SUMMARYIn glasshouse experiments, barley seedlings were inoculated with barley yellow mosaic virus (BaYMV) either mechanically or by using zoospores or cystosori of a viruliferous isolate of the vector, Polymyxa graminis, maintained on barley in sand culture.Experiments using mechanical inoculation showed that seedlings became more resistant with age. Consistent cultivar differences were obtained: cvs Maris Otter and Halcyon were very susceptible and cv. Athene seemed immune. Symptoms developed more rapidly at 23 than at 17 or 11 oC. After vector inoculation, symptoms developed more slowly than after mechanical inoculation but cultivar ranking was similar. Cultivars did not differ in susceptibility to the vector, as measured by zoospore production on their roots. Spring barley cultivars supported the growth of the vector which remained viruliferous and some showed symptoms although, in the field, symptoms do not appear on spring‐sown crops.

S U M M A R YResting spores (cystosori) of Polymyxa graminis, selected from roots of barley plants infected with barley yellow mosaic virus (BaYMV), were used to start monofungal sand cultures. Out of 20 attempts using over 800 cystosori, P. graminis became established in 12, and in two of these BaYMV symptoms also occurred.BaYMV was detected by ELISA in extracts of dried roots heavily infected with cystosori and in zoospores of P. graminis. Calculations suggested that, on average, each zoospore carried less than 100 virus particles. 0 1988 Association of Applied Biologists

A viruliferous isolate of the fungal vector Polymyxa graminis was grown on roots of barley cultivars immune or susceptible to barley yellow mosaic virus (Bay MV). Zoospores or resting spores of the vector produced on different cultivars were then inoculated to a virus-susceptible test cultivar. Although the vector established in all treatments, transmission of BaYMV was rare and usually nil from immune cultivars; amounts of virus detected serologically in their roots were very low, thus showing that resistance was to virus multiplication. If immune cultivars decrease the virus content of vector populations in the field, this would have important implications for disease control.

S U M M A R YCultures of Polymyxa graminis were maintained in roots of barley plants grown in sand at different temperatures using Wisconsin soil temperature tanks. At 17 -20"C, the minimum time from inoculation with cystosori to the production of zoospores from the inoculated roots was 2 -3 wk. At 1 1 -20°C many zoospores were produced but the incubation period was longer at the lower temperatures. Above 20°C little fungal development occurred.The duration of motility of zoospores ranged from c. 1 h to > 24 h. Bovine serum albumen (BSA) prolonged motility but glycine and glucose had no effect or, at higher concentrations, were toxic. Zoospores were rapidly immobilised by zinc ions in solution at or above 10 pg/ml.In some experiments BSA added to the zoospore suspension greatly increased transmission of barley yellow mosaic virus (Bay MV) while glucose, glycine and ovalbumen decreased it. When seedlings were incubated with zoospore suspensions for 24 h at different temperatures, BaYMV transmission was high (> 60%) at 10, 15 and 20°C but there was little at 5 or 25°C. In experiments to determine. the time taken for zoospore penetration, seedlings were incubated in suspension for different periods of time and then rinsed in zinc sulphate solution to kill free zoospores. Between 3 and 3.5 h was needed for zoospores to establish infection. Transmission occurred equally to plants of various ages between 3 days and 7.5 wk.0 1988 Association of Applied Biologists

S U M M A R YOat golden stripe virus (OGSV) was maintained in oats by mechanical inoculation and purified by extraction of leaves in borate buffer, two cycles of centrifugation through sucrose cushions and isopycnic centrifugation in CsCI. An antiserum with a titre of 1/1024 in precipitin tests was prepared. Particle length distribution was bimodal with median values, respectively, of 150 and 300 nm from dip preparations. Measurements from immunosorbent electron microscopy (ISEM) and purified preparations showed that the particles had partially degraded during these procedures. The virus sedimented as two components of 168 S and 218 S and had a buoyant density of 1.321 g ~m -~.Four isolates of OGSV reacted with the antiserum. Antiserum to members and possible members of the furovirus group were tested in ISEM decoration tests and in ELISA. OGSV was related to soil-borne wheat mosaic virus but not to beet necrotic yellow vein virus, hypochoeris mosaic virus or potato mop-top virus.