Fifteen strains of Agrobacterium were investigated for their ability to agroinfect wheat dwarf virus into 4-day-old wheat seedlings. Viral infection was determined by ELISA. The greatest proportionof plants infected by any strain was 55%, achieved by the Agrobacterium rhizogenes strain Ar2629. In general, A. rhizogenes strains were found to give a higher proportion of agroinfected plants than A. tumefaciens strains. Nopaline types of A. tumefaciens were superior to octopine types in their ability to transfer DNA to wheat plants, but some strains ofthe latter type did infect to a low frequency. Seedling size at inoculation had no effect on the number of plants that developed a viral infection, although seedlings with shoots less than 1.0 cm long were not likely to survive damage caused by the inoculation procedure. The experiment was replicated over time and no significant variation was found between the three sets of data obtained.

Parameters affecting the efficiency of agroinfection of maize streak virus (MSV) in maize have been determined. Monomeric units, cloned at a number of sites in the MSV genome were not infectious but multimeric units containing partial duplications were equally as infectious as complete tandem dimeric clones. Inoculation of tandem dimeric units conjugated into different strains of Agrobacterium showed that both A. tumefaciens and A. rhizogenes were able to transfer DNA to maize and this ability was Ti (or Ri) plasmid-specific. Nopaline strains of A. tumefaciens and both agropine and mannopine A. rhizogenes strains efficiently transferred MSV DNA to maize. A number of strains were capable of MSV DNA transfer to other members of the Gramineae, providing information which may be essential for Agrobacterium-mediated transformation of monocotyledonous plants.

Abstract Various inoculation procedures of in vitro grown wheat seedlings with Agrobacterium tumefaciens carrying a wheat dwarf virus (WDV) dimer led to 13–46% agroinfection. Deliberate wounding of seedlings during or before inoculation gave higher agroinfection rates than in seedlings without wounding. Seedlings from 1–4 days old were equally receptive to inoculations in the meristematic regions. Vacuum infiltration of the Agrobacterium inoculum into excised cultured wheat embryos gave up to 35% agroinfection (with 4 ωg 1−1 acetosyringone). WDV was detectable in seedlings by the ELISA assay 4 days after inoculation and there was good agreement between the ELISA and DNA dot blot assays of virus infection. Agrobacterium was found to deliver DNA (WDV) to the three wheat varieties tested and to Aegilops speltoides, Triticum monococcum and T. durum.

A polypeptide of approximately 11 000 daltons (11 kDa protein) encoded by an open reading frame (10.9 ORF) from the virion sense of maize streak virus (MSV) DNA has been detected among the products of in vitro translation reactions programmed with RNA from infected maize plants and also in total protein extracts from infected leaves. The 11 kDa protein has not been detected in virions and is therefore proposed to have a nonstructural role.