Seedlot samples of 570 Plant Introduction (PI) accessions of L. culinaris were planted in greenhouses and the resultant seedlings were tested for the presence of seed-borne virus by local lesion assays on Chenopodium amaranticolor leaves. A seed-borne virus, designated the lentil strain of pea seed-borne mosaic virus (PSbMV-L), was detected in 38 of 570 accessions. Incidence of PSbMV-L in 5 selected accessions ranged from < 5 to 10%. Although plants of PI accessions arising from infected seeds usually showed no symptoms, isolates from infected accessions readily induced severe symptoms in plants of commercial lentil cultivars including Chilian, Tekoa and Precoz. Of 23 other plant species and cultivars tested as possible hosts, PSbMV-L was infectious only to C. amaranticolor, Vicia faba var. minor, and 1 Tempter of 25 pea cultivars. The virus was not seed transmitted in ''Tempter'' peas. PSbMV-L was transmitted from infected to healthy ''Tekoa'' lentil plants by sets of 3 pea aphids (Acyrthosiphon pisum) at frequencies ranging 55-88%. PSbMV-L was distinguished from the standard USA strain of PSbMV by nonpathogenicity to most pea cultivars, by pathogenicity to L. culinaris germ plasm sources independently of PSbMV-immunity-conferring gene sbv, by an inoculum reservoir apparently restricted to infected lentil seed, by comparative enzyme-linked immunosorbent assay and by intrinsic particle instability. Conversely, the 2 strains produced identical symptoms in ''Tekoa'' lentil and on leaves of C. amaranticolor, and were indistinguishable by SDS[sodium dodecyl sulfate]-gel immunodiffusion serology or by immunosorbent electron microscopy.