Wild relatives of common wheat, Triticum aestivum, and related species are an important source of disease and pest resistance and several useful traits have been transferred from these species to wheat. C-banding and in situ hybridization analyses are powerful cytological techniques allowing the detection of alien chromatin in wheat. C-banding permits identification of the wheat and alien chromosomes involved in wheat-alien translocations, whereas genomic in situ hybridization analysis allows determination of their size and breakpoint positions. The present review summarizes the available data on wheat-alien transfers conferring resistance to diseases and pests. Ten of the 57 spontaneous and induced wheat-alien translocations were identified as whole arm translocations with the breakpoints within the centromeric regions. The majority of transfers (45) were identified as terminal translocations with distal alien segments translocated to wheat chromosome arms. Only two intercalary wheat-alien transloctions were identified, one induced by radiation treatment with a small segment of rye chromosome 6RL (H25) inserted into the long arm of wheat chromosome 4A, and the other probably induced by homoeologous recombination with a segment derived from the long arm of a group 7 Agropyron elongatum chromosome with Lr19 inserted into the long arm of 7D. The presented information should be useful for further directed chromosome engineering aimed at producing superior germplasm.

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

Tissue culture generates a wide range of genetic variation in plant species which can be incorporated in plant breeding programmes By in vitro selection, mutants with useful agronomic traits, eg salt or drought tolerance or disease resistance, can be isolated in a short duration The successful use of somaclonal variation is very much dependent on its genetic stability in the subsequent generations for which molecular markers such as RAPDs, AFLPs, SSRs and others can be helpful The potential of somaclonal variation has yet to be fully exploited by breeders, even though a few cultivars have been developed in crops such as Brassica juncea, rice and others

Tissue culture-derived variation in crop improvement

Barley yellow dwarf viruses represent one of the most economically important and ubiquitous groups of plant viruses. This review focuses primarily on four research areas in which progress has been most rapid. These include (a) evidence supporting reclassification of BYDVs into two genera; (b) elucidation of gene function and novel mechanisms controlling gene expression; (c) initial forays into understanding the complex interactions between BYDV virions and their aphid vectors; and (d ) replication of a BYDV satellite RNA. Economic losses, symptomatology, and means of control of BYD are also discussed.

Barley yellow dwarf viruses.

Wheat (Triticum spp. L.) breeders have significantly improved wheat adaptation to stress-prone environments around the world. This progress has largely been achieved using empirical selection and genetic variability within the primary wheat gene pool. As most stress tolerance traits are quantitatively inherited, expansion of the available genetic diversity for stress tolerance is necessary if rates of genetic progress are to be maintained. This review explores three sources of novel genetic variability, namely synthetic wheat, landrace cultivars, and alien introgressions and their applicability to applied wheat breeding. Synthetic hexaploid wheat, derived by crossing tetraploid wheat with Aegilops tauschii, provides new genetic variability for adaptation to drought, high temperature, salinity, waterlogging, and soil micronutrient imbalances from the secondary wheat gene pool. Synthetic-derived materials have performed well in many stressed environments globally. There is significant unexploited variation among landraces and modern wheat cultivars to improve the stress adaptation of cultivated wheat. The tertiary gene pool, with a few significant exceptions, has been more difficult to exploit due to complex inheritance, meiotic instability, and linked deleterious effects. Nevertheless, there is sufficient genetic variation in the wheat gene pool to ensure the continued improvement of wheat adaptation to abiotic stress.

Novel Germplasm Resources for Improving Environmental Stress Tolerance of Hexaploid Wheat

Barley yellow dwarf virus-PAV (BYDV-PAV) is the most serious and widespread virus of cereals worldwide Natural resistance genes against this luteovirus give inadequate control, and previous attempts to introduce synthetic resistance into cereals have produced variable results In an attempt to generate barley with protection against BYDV-PAV, plants were transformed with a transgene designed to produce hairpin (hp)RNA containing BYDV-PAV sequences From 25 independent barley lines transformed with the BYDV-PAV hpRNA construct, nine lines showed extreme resistance to the virus and the majority of these contained a single transgene In the progeny of two independent transgenic lines, inheritance of a single transgene consistently correlated with protection against BYDV-PAV This protection was rated as immunity because the virus could not be detected in the challenged plants by ELISA nor recovered by aphid feeding experiments In the field, BYDV-PAV is sometimes associated with the related luteovirus Cereal yellow dwarf virus-RPV (CYDV-RPV) When the transgenic plants were challenged with BYDV-PAV and CYDV-RPV together, the plants were susceptible to CYDV-RPV but immune to BYDV-PAV This shows that the immunity is virus-specific and not broken down by the presence of CYDV It suggests that CYDV-RPV does not encode a silencing-suppressor gene or that its product does not protect BYDV-PAV against the plant's RNAi-like defence mechanism Either way, our results indicate that the BYDV-PAV immunity will be robust in the field and is potentially useful in minimizing losses in cereal production worldwide

A single copy of a virus-derived transgene encoding hairpin RNA gives immunity to barley yellow dwarf virus.

Barley yellow dwarf virus (BYDV) resistance has been transferred to wheat from a group 7 chromosome of Thinopyrum (Agropyron) intermedium. The source of the resistance gene was the L1 disomic addit...

The use of cell culture for subchromosomal introgressions of barley yellow dwarf virus resistance from Thinopyrum intermedium to wheat

Resistance to barley yellow dwarf virus (BYDV) has been described in lines derived from crosses between wheat and Thinopyrum intermedium. The resistance in one such line, Zhong 4, originating in China, was expressed against two different serotypes of BYDV as measured by accumulation of virus in infected seedlings. F1 hybrids between wheat (2n = 42) and Zhong 4 (2n = 56) had 49 chromosomes and intermediate levels of virus when compared to the parent lines. Cytological and molecular hybridization studies suggested that the BYDV resistance in Zhong 4 is carried on a set of seven pairs of nonwheat chromosomes that derived from a combination of the E and X genomes present in Th. intermedium.Key words: Barley yellow dwarf virus, wheat, ribosomal DNA, Agropyron intermedium, Thinopyrum intermedium, virus resistance.

Characterization of a potential source of barley yellow dwarf virus resistance for wheat

Barley yellow dwarf virus (BYDV) is one of the most serious wheat diseases in China So far no resistance has been described in common wheat A certain level of BYDV resistance was found in thirteen Triticeae species Thinopyrum intermedium, two octoploids derived from TH intermedium/wheat, Zhong 4 awnless and TAF46, and one disomic addition line, L1 derived from TAF46, showed good resistance to BYDV by enzyme linked immunosorbent assay (ELISA) Two wheat/TA intermedium translocation lines, CPI 119880 and CPI 119899, showing good BYDV resistance were developed from L1 by using both CSph mutant and tissue culture It is found that their BYDV resistance was controlled by a single dominant gene Two cDNA probes pEleAcc3 and pPJN8 (E1-T1) were screened for detecting Th intermedium DNA in wheat background A specific band for the DNA of Th intermedium and its derivatives was found in Southern hybridization It is also possible to determine the size of the alien segment by comparing the relative density of the specific band Therefore, this can be used as a marker to identify the BYDV resistance in wheat breeding program

Development of common wheat germplasm resistant to barley yellow dwarf virus by biotechnology.

GPV is a Chinese serotype isolate of barley yellow dwarf virus (BYDV) that has no reaction with antiserum of MAV, PAV, SGV, RPV and RMV The sequence of the coat protein (CP) of GPV isolate of BYDV was identified and its amino acid sequence was deduced. The coding region for the putative GPV CP is 603 bases nucleotides and encodes a Mr 22 218 (22 ku) protein. The same as MAV, PAV and RPV, GPV contained a second ORF within the coat protein coding region. This protein of 17 024 Mr (17 ku) is thought to correspond to the Virion protein genome linked (Vpg). Sequence comparisons of the CP coding region between the GPV isolate of BYDV and other isolates of BYDV have been done. The nucleotide and amino acid sequence homology of GPV has a greater identity to the sequence of RPV than those of PAV and MAV. The GPV CP sequence stored 83.7% of nucleotide similarity and 77.5% of deduced amino acid similarity, whereas that of the PAV and MAV shared 56.9%, 53.2% and 44.1%, 43.8% respectively. According to BYDV-GPV CP sequence, two primers were designed. The cDNA of CP was produced by RT-PCR. Full-length cDNA of CP was inserted into plasmid to construct expression plasmids named pPPI1, pPPI2 and pPPI5 based on different promoters. The recombinant plasmids were identified by using α-32P-dATP labelled CP probe, α-32P-ATP labelled GPV RNA probe and sequencing to confirm real GPV CP gene cDNA in plasmids.

G. H. Zhou

Papers

The use of cell culture for subchromosomal introgressions of barley yellow dwarf virus resistance from Thinopyrum intermedium to wheat

The use of cell culture for subchromosomal introgressions of barley yellow dwarf virus resistance from Thinopyrum intermedium to wheat

Characterization of a potential source of barley yellow dwarf virus resistance for wheat

Development of common wheat germplasm resistant to barley yellow dwarf virus by biotechnology.

Nucleotide sequence of coat protein gene for GPV isolate of barley yellow dwarf virus and construction of expression plasmid for plant