Purification of pea enation mosaic virus from its pea aphid vector, Acyrthosiphon pisum, and aphid-transmission characteristics

Abstract

Pea enation mosaic virus (PEMV) was purified from pea aphids by a system involving chloroform-butanol emulsification, differential centrifugation, and density gradient centrifugation. The product was highly infectious when transmitted to pea plants by pea aphids, and it was extracted in sufficiently high concentration to be monitored in centrifuged sucrose columns with a UV scanner. Electron micrographs showed that purified preparations contained an abundance of virus particles that measured ca. 27 nm in diameter and were indistinguishable from those isolated from infected plants. No virus particles were detected in preparations of nonviruliferous aphids, and no infectivity was obtained from these preparations in either aphid or mechanical transmission tests. Virus purified from an aphid source was established in pea plants by mechanical transmission and compared as to aphid-transmissibility with a virus line from a plant source; both lines were initiated with the same PEMV strain. The aphid-source virus line was transmitted by pea aphid first-stage nymphs with significantly ( P < 0.05) higher efficiency than the plant-source virus line after 1- and 4-hr acquisition-access periods, and it was transmitted with characteristics superior to those previously recorded for PEMV-pea aphid relationships. First-instar pea aphids were 95.8% efficient in transmission of the aphid-source virus after only a 4-hr acquisition-access period on infected pea plants. The virus line when acquired from infected plants had a median latent period (LP 50) in the first instar of only 5.7 hr.