A note on resistance to Hessian fly (Mayetiola destructor) [Diptera : Cecidomyidae] biotype L in tribe Triticeae

Quarante et une accessions de blés primitifs et indigènes (Triticum spp.), 16 accessions du genre Aegilops et 20 accessions ou cultivars du genre Agropyron ont été évaluées pour la première fois pour leur réaction au biotype L de la mouche de Hesse (Mayetiola destructor). Trois accessions du Triticum monococcum, 13 accessions du genre Aegilops et 13 accessions ou cultivars du genre Agropyron ont été trouvées résistantes de façon homogène. L'antibiose s'est manifestée dans certains cas mais dans certains autres, il est apparu une résistance physique attribuable à la présence de la pubescence foliaire ou de la ligule. La pubescence du Triticum boeoticum n'a pas été efficace afin de procurer de la résistance.Forty-one accessions of primitive and wild wheats (Triticum species), 16 accessions of Aegilops species, and 20 accessions or cultivars of Agropyron species were evaluated for the first time for reaction to biotype L of Hessian fly (Mayetiola destructor). Three accessions of Triticum monococcum, 13 accessions of Aegilops species, and 13 accessions or cultivars of Agropyron species were found homogeneously resistant. Antibiosis was operative in some cases but in others there appeared to be physical resistance due to the presence of leaf pubescence or ligule. Pubescence of Triticum boeoticum was not effective in providing resistance

Genetics of resistance to Hessian fly (Mayetiola destructor) [Diptera : Cecidomyiida] biotype L in diploid wheat

La mouche de Hesse est un important ravageur de blé (Triticum spp.) et le biotype L de cette mouche est reconnu comme le plus virulent des biotypes connus. L'héritabilité de la résistance au biotype L de la mouche de Hesse a été étudiée à l'aide de croisements entre, d'une part, une lignée résistante de Triticum monococcum et, d'autre part, deux lignées sensibles de T. monococcum et une lignée sensible de T. boeoticum, tous des blés diploïdes. Les familles de plante F2 ou issues de rétrocroisements ont été évaluées au stade de semis par leur réaction à la mouche de Hesse et les ratios de ségrégation génétique des familles résistantes ou ségréguées par rapport aux familles sensibles ont été analysés par des tests d'ajustement du chi-carré. Il a été découvert que l'héritabilité est simple et sous le contrôle d'un ou deux gènes. Ceci est la première mention de l'héritabilité de la résistance à la mouche de Hesse chez les blés diploïdes de génome A et son contrôle génétique simple suggère la possibilité de transférer ce caractère aux blés cultivés.Hessian fly (Mayetiola destructor) is a serious pest of wheat (Triticum spp.) and of the reported biotypes of Hessian fly, biotype L is described as the most virulent. Inheritance of resistance to Hessian fly biotype L was investigated in crosses of a resistant accession of Triticum monococcum, and two susceptible accessions of T. monococcum and one susceptible accession of T. boeoticum, all diploid wheats. F2 and testeross (backeross) families were classified for reaction to Hessian fly in the seedling stage and analysed by Chi-square goodness-of-fit tests for genetic segregation ratios of resistant or segregating families to susceptible families. Resistance was found to be simply inherited, controlled by one or two genes. This is the first report on the inheritance of resistance to Hessian fly in A-genome diploid wheats, and simple genetic control indicates possibility of transfer of this trait to cultivated wheats

Inheritance and mapping of stem rust resistance of wheat line PI 410966

Stem rust caused by Puccinia graminis f. sp tritici of wheat (Triticum aestivum L.) is one of the most destructive cereal diseases globally. Concern about the disease has increased since 1999 with the discovery in Uganda of a new virulent race of Pgt, designated as race TTKSK (also known as Ug99). The objectives of this experiment were to characterize the resistance and to determine the chromosomal location of the stem rust resistance in the spring wheat line PI 410966. A mapping population was developed from a cross between PI 410966 and a susceptible wheat line OK3040. An inoculation test with isolate 04KEN156/04 of race TTKSK was conducted at the USDA-ARS Cereal Disease Laboratory in the F6:7 generation, and the F6:7 phenotypic data were used to genetically map the resistance gene to the centromeric region on chromosome 2BS. The single locus explained the observed F6:7 resistant and susceptible scores. The location of the gene and molecular marker banding profiles of the diagnostic markers suggest that the stem rust resistance gene in PI 410966 could be a new gene, an allele of Sr36, or Sr36

Genetic, abiotic and social influences on sex differentiation in cichlid fishes and the evolution of sequential hermaphroditism

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73799/1/j.1467-2979.2005.00184.x.pd

Novel germplasm providing resistance to barley yellow dwarf virus in wheat

The lack of suitable genes in existing wheat germplasm collections makes breeding for specific traits a difficult task. Although tolerance to barley yellow dwarf viruses (BYDV) has been reported in wheat accessions, there are no suitable levels of resistance to BYDV, so genes are sought from wild relatives. The ability for Thinopyrum species to inhibit replication of BYDV makes them attractive sources of resistance for germplasm development. Breeding programs are exploiting Thinopyrum species to develop wheat germplasm resistant to BYDV. The transfer of genes from Thinopyrum into wheat by wide crossing and selecting progeny using molecular markers identified suitable material to some strains of BYDV. The implementation of molecular marker technology has been useful for rapid selection of wheat lines with resistance to some strains of BYDV in a breeding program. However, it is now clear that Thinopyrum species contain a number of resistance genes on different genomes and homoeologous chromosomes. In order to achieve broad-spectrum resistance to the various serotypes of the BYDV complex it will be best to combine a number of these genes. Research efforts are now focussed on introgressing other genes from Thinopyrum into wheat that provide resistance to several additional strains of BYDV. Molecular markers will play an important role during selection in pyramiding genes to develop wheat germplasm with broadspectrum BYDV resistance

A resistance-like gene identified by EST mapping and its association with a QTL controlling Fusarium head blight infection on wheat chromosome 3BS

Fusarium head blight (FHB) is a major disease in the wheat growing regions of the world. A quantitative trait locus (QTL) on the short arm of chromosome 3B controls much of the variation for resistance. The cloning of candidate disease-resistance genes for FHB QTLs on chromosome 3B can provide further elucidation of the mechanisms that control resistance. However, rearrangements and divergence during plant genome evolution often hampers the identification of sequences with similarity to known disease-resistance genes. This study focuses on the use of wheat expressed sequence tags (ESTs) that map to the region on chromosome 3B containing the QTL for FHB resistance and low-stringency BLAST searching to identify sequences with similarity to known disease-resistance genes. One EST rich with leucine repeats and low similarity to a protein kinase domain of the barley Rpg1 gene was identified. Genetic mapping using a Ning894037 X Alondra recombinant inbred (RI) population showed that this EST mapped to the QTL on the short arm of chromosome 3B and may represent a portion of a newly diverged gene contributing to FHB resistance. The EST is a new marker suitable for marker-assisted selection and provides a starting point to begin map-based cloning for chromosome walking and investigate new diverged genes at this locus. Key words: Fusarium head blight resistance, expressed sequence tags, quantitative trait loci, Rpg1, wheat

Physical location of a HSP70 gene homologue on the centromere of chromosome 1B of wheat (Triticum aestivum L.)

Cereal centromeres consist of a complex organization of repetitive DNA sequences. Several repetitive DNA sequences are common amongst members of the Triticeae family, and others are unique to particular species. The organization of these repetitive elements and the abundance of other types of DNA sequences in cereal centromeres are largely unknown. In this study, we have used wheat-rye translocation lines to physically map 1BL.1RS centromeric breakpoints and molecular probes to obtain further information on the nature of other types of centromeric DNA sequences. Our results, using the rye-specific centromeric sequence, pAWRC.1, indicate that 1BL.1RS contains a small portion of the centromere from 1R of rye. Further studies used molecular markers to identify centromeric segments on wheat group-1 chromosomes. Selected RFLP markers, clustered around the centromere of wheat homoeologous group-1S chromosomes, were chosen as probes during Southern hybridization. One marker, PSR161, identified a small 1BS segment in all 1BL.1RS lines. This segment maps proximal to pAWRC.1 in 1BL.1RS and on the centromere of 1B. Sequence analysis of PSR161 showed high homology to HSP70 genes and Northern hybridization showed that this gene is constitutively expressed in leaf tissue and induced by heat shock and light stimuli. The significance of this work with respect to centromere organization and the possible significance of this HSP70 gene homologue are discussed

Characterization of wheatgrass-derived barley yellow dwarf virus resistance in a wheat alien chromosome substitution line

Wheatgrass (Thinopyrum intermedium) possesses a high level of resistance to barley yellow dwarf virus (BYDV) subgroup I and subgroup II strains. A wheat line (P29), in which the 7D chromosome has been substituted with a group 7 chromosome from T. intermedium, was examined for the level of resistance to two subgroup I and two subgroup II BYDV strains. In P29 plants inoculated with the subgroup I PAV strains, the titer of virus in leaf and stem tissue was typically reduced 42 to 52% when compared with the BYDV-susceptible cv. Abe. P29 and ‘Abe’ had the same content of PAV in roots. These results and the absence of detectable virus in inoculated T. intermedium plants indicate that the complete resistance to subgroup I possessed by the wheatgrass has not been introgressed into P29. In contrast, P29 was completely resistant throughout the plant to the subgroup II strains, NY-RPV and NY-RMV, demonstrating that the complete resistance to subgroup II in T. intermedium was incorporated into P29. Further analysis of this resistance to NY-RPV showed that NY-RPV can replicate in mesophyll protoplasts of P29 and ‘Abe’, suggesting that this resistance is not operating at the single-cell level. Molecular marker analysis confirmed that the T. intermedium chromosome present in P29 is a different group 7 wheatgrass chromosome than that present in L1, a wheat line with BYDV resistance properties similar to those of P29

Structural organization of an alien Thinopyrum intermedium group 7 chromosome in U.S. soft red winter wheat (Triticum aestivum L.)

Barley yellow dwarf virus (BYDV) resistance in soft red winter wheat (SRWW) cultivars has been achieved by substituting a group 7 chromosome from Thinopyrum intermedium for chromosome 7D. To localize BYDV resistance, a detailed molecular genetic analysis was done on the alien group 7 Th. intermedium chromosome to determine its structural organization. Triticeae group 7 RFLP markers and rye specific repetitive sequences used in the analysis showed that the alien chromosome in the P29 substitution line has distinguishing features. The 350–480 bp rye telomeric sequence family was present on the long arm as determined by Southern and fluorescence in situ hybridization. However, further analysis using a rye dispersed repetitive sequence indicated that this alien chromosome does not contain introgressed segments from the rye genome. The alien chromosome is homoeologous to wheat chromosomes 7A and 7D as determined by RFLP analysis. Presence of the waxy gene on chromosomes 7A, 7B, and 7D but its absence on the alien chromosome in P29 suggests some internal structural differences on the short arm between Th. intermedium and wheat group 7 chromosomes. The identification of rye telomeric sequences on the alien Thinopyrum chromosome and the homoeology to wheat chromosomes 7A and 7D provide the necessary information and tools to analyze smaller segments of the Thinopyrum chromosome and to localize BYDV resistance in SRWW cultivars.Key words: barley yellow dwarf virus, Thinopyrum intermedium, rye repetitive sequences, RFLP, homoeologous group 7

AFLP and AFLPderived SCAR markers associated with Striga gesnerioides resistance in cowpea

Cowpea, Vigna unguiculata (L.) Walp., is an important grain legume grown in tropical and subtropical regions, primarily Africa. The parasitic weed Striga gesnerioides (Willd.) Vatke is one of the most important constraints to cowpea production. Host plant resistance is the only practical control method. Five virulence genotypes (races) of S. gesnerioides have been identified in different regions of Africa. Several host resistance genes have also been identified that are effective against specific races of S. gesnerioides The rapid spread of this parasitic weed creates an urgent need for cowpea varieties with multiple resistance genes. A recently identified cowpea breeding line, IT93K-693-2, has resistance to all known races. The objective of this research was to develop DNA markers that are useful for marker-assisted selection (MAS) in breeding cowpea for resistance to S. gesnerioides An F2 population developed from the cross between IT93K-693-2 and the susceptible cultivar IAR1696 was characterized for resistance against race 3 of S. gesnerioides for genetic analysis and molecular mapping. IT93K-693-2 was found to have a single dominant gene for resistance. Four amplified fragment length polymorphism (AFLP) markers, designated E-ACT/M-CTC115, E-ACT/M-CAC115, E-ACA/M-CAG108 and E-AAG/E-CTA190, were identified and mapped 3.2, 4.8, 13.5 and 23.0 cM, respectively, from Rsg1, a gene in IT93K-693-2 that gives resistance to race 3 (or Nigerian strain) of S. gesnerioides The first two markers were validated in a second F2 population developed from crossing the same resistant parent with ‘Kamboinse local’, a different susceptible cultivar. The AFLP fragment from marker combination E-ACT/M-CAC, which is linked in coupling with Rsg1 was cloned, sequenced, and converted into a sequence characterized amplified region (SCAR) marker named SEACTMCAC83/85, which is codominant and useful in breeding programs