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SUMMARY: Puccinia striiformis f. sp. tritici (Pst), the causal agent of stripe rust, is a destructive pathogen of Triticum aestivum (wheat), threatening wheat production worldwide. Pst delivers hundreds of effectors to manipulate processes in its hosts during infection. The SGT1 (suppressor of the G2 allele of skp1), RAR1 (required for Mla12 resistance) and HSP90 (heat‐shock protein 90) proteins form a chaperone complex that acts as a core modulator in plant immunity. However, little is known about how Pst effectors target this immune component to suppress plant immunity. Here, we identified a Pst effector PstSIE1 that interacts with TaSGT1 in wheat and is upregulated during the early infection stage. Transient expression of PstSIE1 suppressed cell death in Nicotiana benthamiana induced by VmE02 and PcNLP2. Transgenic expression of PstSIE1‐RNAi constructs in wheat significantly reduced the virulence of Pst. Overexpression of PstSIE1 in wheat increased the number of rust pustules and reduced the accumulation of reactive oxygen species (ROS), indicating that PstSIE1 functions as an important pathogenicity factor in Pst. PstSIE1 was found to compete with TaRAR1 to bind TaSGT1, thus disrupting the formation of the TaRAR1–TaSGT1 subcomplex. Taken together, PstSIE1 is an important Pst effector targeting the immune component TaSGT1 and involved in suppressing wheat defense. Significance Statement: PstSIE1 is an important Pst effector targeting the immune component TaSGT1 and involved in suppressing wheat defense. This work broadens our understanding of how the molecular mechanisms of fungal effectors suppress plant immunity. [ABSTRACT FROM AUTHOR]

Summary: STAUROSPORINE AND TEMPERATURE SENSITIVE3 (STT3) is a catalytic subunit of oligosaccharyltransferase, which is important for asparagine‐linked glycosylation. Sharp eyespot, caused by the necrotrophic fungal pathogen Rhizoctonia cerealis, is a devastating disease of bread wheat. However, the molecular mechanisms underlying wheat defense against R. cerealis are still largely unclear. In this study, we identified TaSTT3a and TaSTT3b, two STT3 subunit genes from wheat and reported their functional roles in wheat defense against R. cerealis and increasing grain weight. The transcript abundance of TaSTT3b‐2B was associated with the degree of wheat resistance to R. cerealis and induced by both R. cerealis and exogenous jasmonic acid (JA). Overexpression of TaSTT3b‐2B significantly enhanced resistance to R. cerealis, grain weight, and JA content in transgenic wheat subjected to R. cerealis stress, while silencing of TaSTT3b‐2B compromised resistance of wheat to R. cerealis. Transcriptomic analysis showed that TaSTT3b‐2B affected the expression of a series of defense‐related genes and JA biosynthesis–related genes, as well as genes coding starch synthase and sucrose synthase. Application of exogenous JA elevated expression levels of the abovementioned defense‐ and grain weight–related genes, and rescuing the resistance of TaSTT3b‐2B–silenced wheat to R. cerealis, while pretreatment with sodium diethyldithiocarbamate, an inhibitor of JA synthesis, attenuated the TaSTT3b‐2B–mediated resistance to R. cerealis, suggesting that TaSTT3b‐2B played critical roles in regulating R. cerealis resistance and grain weight via JA biosynthesis. Altogether, this study reveals new functional roles of TaSTT3b‐2B in regulating plant innate immunity and grain weight, and illustrates its potential application value for wheat molecular breeding. [ABSTRACT FROM AUTHOR]

Iranian wheat landrace accessions (IWAs) were collected from country‐wide farm fields and market places in 1935 by a professor at the University of Tehran and shared with University of California at Davis, California. IWAs were further submitted to the genebank of International Maize and Wheat Improvement Center (CIMMYT), Mexico. 2,403 IWAs from CIMMYT's genebank were assayed by DArT‐seq technology to assess genetic diversity. No apparent ecogeographic patterns related to genetic diversity were detected, probably due to long‐term transport and frequent interchange of landraces among farmers. A multivariate clustering procedure combining genotypic and phenotypic information was used in selecting a core‐set, which represented 15% of the hexaploid wheat accessions included in this study. This subset captured an estimated 93% of rare (frequency <0.05) alleles. Multisite phenotypic data (India, Mexico) validated the ability of the core‐set in detecting useful variants. Potential donor accessions for multiple traits (disease resistance, zinc concentration) were identified from the core‐set for wheat‐breeding. This report illustrates a breeder friendly robust core‐set formulation strategy for harnessing the useful genetic variation stored in the genebanks. [ABSTRACT FROM AUTHOR]

Blast disease, caused by the Magnaporthe oryzae Triticum pathotype (MoT), is a major concern for wheat production in tropical and subtropical regions. The most destructive symptoms occur in wheat spikes. Infected spikes become bleached due to partial or total sterility, producing small and wrinkled grains. High disease pressure of the disease results in significant yield losses. This study aimed to identify wheat quantitative trait loci (QTLs) conferring resistance to blast disease at the heading stage. A doubled‐haploid population was developed from the cross between BRS 209 (susceptible) and CBFusarium ENT014 (resistant, carrying the 2NS translocation). A linkage map was constructed containing 5,381 molecular markers and the inclusive composite interval mapping method was employed for QTL detection. Four QTLs were mapped in response to two MoT isolates. The major QTL identified on the 2AS chromosome explained an average of 84.0% of the phenotypic variation for spike bleaching at 9 days postinoculation and reinforces the potency of the 2NS translocation. Recombination between the distal region of chromosome 2AS and the 2NS marker was found. These results could explain why some lines carrying the VENTRIUP/LN2 marker have a variable reaction to the disease. QTLs on 5B and 7B chromosomes were also identified. Two mechanisms of resistance were hypothesized: the hypersensitive response and resistance to colonization of host tissues. The KASP markers thus developed and simple sequence repeats (SSRs) allocated in QTL regions can be used in the future for the development of wheat blast‐resistant cultivars. [ABSTRACT FROM AUTHOR]

Summary: Sequence elimination is one of the main mechanisms that increases the divergence among homoeologous chromosomes after allopolyploidization to enhance the stability of recently established lineages, but it can cause a loss of some economically important genes. Synthetic hexaploid wheat (SHW) is an important source of genetic variation to the natural hexaploid wheat (NHW) genepool that has low genetic diversity. Here, we investigated the change between SHW and NHW genomes by utilizing a large germplasm set of primary synthetics and synthetic derivatives. Reproducible segment elimination (RSE) was declared if a large chromosomal chunk (>5 cM) produced no aligned reads in more than five SHWs. RSE in five genomic regions was the major source of variation between SHW and NHW. One RSE eliminated almost the complete short arm of chromosome 1B, which contains major genes for flour quality, disease resistance and different enzymes. The occurrence of RSE was highly dependent on the choice of diploid and tetraploid parental lines, their ancestral subpopulation and admixture, e.g. SHWs derived from Triticum dicoccon or from one of two Aegilops tauschii subpopulations were almost free of RSE, while highly admixed parents had higher RSE rates. The rate of RSE in synthetic derivatives was almost double that in primary synthetics. Genome‐wide association analysis detected four loci with minor effects on the occurrence of RSE, indicating that both parental lines and genetic factors were affecting the occurrence of RSE. Therefore, pre‐pre‐breeding strategies should be applied before introducing SHW into pre‐breeding programs to ensure genomic stability and avoid undesirable gene loss. Significance Statement: This study documented the occurrence of multiple reproducible sequence eliminations in synthetic hexaploid wheat compared with natural hexaploid wheat; a phenomenon affected by the choice of parental lines, their admixture and genetic factors. These sequence eliminations caused significant gene loss and could affect the fertility of the progeny of natural/synthetic hexaploid hybrids, therefor it is important to avoid these in practical breeding programs. [ABSTRACT FROM AUTHOR]

The actin cytoskeleton is involved in plant defense responses; however, the role of the actin-depolymerizing factor (ADF) family, which regulates actin cytoskeletal dynamics, in plant disease resistance, is largely unknown. Here, we characterized a wheat ( Triticum aestivum) ADF gene, TaADF7, with three copies located on chromosomes 1A, 1B, and 1D, respectively. All three copies encoded the same protein, although there were variations in 19 nucleotide positions in the open reading frame. Transcriptional expression of the three TaADF7 copies were all sharply elevated in response to avirulent Puccinia striiformis f. sp. tritici ( Pst) infection, with similar expression patterns. TaADF7 regulated the actin cytoskeletal dynamics by targeting the actin cytoskeleton to execute actin binding/severing activities. When the TaADF7 copies were all silenced by virus-induced gene silencing, the growth of Pst hypha increased and sporadic urediniospores were observed, as compared with control plants, upon inoculation with avirulent Pst. In addition, the accumulation of reactive oxygen species (ROS) and the hypersensitive response (HR) were greatly weakened, whereas cytochalasin B partially rescued the HR in TaADF7 knock-down plants. Together, these findings suggest that TaADF7 is likely to contribute to wheat resistance against Pst infection by modulating the actin cytoskeletal dynamics to influence ROS accumulation and the HR. [ABSTRACT FROM AUTHOR]

The improvement of wheat through breeding has relied strongly on the use of genetic material from related wild and domesticated grass species. The 1 RS chromosome arm from rye was introgressed into wheat and crossed into many wheat lines, as it improves yield and fungal disease resistance. Pm8 is a powdery mildew resistance gene on 1 RS which, after widespread agricultural cultivation, is now widely overcome by adapted mildew races. Here we show by homology-based cloning and subsequent physical and genetic mapping that Pm8 is the rye orthologue of the Pm3 allelic series of mildew resistance genes in wheat. The cloned gene was functionally validated as Pm8 by transient, single-cell expression analysis and stable transformation. Sequence analysis revealed a complex mosaic of ancient haplotypes among Pm3- and Pm8-like genes from different members of the Triticeae. These results show that the two genes have evolved independently after the divergence of the species 7.5 million years ago and kept their function in mildew resistance. During this long time span the co-evolving pathogens have not overcome these genes, which is in strong contrast to the breakdown of Pm8 resistance since its introduction into commercial wheat 70 years ago. Sequence comparison revealed that evolutionary pressure acted on the same subdomains and sequence features of the two orthologous genes. This suggests that they recognize directly or indirectly the same pathogen effectors that have been conserved in the powdery mildews of wheat and rye. [ABSTRACT FROM AUTHOR]

By carefully separating type I and type II resistances, the possible effects of plant height on fusarium head blight (FHB) resistance in wheat were assessed using near-isogenic lines (NILs) for several different reduced-height ( Rht) genes. Tall isolines all gave better type I resistance than their respective dwarf counterparts when assessed at their natural heights. These differences largely disappeared when the dwarf isolines were physically raised so that their spikes were positioned at the same height as those of their respective tall counterparts. The effects of plant height on type II resistance was less clear. For those NIL pairs which showed significant differences, it was the dwarf isolines which gave better resistance. As the Rht genes involved in these NILs locate at different genomic regions, the differences in FHB between the dwarf and tall isolines are unlikely to be the result of linkages between each of the different Rht loci with a beneficial or a deleterious gene affecting type I or type II resistance. Rather, the different FHB resistances are probably caused by direct or indirect effects of height difference per se, and microclimate may have contributed to the better type I resistance of the tall plants. Thus, caution should be exercised when attempting to exploit any of the FHB resistant loci co-located with Rht genes. [ABSTRACT FROM AUTHOR]

With 2 figures and 1 table Fungal diseases of wheat, including powdery mildew (Pm), have caused significant crop, yield and quality losses throughout the world and continue to impact on production. Knowledge of the genetic basis of powdery mildew resistance of wheat cultivars will greatly support future efforts developing and cultivating resistant cultivars. Genetic studies were conducted on the German winter wheat cultivar 'Cortez' to identify genes involved in powdery mildew resistance at seedling and adult plant growth stages using doubled haploid (DH) population Atlantis/Cortez. Analysis of association between molecular markers and powdery mildew severity in selected genotypes indicated the involvement of two genes on chromosomes 1A and 7B in seedling resistance. The same gene on chromosome 1A was also found to be effective at adult plant stage. Quantitative trait loci analysis corroborated that the gene on chromosome 1A significantly contributed to field resistance in all five test environments and explained between 22.9% and 51.4% of the total phenotypic variation. The gene on chromosome 7B was identified as Pm5, whereas the gene on chromosome 1A potentially conditioning resistance was identified as Pm3e. [ABSTRACT FROM AUTHOR]

With 2 figures and 2 tables Two greenbug resistance genes Gb2 and Gb6 derived from the same donor rye line 'Insave', are present in wheat germplasm lines 'Amigo' and 'GRS1201', respectively as 1AL.1RS wheat-rye translocations. The allelic relationship between the two genes has not been determined, and no molecular markers for Gb6 are available. In this study, molecular mapping of Gb2 and Gb6 was performed in a mapping population derived from a cross between 'N96L9970' ( Gb6Gb6) and 'TAM 107' ( Gb2Gb2). Segregation among F2:3 families of host responses to infestation of greenbug biotypes E and KS-1 revealed that Gb2 and Gb6 were different linked loci in 1RS. Gb2 and Gb6 were 15.8 cM apart with Gb6 being distal to Gb2. Despite the low number of marker polymorphisms between the parental lines, eight markers linked with Gb2 and Gb6 were identified. The closest marker, XIA294, was 11.4 cM proximal to Gb2. Deletion mapping indicated that both Gb2 and Gb6 were physically located in the satellite region of 1RS. [ABSTRACT FROM AUTHOR]

With 3 figures and 3 tables Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is one of the most devastating diseases in common wheat ( Triticum aestivum L.). With the objective of identifying and tagging a new gene for resistance to stripe rust in wheat line P81, F1, F2 and F2:3 populations from the cross ‘Chuanmai 28’/P81 were inoculated with Chinese PST race CYR32 in greenhouse and field trials. P81 carried a single dominant gene for resistance (designated YrP81) to CYR32. Tests of allelism showed that YrP81 was different from Yr5, Yr10, Yr15 and Yr26. Simple sequence repeat (SSR) and resistance gene-analogue polymorphism (RGAP) between the parents were used for genotyping the F2 populations. YrP81 was closely linked to four SSR loci on chromosome 2BS with genetic distances of 18.3 cM ( Xwmc25), 1.8 cM ( Xgwm429), 4.1 cM ( Xwmc770) and 5.3 cM ( Xgwm148). Two RGAP markers RGA1 (NLRR/XLRR) and RGA2 (Pto kin4/NLRR-INV2) were also closely linked to YrP81 with genetic distances of 4.7 and 6.3 cM, respectively. The linkage map of YrP81 and molecular markers was established in the order Xwmc25- RGA2- RGA1- Xgwm429- YrP81- Xwmc770- Xgwm148. Pedigree analysis, response patterns with Chinese PST races and associations with markers suggested that YrP81 is a novel stripe rust resistance gene. The PCR-based microsatellite and RGAP markers identified here could be applied in selection of YrP81 in wheat breeding. [ABSTRACT FROM AUTHOR]

This study reports the discovery of a gene for resistance to septoria tritici blotch (STB) in two spring wheat cultivars, Courtot and Tonic. The gene, named Stb9, confers resistance to Mycosphaerella graminicola isolate IPO89011. It was mapped by quantitative trait loci (QTL) analysis using an existing map of Courtot × Chinese Spring and was located between markers Xfbb226 (3·6 cM) and XksuF1b (9 cM) on the long arm of chromosome 2B. Markers linked to Stb9 in Courtot were then shown to be linked to resistance to IPO89011 in F3 families of Tonic × Longbow. Allelism tests in which Tonic was crossed with Courtot confirmed that Tonic has a gene for resistance to IPO89011 at or very close to the Stb9 locus. SSR markers flanking Stb9 may be used in marker-assisted selection to introgress this gene into winter cultivars or in spring wheat breeding programmes outside Europe. [ABSTRACT FROM AUTHOR]

Wheat stem rust samples were collected in 2006 and 2007 in the Arsi, Bale, Shewa and northwest regions of Ethiopia to determine virulence diversity and race distribution in Puccinia graminis f.sp. tritici populations. Stem rust incidence was high in Arsi, Bale and east Shewa. In northwest Ethiopia, and north and west Shewa, stem rust was prevalent at low levels. A total of 152 isolates was analysed and 22 races were identified. Races TTKSR (Ug99), TTHSR and RRTTR were predominant, with frequencies of 26·6, 17·7 and 11·1%, respectively. These races were also detected in all regions. The highly virulent race designated Ug99 was present throughout the country and dominated in all regions except northwest Ethiopia. A variant of Ug99 virulent against the stem rust resistance gene Sr24 was not detected in this study. Four stem rust resistance genes ( Sr13, Sr30, Sr36 and SrTmp) were found to confer resistance to most of the races prevalent in Ethiopia. With the exception of Sr30, which is not effective against Ug99, these genes could be used in breeding for resistance to stem rust in Ethiopia. [ABSTRACT FROM AUTHOR]

This work presents a global investigation of total fatty acid (FA) content in wheat in relation to treatment with four inducers of resistance and to powdery mildew infection. Linolenic acid (C18:3), linoleic acid (C18:2) and palmitic acid (16:0) were the most abundant FAs in wheat leaves. We investigated the effect of the following inducers of resistance: Iodus40, heptanoyl salicylic acid (HSA), Milsana and trehalose on FA accumulation. Previous studies established that lipid metabolism is altered by these compounds, and we therefore aimed to characterise their impact at the FA level. During a time course experiment, content (quantitative analysis) and percentage (qualitative analysis) of FAs were compared in treated plants and in controls, as well as in plants inoculated with Blumeria graminis f. sp. tritici (i) and non-inoculated (ni) plants. No change in C18:3 content was observed. C18:1 in Iodus 40-treated (ni) plants showed a quantitative 1.2-fold increase. Lauric acid (C12:0) content quantitatively increased after Iodus 40 (2.8-fold), Milsana (4.8-fold) and trehalose (4.0-fold) treatment in (i) plants. However, eicosadienoic acid (C20:2) quantitatively decreased in (ni) plants after Iodus 40 (1.5-fold) and Milsana (2.3-fold) treatment. The amount of C18:2 increased (1.6-fold) after HSA treatment in (i) plants. All these variations in FA content were correlated with variations in the corresponding relative percentages. Our work provides the first evidence for alterations in C12:0, C18:1, C18:2 and C20:2 FA content caused by four resistance inducers. We also compared the amount and percentage of each FA in untreated (i) and (ni) plants. In (i) plants, eicosadienoic acid (C20:2) increased and C18:2 decreased slightly. The potential involvement of these FAs during induced resistance and infection is discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Spot blotch, caused by Cochliobolus sativus, is considered one of the most destructive diseases of wheat ( Triticum aestivum) in the warm areas of South Asia. Over the past 20 years, wheat breeding efforts in the region have improved spot blotch resistance in susceptible commercial cultivars. This study assessed resistance and spot blotch-induced yield losses in newly released wheat cultivars developed in Bangladesh since the release of the landmark wheat variety ‘Kanchan’. Replicated field studies were conducted during the 2003 and 2004 wheat seasons at two sites: a farmer's field and a research station in a warm region of Bangladesh where spot blotch has been a serious problem. Spot blotch affected 60% of the crop and caused yield losses of from 2% to 22%. Disease severity and disease-induced grain yield reductions were less in wheat genotypes developed since 1983, with a corresponding trend towards higher yield in newly developed varieties. The level of resistance to spot blotch in the new cultivars and advanced breeding lines represents considerable progress in breeding for resistance over the past two decades. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) is a devastating disease that reduces the yield, quality and economic value of wheat. For quantitative trait loci (QTL) analysis of resistance to FHB, F3 plants and F3:5 lines, derived from a ‘Wangshuibai’ (resistant)/‘Seri82’ (susceptible) cross, were spray inoculated during 2001 and 2002, respectively. Artificial inoculation was carried out under field conditions. Of 420 markers, 258 amplified fragment length polymorphism and 39 simple sequence repeat (SSR) markers were mapped and yielded 44 linkage groups covering a total genetic distance of 2554 cM. QTL analysis was based on the constructed linkage map and area under the disease progress curve. The analyses revealed a QTL in the map interval Xgwm533–Xs18/m12 on chromosome 3BS accounting for up to 17% of the phenotypic variation. In addition, a QTL was detected in the map interval Xgwm539–Xs15/m24 on chromosome 2DL explaining up to 11% of the phenotypic variation. The QTL alleles originated from ‘Wangshuibai’ and were tagged with SSR markers. Using these SSR markers would facilitate marker-assisted selection to improve FHB resistance in wheat. [ABSTRACT FROM AUTHOR]

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko) has caused serious reduction in wheat production in 17 Western states of the United States since 1986. Inheritance of resistance to RWA in seven wheat lines and the allelism of the resistance genes in these lines with three known resistance genes Dn4, Dn5, and Dn6 were studied. The seven resistant lines were crossed to a susceptible wheat cultivar 'Carson' and three resistant wheats: CORWA1 (Dn4), PI 294994 (Dh5), and PI 243781 (Dn6), Seedlings of the parents, F[sub1], and F[sub2] were screened for RWA resistance in the greenhouse by artificial infestation. Seedling reactions were evaluated 21-28 days after the infestation using a 1-9 scale. The resistance level of all the F [sub1] hybrids was similar to that of the resistant parent, indicating dominant gene control, Only two distinctive classes were present and no intermediate types were observed in the F[sub2] population, suggesting qualitative, nonadditive gene action, in which the presence of any one of the dominant alleles confers complete resistance to RWA. Resistance in CI 2401 is controlled by two dominant genes. Resistance in C16501 and PI 94365 is governed by one dominant gene. Resistance in PI 94355 and PI 151918 may be conditioned by either one dominant gene or one dominant and one recessive gene. No conclusion can be made on how many resistance genes are in AUSVA1-F[sub3], since the parent population was not a pure line. Allelic analyses showed that one of resistance genes in CI 2401 and PI 151918 was the same allele as Dn4. the resistance gene in CI 6501 was the same allele as Dn6, and AUS-VA1-F[sub3] had one resistance gene which was the same allele as one of the resistance genes in PI 294994. One non-allelic resistance gene different from the Dn4, Dh5, and Dh6 genes in CI 2401. P1 94355, PI 94365, and PI 222668 was identified and should be very useful in diversifying gene sources in wheat breeding. [ABSTRACT FROM AUTHOR]

A synthetic hexaploid, Triticum timofeevii × T. tauschii, was used to transfer disease resistance genes to the commercial cultivar Saratovskaya 29 (S29) by backcrossing. After five backcrosses the resulting derivatives still showed some traits of the synthetic, namely brown spike glumes and several gliadin components. Genetic analysis showed that the derived forms had inherited the Gli-D1 allele of the synthetic, which was found to be tightly linked to a gene for glume colour, Recombination percentages between these genes was estimated to be 2.5 ± 1.7%. The development of the derivatives was also accompanied by a rearrangement within the Gli-B1 locus, resulting in the formation of a new variant of the allele in S29. [ABSTRACT FROM AUTHOR]

Among the wheatgrasses that are possible sources of genetic resistance for wheat to barley yellow-dwarf-virus disease (BYD) are those that have been commonly subsumed under the name Agropyron elongatum (Host) P. Beauv. Two of these wheatgrass species are the diploid Lophopyrum elongatum (Host) Á. Löve (2n = 2x = 14) and the decaploid L. ponticum (Podp.) Á. Löve (2n = 10x = 70). These two species, the addition and substitution lines of L. elongatum chromosomes in hexaploid wheat (Triticum aestivum L.), and derivatives of hybrids between hexaploid wheat and L. ponticum, were screened for resistance to BYD, as defined by visual symptoms in field-grown plants. The two species, an amphiploid derived from L. elongatum × 'Chinese Spring' wheat, and the derivatives involving L. ponticum chromosomes were all highly resistant. The substitution and addition lines of L. elongatum chromosomes in 'Chinese Spring' revealed that the genetic control of resistance in L. elongatum must be complex, with more than one critical locus involved. Chromosomes 2E and 5E are involved and there are lesser contributions to resistance from the remaining wheatgrass chromosomes. One highly resistant derivative was determined to have only three pairs of L. ponticum chromosomes. It has a wheat-like morphology and shows promise for further characterization. [ABSTRACT FROM AUTHOR]

A total of 20 cultivars of winter wheat were tested by ELISA for resistance to Pseudocercosporella herpotrichoides in six environments and three growth stages. In a three-factor statistical analysis, the contribution of the different factors to their respective interactions was studied. The genotype x environment interactions exerted a considerable influence which could be reduced by increasing the number of test locations. Environments with a high disease level were less suited to measuring resistance than those environments with a medium level. Estimates of heritability from 0.54 to 0.78 show that successful selection may be possible using ELISA. Significant correlations of quantative resistance at different environments were only obtained under similar environmental conditions (the same location, the same year) and with P herpotrichoides populations of similar composition (the same inoculum). The contributions of the individual cultivars to the genotype environment interactions were not significantly different, except for 'Roazon' and 'Rendezwms'. Due to high environmental effects in growth stage 85, the determination of quantitative resistance was more reliable n younger stages (65. 75). Nevertheless the use of the values from that late stage did not reduce the genetic parameters (σ[SUP2], h[SUP2]) if they were combined with the earlier measurements. [ABSTRACT FROM AUTHOR]

Resistance to Pseudocercosporella herpotrichoides in five wheat cultivars, accession W6 7283 of Dasypyrum villosum, and Chinese Spring disomic addition lines of the D, villosum chromosomes 1V, 2V, 4V, 5V, 6V and 7V, was evaluated in seedlings by measuring disease progress 6 weeks after inoculation with a figlucuronidase-transformed strain of the pathogen and by visual estimates of disease severity. D, villosum and the disomic addition line of chromosome 4V were as resistant as wheat cultivars 'VPM-1 ' and 'Cappelle I)esprez', but less resistant than 'Rendezvous'. Resistance of the chromosome 4V disomic addition line was equivalent to that of D. villosum. 'Chinese Spring' and disomic addition lines of 1V, 2V, 5V, 6V and 7V were all susceptible, These results confirm SPRAGUF's (1936) report of resistance in D. villosum to P. herpotrichoides and establish the chromosomal location for the genes controlling resistance. The presence of chromosome 4V in the addition line and its homoeology to chromosome 4 in wheat were confirmed by Southern analysis of genomic DNA using chromosome group 4-specific clones. This genetic locus is not homoeologous with other known genes for resistance to P. herpotrichoides located on chromosome group 7, and thus represents a new source of resistance to this pathogen. [ABSTRACT FROM AUTHOR]

Wheat-barley addition lines 7H, 21-1, 3H, 4H, 6H and 5H having barley chromosomes 1, 2, 3, 4, 6 and 7, respectively, were evaluated for resistance to karnal bunt (Neovossia indica) using syringe inoculation of sporidial suspensions of N. indica under glass-house conditions. Addition lines 4H and 7H were rated as highly resistant and resistant, respectively, with zero and 3.22 coefficients of infection compared to 'Chinese Spring' which had a 23.5 coefficient of infection. All the six addition lines were found to be susceptible to specific virulences of Puccama recondita tritici and P. striiform:s. [ABSTRACT FROM AUTHOR]

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko) is one of the most destructive insect pests of cereals world‐wide. Although resistant cultivars have been bred, the biochemical mechanism of resistance is unknown. The aim of this work was to gain information on the mechanism of resistance which could contribute to more directed breeding of resistant cultivars in the future. The effect of RWA infestation on the inter‐ and intracellular β‐1,3‐glucanase activities was studied in different resistant wheat (Triticum aestivum L.) cultivars containing the Dn‐1 gene for RWA resistance and corresponding near‐isogenic susceptible cultivars. The activity was determined spectrophotometrically by measuring the release of glucose from laminarin. Infestation differentially induced the intra‐ and intercellular activities to much higher levels in resistant than susceptible cultivars within 48 h. According to immunological studies induced enzyme activities were due to increased protein levels. The intracellular β‐1,3‐glucanase contained about 8% exo‐activity. The exo‐activity made an insignificant contribution to the intercellular activity. The genetic background into which the resistance gene was bred did affect the level of activity that corresponded to the resistance performance. Seven apoplastic isoforms of β‐1,3‐glucanase, varying from acidic to basic, were resolved by isoelectric focusing. All isoenzymes were equally induced and no specific one could be linked to resistance or susceptibility. The RWA induced β‐1,3‐glucanase activity in resistant cultivars closely resembles defence responses during pathogenesis and seems to be part of a general defence response like the hypersensitive reaction (HR), which confers resistance to the RWA. This knowledge might be helpful in future to identify genes for RWA resistance. The increased β‐1,3‐glucanase activity after RWA infestation might serve as an additional measure to biochemically trace resistance in crosses during breeding. [ABSTRACT FROM AUTHOR]

A study was conducted under controlled environment conditions in a phytotron to determine the nature of the inheritance of resistance Helminthosporium leaf blight (HLB) in a synthetic hexaploid wheat line, ‘Chirya-3’, against the isolate KL-8 of Bipolaris sorokiniana from the major wheat growing region of India. Crosses were made between two susceptible lines ‘WH 147’ and ‘Chinese Spring’. Analyses of F1 and F2 populations of these two crosses (‘WH 147’ × ‘Chirya-3’ and ‘Chinese Spring’ × ‘Chirya-3’) showed that resistance against the isolate in ‘Chirya-3’ was governed by two recessive genes functioning in a complementary interaction giving an F2 segregation pattern of 1 : 15 (resistant : susceptible). The segregation pattern of the resistant F2 progenies in F3 families from both crosses confirmed that two homozygous recessive genes were responsible for resistance to the isolate of Bipolaris sorokiniana in the synthetic line ‘Chirya-3’. It is proposed that the genes be designated as hlbr1 and hlbr2. [ABSTRACT FROM AUTHOR]

Twenty-one bread-wheat entries were selected after careful screening for complete or near-complete resistance to yellow rust (Puccinia striiformis), stem rust (P. graminis), and leaf rust (P. recondita). In 1987, the 21 entries were intercrossed in a near-half diallel scheme. The resulting 190 F[sub2] populations were advanced to F[sub7] under selection for complete resistance to the three rusts and for good agronomic types. In 1992 the 21 parents and 140 selected F[sub7] lines were assessed for their resistance to the three rusts. Of the 21 parents, 12 showed a breakdown of yellow rust resistance, five a breakdown of stem rust resistance and two a breakdown of leaf rust resistance. In addition, several of the 140 selected F[sub7] lines, all still resistant in F[sub6], had become susceptible to one or more of the rusts. It appears that a progression towards more complex races, especially of yellow rust, is inevitable for the wheat-cereal rust pathosystems when the selection is for complete or near-complete resistance. [ABSTRACT FROM AUTHOR]

Inheritance of resistance to Karnal bunt was investigated in the crosses of four resistant synthetic hexaploid wheats (SH; Triticum turgidum × T. tauschii) and two susceptible T. aestivum cultivars. The resistance was dominant or partly dominant over susceptibility. The SH cultivars Chen/T. tauschii (205) and Chen/T. tauschii (224) have single dominant resistance genes which could be allelic to each other 'Altar 84'/ T. tauschii(219) appeared to have two dominant genes for resistance. 'Duergand' T. tauschii (214) possessed two complementary dominant genes for resistance. The work is being extended to involve diverse Karnal bunt-resistant SH and bread wheat cultivars. [ABSTRACT FROM AUTHOR]