TRANSMISSION OF VIRUSES BY PLANT NEMATODES

Longidorid and trichodorid nematodes transmit nepo- and tobraviruses, respectively. A specific association exists between vectors and their viruses which is a consequence of the nature, site and mechanism of vi rus particle retention within the vector, It is correlated with the se rological properties of the virus coat protein and determined by the R NA-2 segment of the virus genome and by an inherited character of the vector. The virus coat protein is probably involved in the recognition process between vector and virus but is not the sole determinant for transmission of tobraviruses. Genetic changes made to proteins present in the RNA-2 segment of pea early-browning tobravirus have been used to reveal the probable involvement of several proteins in vector trans mission. ''Protruding'' C-terminal amino acid sequences of tobaviruses possibly link, with the aid of a viral determined helper factor, to t he site of retention.