Z6／陕7859胚培养再生植株的细胞遗传学研究与易位系选育

二体附加系Ｚ６携带抗大麦黄矮病毒病基因,为了将其抗性导入小麦,将Ｚ６与普通小麦陕７８５９杂交,杂种Ｆ１经幼胚培养诱导形成再生植株,对再生植株及后代进行抗性鉴定,农艺性状考察及对ＳＣ２部分抗病植株花粉母细胞减数分裂期染色体行为进行了观察。结果表明,（１）ＳＣ２不同单株间存在染色体数目,结构的变异。（２）同一再生植株后代的不同单株,染色体数目可能相同,但染色体组成及减数分裂期行为可心不同,致使后代抗性     

The occurrence of barley yellow dwarf viruses in CIMMYT bread wheat nurseries and associated cereal crops during 1988–1990

Enzyme-linked immunosorbent assay (ELISA)-based surveys of the occurrence of five barley yellow dwarf virus (BYDV) serotypes (MAV, PAV and SGV in “Group 1”; RPV and RMV in “Group 2”) in CIMMYT bread wheat nurseries and other small grain crops in various locations world-wide were undertaken in 1988, 1989 and 1990. The objective was to investigate the relative occurrence of BYDV serotypes in areas relevant to CIMMYT cereal breeding programs. Overall, MAV and PAV serotypes predominated in the samples collected, though their relative frequencies depended on the location. SGV serotypes were uncommon in most locations. Group 2 serotypes occurred widely, but RMV serotypes were more common than RPV serotypes.     

Research progress in BYDV resistance genes derived from wheat and its wild relatives

Barley yellow dwarf virus （BYDV） may cause a serious disease affecting wheat worldwide. True resistance to BYDV is not naturally found in wheat. BYDV resistance genes are found in more than 10 wild relative species belonging to the genera of Thinopyrum, Agropyron, Elymus, Leymus, Roegneria, and Psathyrostachy. Through wide crosses combining with cell culture, use ofph mutants, or irradiation, 3 BYDV resistance genes in Th. intermedium, including Bdv2, Bdv3 and Bdv4, were introgressed into common wheat background. Various wheat-Th, intermedium addition and substitution, translocation lines with BYDV-resistance were developed and characterized, such as 7D-TAi#1 （bearing Bdv2）, 7B-7Ai#1, 7D-7E （beating Bdv3）, and 2D-2Ai-2 （bearing Bdv4） translocations. Three wheat varieties with BYDV resistance from Th. intermedium were developed and released in Australia and China, respectively. In addition, wheat-Agropyron cristatum translocation lines, wheat-Ag, pulcherrimum addition and substitution lines, and a wheat-Leymus multicaulis addition line （line24） with different resistance genes were developed. Cytological analysis, morphological markers, biochemical markers, and molecular markers associated with the alien chromatin carrying BYDV resistance genes were identified and applied to determine the presence of alien, chromosomes or segments, size of alien chromosome segments, and compositions of the alien chromosomes. Furthermore, some resistance-related genes, such as RGA, P450, HSP70, protein kinases, centrin, and transducin, were identified, which expressed specifically in the resistance translocation lines with Bdv2. These studies lay the foundations for developing resistant wheat cultivars and unraveling the resistance mechanism against BYDV.     

Suitability of the biomass crop Miscanthus sinensis as a host for the aphids Rhopalosiphum padi (L.) and Rhopalosiphum maidis (F.), and its susceptibility to the plant luteovirus Barley Yellow Dwarf Virus

1 The reproductive performance of two aphid pest species, Rhopalosiphum padi and Rhopalosiphum maidis, was investigated on two seedling growth stages of Miscanthus sinensis, rhizomatous M. sinensis‘Giganteus’ and barley. Rhopalosiphum padi was unable to complete its development on Miscanthus. Rhopalosiphum maidis was most fecund on rhizomatous plants compared with seedling stages. 2 The ability of R. maidis to transmit the RPV isolate of Barley Yellow Dwarf Virus (BYDV) to M. sinensis seedlings was further investigated. Following successful transmission, host plant symptomology and the effect of infection on the yield of Miscanthus were investigated. Total above soil biomass was reduced by around 23% following infection. 3 The inability of R. padi to utilize Miscanthus is reviewed in light of this species’ origin and inability to utilize C₄ host plants. 4 The potential pest status of R. maidis on Miscanthus is discussed together with the impact that Miscanthus cultivation could have on the ecology of this aphid species and BYDV in the U.K.     

Occurrence of barley yellow dwarf virus (BYDV) isolates in different farmland habitats in western France and south-west England

The incidence and distribution of the three principal isolates of barley yellow dwarf virus (PAV, RPV and MAV) are described in winter cereal crops, cereal (stubble) regrowth and grasses from 11 sites in western France and south-west England during 1987 and 1988. Isolates were identified by indirect ‘sandwich’ ELISA using the monoclonal antibodies MAC91, MAC92 and MAFF2. More virus infection occurred in all localities and in most of the plant communities sampled, with the exception of perennial grass leys, in 1987 than in 1988. All three isolates were widespread. MAV was associated more with sites further north and PAV more with those further south. The geographical distribution of RPV was less variable. Underlying these trends, the relative abundance of isolates differed considerably between habitats. RPV always predominated in perennial grass leys and MAV in most cereal crops, although in the latter MAV was less prevalent in 1987 than in 1988. The greatest regional difference was found in stubble regrowth where PAV predominated in France but MAV predominated in England. Grasses from field margins (only sampled in England) were mainly infected by MAV and RPV. The implications of these findings for the epidemiology of BYDV are discussed, especially the roles of different host plant communities or habitats in the annual infection cycle of small-grain cereals.     

Aerial flow of barley yellow dwarf viruses and of their vectors in western France

During the years 1989–1992 cereal aphids were caught alive in a low level (1.5 m high) suction trap operated in Le Rheu (Brittany, France) and tested for BYDV transmission. In most cases comparisons with data collected simultaneously by a 12.2 m suction trap operating in the same site resulted in good relationships between weekly catches at both heights. Results from transmission tests showed that: (i) the two main BYDV vectors were Rhopalosiphum padi and Metopolophium dirhodum during the years of experiment; (ii) PAV and MAV were the commonest viruses and RPV was relatively scarce; (iii) during spring M. dirhodum appeared to be the most important MAV vector and nearly as good a PAV vector as R. padi; (iv) during autumn R. padi was the only vector of the three viruses with mixed transmission allowing it to transmit also MAV probably by heteroencapsidation. To give an indication of the risk of infection, infectivity indices were calculated by multiplying the numbers of aphids caught by the 12.2 m suction trap by the proportion that were infective. These infectivity indices agreed with field records of primary infections.     

Vector specificity of barley yellow dwarf virus serotypes and variants in southwestern Idaho

Plants with symptoms of barley yellow dwarf virus (BYDV) obtained in infection feeding assays of aphids collected in the field in Idaho between 1986 and 1988 were tested for virus transmissibility by possible aphid vectors. Isolates obtained during 1987–1988 were also tested with a range of polyclonal antisera which distinguished PAV, MAV, SGV, RPV and RMV serotypes. In 1989 some Idaho (ID) BYDV isolates, maintained as standards for comparison, were serotyped and tested for aphid transmissibility, using 11 species of aphids. There was not always the expected correspondence between serotype and vector specificity for ID isolates. For isolates obtained from field-collected Rhopalosiphum padi, vector transmissibility and serotype corresponded with previous reports; however, 44% of isolates which were serotyped as RMV were also transmissible by species other than Rhopalosiphum maidis. Similarly, the transmissibility of the ID laboratory standards did not always conform to the reported vector specificity of serotypes. The laboratory ID-MAV culture was transmitted by Metopolophium dirhodum and Myzus persicae as well as by Sitobion avenae. The laboratory ID-SGV culture was transmitted by R. padi and 5. avenae as well as by Schizaphis graminum. The ID-RPV culture was transmitted by S. graminum and Rhopalosiphum insertum as well as R. padi. Both of two laboratory ID-RMV cultures were transmissible by R. insertum and R. padi transmitted one of them. The results indicate that, for isolates collected in Idaho, vector specificity cannot be assumed from their serotypes.     

Temporal dynamics of spread of four viruses within mixed species perennial pastures

Six mixed species, perennial pastures at two locations, A (four pastures) and B (two pastures), were sampled at regular intervals over periods of 10 to 22 months. The predominant plant species present were white clover (Trifolium repens), perennial ryegrass (Lolium perenne) and kikuyu grass (Pennisetum clandestinum). To determine the extent to which incidences of viruses transmitted in different ways change in the same pastures over time, samples of each plant species were taken at random on every visit and tested for virus presence. To help identify factors that might explain changes in virus incidence, records were also made of aphid presence, pasture management practices, grazing regimes, sward height and the relative proportions of different plant species within the swards. Samples of white clover were tested for presence of Alfalfa mosaic virus (AMV) and White clover mosaic virus (WCMV), ryegrass for Barley yellow dwarf virus (BYDV) and Ryegrass mosaic virus (RyMV), and kikuyu grass for BYDV and potyvirus infection. AMV and WCMV were detected in white clover, and BYDV and RyMV in ryegrass at both locations but often with wide incidence fluctuations for the individual viruses. AMV incidences in white clover ranged from 0% to 19% at A, and from 27% to 100% at B. WCMV incidences in white clover fluctuated between 9% and 46% at B, but never exceeded 1% at A. RyMV incidences in ryegrass fluctuated between 3% and 34% at A, and 19% and 73% at B. BYDV incidences in ryegrass ranged from 0% to 6% at A and 4% to 17% at B. In kikuyu grass, an unknown potyvirus and BYDV were detected twice (1% incidence) and once (4% incidence) respectively at B, and the unknown potyvirus only once (2% infection) at A. During repeated trapping of aphids in four pastures (two each at A and B), numbers of aphids caught varied widely between trapping dates and between individual pastures on the same trapping date. The species caught were Acyrthosiphon kondoi, A. pisum, Aphis craccivora, Rhopalosiphum padi and Therioaphis trifolii. Except in summer, when only T. trifolii was caught, A. craccivora was the most abundant. The trends in incidence for each virus within each pasture were compared with those from the other pastures sampled over identical periods to determine whether there was any commonality. For RyMV in ryegrass, overall incidence trends within the different pastures at both locations resembled each other during the same sampling periods. Within pastures at the same location there was commonality in incidence trends for RyMV and BYDV in ryegrass, but with AMV in white clover periods of similarity were rare even when pastures were adjacent and managed identically. Unravelling the individual effects of alterations in season, vector numbers, mowing, intermittent heavy grazing and pasture species composition on virus incidence proved difficult due to complex interactions between these and other factors influencing new spread or declining virus occurrence.