reaction (PCR) sequence amplification as an alternative to Southern blot analysis. However, the availability of informative primer sequences can be a limiting factor in PCR-based mapping. An alternative to random amplified polymorphism detection (RAPD) is the sequence-tagged-site (STS) approach. If informative primer sequences could be derived from known sequences, then current maps, which are based on both known function and anonymous clones, might be easily converted to maps utilizing PCR technology. In this paper, four pairs of primer sequences were obtained from published sequences, and four pairs were obtained by sequencing portions of DNA clones from genomic clones derived from a random genomic library used in the North American Barley Genome Mapping Project (NABGMP). These primers were used to screen for polymorphisms in the progeny of a winter x spring and a spring x spring barley cross. Two types of polymorphisms were distinguished using these primer sets: (1) insertion/deletion events that could be read directly from agarose gels, and (2) point mutation events. The latter were identified using polyacrylamide-gel electrophoresis of PCR products following digestion with restriction endonucleases (four-base cutters). To determine whether the PCR-based polymorphisms were allelic to polymorphisms identified by the clones from which the primer sequences derived, chromosomal assignments and (when possible) co-segregation analysis was performed.
An evaluation was made of the use of random amplified polymorphic DNA (RAPD) as a genetic marker system in wheat. Reproducible amplification products were obtained from varietal, homozygous single chromosome recombinant line and wheat/alien addition line genomic DNA with selected primers and rigorously optimized reaction conditions. Factors influencing the RAPD patterns are DNA concentration, Mg(2+) concentration, polymerase concentration and denaturing temperature. In wheat, the non-homoeologous, non-dose responsive and dominant behaviour of RAPD products devalues their use as genetic markers for the construction of linkage maps, and the high probability that the amplified fragments derive from repetitive DNA limits their use as a source of conventional RFLP probes. However, RAPD markers will most certainly find many applications in the analysis of genotypes where single chromosomes or chromosome segments are to be manipulated.
The polymerase chain reaction (PCR) is an attractive technique for many genome mapping and characterization projects. One PCR approach which has been evaluated involves the use of randomly amplified polymorphic DNA (RAPD). An alternative to RAPDs is the sequence-tagged-site (STS) approach, whereby PCR primers are designed from mapped low-copy-number sequences. In this study, we sequenced and designed primers from 22 wheat RFLP clones in addition to testing 15 primer sets that had been previously used to amplify DNA sequences in the barley genome. Our results indicated that most of the primers amplified sequences that mapped to the expected chromosomes in wheat. Additionally, 9 of 16 primer sets tested revealed polymorphisms among 20 hexaploid wheat genotypes when PCR products were digested with restriction enzymes. These results suggest that the STS-based PCR analysis will be useful for generation of informative molecular markers in hexaploid wheat.
A number of ciliated protozoa are known to read the stop codons UAA and UAG as sense codons that specify glutamine during protein synthesis. In considering evolutionary mechanisms for this curious divergence from the standard genetic code, we propose the existence of progenitor tRNAs for glutamine that can weakly suppress UAA and UAG codons. It has been previously shown that multicopy plasmids that overexpress normal tRNACAAGln and tRNACAGGln genes from the yeast Saccharomyces cerevisiae can partially suppress a number of yeast ochre and amber mutations, respectively. In the present study we show that the tRNACAGGln gene can also function as a weak amber suppressor when expressed in cells at physiological levels. This observation is consistent with a role of tRNACAGGln as an evolutionary progenitor of tRNAs that strongly decode UAG codons.
Genetic variation among wheat ( Triticum aestivum L.) parents is necessary to derive superior progeny from crossing and selection. However, crosses are often performed among elite lines with similar agronomic and end‐use characteristics. Thus, the potential exists for an undesirable narrowing of the germplasm base for any particular class of wheat. The relative genetic diversity within hard red spring wheat was determined in comparison to a sample of wheat accessions representing an array of types and geographic origins. Three groups of accessions were assayed for the frequencies of DNA polymorphism using a total of 38 sequence‐tagged‐site primer sets with polymerase chain reaction. Group 1 contained I0 elite hard red spring wheat cultivars under production in Montana and North Dakota, Group H included 15 hard red spring wheat cultivars and lines from the North American Great Plains, and Group HI contained 20 accessions representing a wide range of collection and morphological types. Twentyfour of 38 primer sets (63%) and 31 of 76 primer‐enzyme combinations (41%) revealed pulymorphisms. The range of genetic similarity estimated by percentage of shared restriction fragments varied from 0.65 to 0.99 among all pairwise comparisons among the 45 lines. Average genetic similarity was 0.81. Genetic similarity among the hard red spring wheats was 0.88, whereas genetic similarity among the broadly based Group HI was 0.78. Our results showed that the breeding pool for hexaploid hard red spring wheat is narrow relative to levels of diversity among and within classes in hexaploid wheat.
We describe the simultaneous amplification of different segments of foreign DNA in transgenic plants using the polymerase
chain reaction (PCR). We used PCR to simultaneously amplify different regions of transformed T-DNA in order to assay the integrity
of transformed constructions in primary tomato transformants. We also used simultaneous PCR amplification to examine the segregation
of transformed sequences in progeny of primary transformants. A tomato transformant containing the maize transposable elementAc was crossed to transformants containing the non-autonomousDs1 element flanked by maizeAdh1 sequences. We then ran PCR reactions on DNA from F1 progeny using two sets of primers, one set homologous toAc and one set homologous toAdh1 sequences on either side ofDs1. Because theAc andAdh1 primers resulted in amplification of fragments of different sizes, it was possible to monitor the inheritance ofAc and theDs1 containingAdh1 genein a single reaction. Additionally, it was possible to identify F1 plants in whichDs1 had excised by the amplification of a fragment the size predicted for an empty donor site. In order to run these reactions,
we have constructed a simple and inexpensive thermal cycler which, when used in conjunction with the rapid miniscreen plant
DNA isolation procedure described, allows the processing of a large number of samples in a single day. Therefore, we have
shown that PCR can be a useful tool to monitor the integrity of foreign genes in transgenic plants, to follow the segregation
of foreign DNA in progeny, and to assay for the excision of transposable elements.
Differences in numbers of wheat curl mites (WCM), Eriophyes tulipae Keifer, infesting wheat cultivars in the field were determined using a new sticky-tape technique. Excised, milk-stage wheat spikes were placed on strips of transparent tape and numbers of mites that crawled out of the drying heads and became stuck on the tape were estimated. 'TAM 107' and 'KS85H22,' both carrying resistance to WCM derived from rye, had significantly lower mite populations in spikes and lower incidence of wheat streak mosaic than other cultivars. Smaller differences in mite numbers in spikes were identified among susceptible cultivars. The sticky-tape procedure provided a simple means of assessing mite numbers in wheat spikes.
Molecular genetic maps are commonly constructed by analyzing the segregation of restriction fragment length polymorphisms
(RFLPs) among the progeny of a sexual cross. Here we describe a new DNA polymorphism assay based on the amplification of random
DNA segments with single primers of arbitrary nucleotide sequence. These polymorphisms, simply detected as DNA segments which
amplify from one parent but not the other, are inherited in a Mendellan fashion and can be used to construct genetic maps
in a variety of species. We suggest that these polymorphisms be called RAPD markers, after Random Amplified Polymorphic DNA.
The chapter discusses on the investigations that are done on mites and the viruses they transmit, the peculiarities of each relationship and become impressed by the opportunities, difficulties, and hence the challenges that remain in this relatively little explored field of virology. Only mites in the families Eriophyidae and Tetranychidae are implicated with plant virus transmission. The mites in both families are specialized for piercing plant cells and sucking their contents, but they differ in many physical and behavioral characteristics. Only 1 Tetranychidae and 5 eriophid mites have been proved to be the vectors of plant viruses. Tetranychus belarius has a wide, nonspecific range of hosts. It also appears to be a nonspecific or casual vector of potato virus Y, which is readily transmitted manually and by aphids, and has a non persistent relationship with both the aphids and the mite vector. In contrast, each of the eriophid mites has a restricted host range, and it is the only vector known for the virus or viruses it transmits. WSMV and RMV are the only eriophid-transmitted viruses that have been also transmitted by artificial sap inoculation. The extremely small size of eriophid mites and the preferences of many for feeding in protected places within buds or in leaf whorls create difficulties in timing inoculation feeds on test plants. It is almost impossible to observe such mites sufficiently closely, while they are feeding, Furthermore, it is difficult to terminate the feeding of mites hidden within buds and leaf whorls, even with the use of miticides, without damaging the plants.
The chromosomes of the B genome of hexaploid wheat (AABBDD) do not pair completely with those of any of the diploid species with genomes similar to B. Various biochemical and molecular analyses have suggested that each of the five diploid species in section Sitopsis of Triticum are ancestral to B. These observations have led to the hypothesis that the B genome may be polyphyletic, descending from more than one diploid ancestor. This hypothesis may account for differences between the wheat B genome and the diploids and also for variability that currently exists among different wheat accessions. In this study, we cloned and compared nucleotide sequences for three low-copy DNA fragments from the B and D genomes of several wheat accessions and from diploid relatives of the B and D genomes. Our results suggested that the amount of DNA sequence variability in wheat is low, although somewhat more variability existed in the B genome than in the D genome. The B genome of wheat was significantly diverged from all the Sitopsis diploid species, and Triticum speltoides was closer to B than to other members of this section. The D genome of wheat was very similar to that of its progenitor, Triticum tauschii. No evidence for a polyphyletic origin of the B genome was found. A more parsimonious hypothesis is that the wheat B genome diverged from its diploid ancestor after the original hybridization event occurred.
The aneuploids of common wheat Res Bull Mo Agric Exp Sta 472 Slykhuis JT (1967) Methods for experimenting with mite trans-mission of plant viruses
- Sears
- Er
Sears ER (1954) The aneuploids of common wheat. Res Bull Mo Agric Exp Sta 472 Slykhuis JT (1967) Methods for experimenting with mite trans-mission of plant viruses. Methods Virol 1 : 347-368
Compendium of wheat diseases DNA polymorphisms amplified by random primers are useful as genetic markers
- Weiss
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- Minnesota Paul
- Jgk Williams
- Kubelik Ark
- Rafalski Ja Livak Jl
- Tingey
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Weiss MV (1987) Compendium of wheat diseases, 2nd edn. APS Press, St. Paul, Minnesota Williams JGK, Kubelik ARK, Livak JL, Rafalski JA, Tingey SV (1990) DNA polymorphisms amplified by random primers are useful as genetic markers. Nuclei Acids Res 18:6531-6535
The aneuploids of common wheat
- Er Sears
Procedures for evaluating wheat streak mosaic virus resistance
- Tj Martin
Compendium of wheat diseases
- Mv Weiss