THRIPS-FACILITATED TRANSMISSION OF PRUNE DWARF AND PRUNUS NECROTIC RINGSPOT VIRUSES FROM CHERRY POLLEN TO CUCUMBER

When pollen from sweet and sour cherry trees infected by Prunus necrotic ringspot virus (PNRSV) and prune dwarf virus (PDV) was dusted onto cucumber seedlings and the seedlings were caged with eight to 15 Frankliniella occidentalis for 1 day, approximately 20% (68 of 332) of the seedlings subjected to the thrips plus infective pollen treatment became infected. Only one of 188 cucumber seedlings caged with cherry pollen only became infected. No infection occurred when thrips were caged without pollen. The rate of transmission varied greatly with the virus isolates used. The five pollen inoculum sources that gave highest transmission (25-75%) were from trees having dual (PDV + PNRSV) infections. Four of the six pollen inoculum sources giving less than 10% infection were from trees infected with either PDV or PNRSV alone. The overall transmission of PDV was four times greater than that of PNRSV. In tests with virus-contaminated sweet cherry pollen that had been stored frozen for 2 yr, PDV but not PNRSV was transmitted by F. occidentalis to nine of 24 (37%) cucumber seedlings.