Strains of Soybean Mosaic Virus: Aphid Transmission, Host Passage Effects, and Use in Evaluation of Genetic Resistance in Soybeans

120 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.Seven soybean mosaic virus (SMV) strains proved to be aphid transmissible, however, one isolate of strain G5 lost its aphid transmissibility after about 30 successive passages by sap inoculation through a susceptible soybean cultivar Rampage during 20 months. The aphid nontransmissible strain G5 (designated NG5) was used to study the mechanism of aphid nontransmissibility.NG5 was not transmitted from sequential acquisition access experiments when SMV strains G3 or G4 or potato virus Y (PVY) was used as a possible helper source. NG5 was transmitted, however, from plants doubly infected with SMV strain G3 or G4 and NG5.Five aphid species Aphis citricola, A. craccivora, Myzus persicae, Rhopalosiphum maidis, and R. padi were able to transmit a single isolate representing each of the seven SMV strains except that the isolate of strain G3 was not transmitted or was very inefficiently transmitted by R. maidis and R. padi. Field spread of four selected SMV strains G2, G3, G6 and G7 was studied, and the spread of the G6 was significantly greater than that of the others.Forty six soybean entries reported to be resistant to SMV were evaluated for reactions to seven SMV strains. Among them, six soybean lines were found to be resistant to all seven SMV strains used. Reaction types for the other entries were similar to one of the five soybean differentials (Suweon 97, Buffalo, Kwanggyo, Davis, and Ogden).Variability in virulence of SMV strains has been observed in greenhouse studies during maintenance of the virus by sap inoculations. My results show that pathogenic variants of SMV strains can be obtained by host passage effects.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD