VIRAL DETERMINANTS OF PEA EARLY BROWNING VIRUS SEED TRANSMISSION IN PEA

Pea early browning virus (PEBV) is a member of the genus, Tobravirus. It is transmitted by soil-inhabiting trichodorid nematodes and through seeds from diseased plants. By introducing mutations into the PEBV ge nome, we have studied the viral determinants of seed transmission in p ea. Neither deleting a portion of the genome containing the three nons tructural genes in RNA2 nor the interuption of any of the three genes individually prevented PEBV seed transmission. However, a comparison o f two PEBV isolates indicated a minor role for RNA2 or its products. I n contrast, the removal of the coding sequence of the 12K gene in RNA1 almost completely abolished viral seed transmission. The virus lackin g the 12K gene caused more severe symptoms on leaves and pods, and acc umulated to a higher level than the wild-type virus in both types of t issues. However, the 12K deletion mutant accumulated poorly in anthers and carpels, and could not be detected in pollen grains and ovules. T hese results suggest that the 12K gene is involved in the infection of the gametic cells and hence the seed transmission of PEBV in pea. (C) 1997 Academic Press.