Propagation of black raspberry necrosis virus (BRNV) in mixed culture with solanum nodiflorum mottle virus, and the production and use of BRNV antiserum

Abstract

SUMMARYThe concentration of particles of black raspberry necrosis virus (BRNV), which is normally extremely low in herbaceous plants, increased about 1000‐fold when Nicotiana clevelandii plants were inoculated with a mixture of BRNV and an unrelated virus, solanum nodiflorum mottle (SNMV). In sap from N. clevelandii infected with the mixed culture, BRNV infectivity survived dilution to 10˜4 but not 10˜5, and storage for 6 but not 8 days at 20 oC, for 6 but usually not 10 days at 4 oC and for more than 13 days at – 15 oC. When plants were inoculated with the mixed culture, BRNV induced typical symptoms in several Chenopodium species and infected several previously unreported hosts. Purified preparations of particles of the mixed culture contained only a small proportion of BRNV particles, which sedimented in sucrose density gradients as two components, one, probably non‐infective, of c. 505, and the other, infective, of 120‐130S. An antiserum prepared to purified particles of the mixed culture was cross‐absorbed with SNMV particles and used in indirect ELISA to detect BRNV in herbaceous plants infected with the mixed culture, and also in a wide range of Rubus species, cultivars and hybrids infected naturally, by grafting or by inoculation with the aphid Amphorophora idaei. The reliability of ELISA for detecting BRNV in raspberry leaves depended on the cultivar and time of year. Some cultivars, such as Glen Clova, had low concentrations of BRNV, which was detected reliably only in late spring/early summer, whereas other cultivars, such as Lloyd George and Mailing Enterprise, had greater BRNV concentrations.In small‐scale surveys in eastern Scotland, BRNV was detected by ELISA in many raspberry cvs, including some that contain major gene resistance to the vector, A. idaei; in five of nine raspberry stocks entered for the Standard grade certificate but in none of five stocks entered for the Stock Cane certificate; and in 40% of wild raspberry and 14% of wild bramble plants growing near commercial raspberry crops. The significance of these findings for the control of BRNV is discussed.