Influence of in vitro factors on titre and elimination of model fruit tree viruses

The titre of apple chlorotic leaf spot virus (ACLSV) was higher in microplants of Malus domestica cv. Jonagold than in 2-year-old grafted scions. Cytokinin concentration in the medium increased the titre of prunus necrotic ringspot virus (PNRSV) in the apex of microplants of Prunus insititia cv. Kozlienka but did not affect the titre of ACLSV in M. domestica. Virus titre of ACLSV was higher in the haulms of autotrophically-grown compared with heterotrophically-grown microplants whereas as for PNRSV the results were the reverse. For both viruses, however, titre of the virus in the roots of autotrophically-grown plants was significantly higher than in haulm tissue from heterotrophic cultures. Ribavirin incorporation resulted in elimination of both viruses. Negative ELISA results were confirmed independently by PCR. The efficacy of Ribavirin in elimination of ACLSV was increased by increasing the concentration of cytokinin in the medium in parallel with decreasing the concentration of Ribavirin. These results are discussed in the context of the reliability of in vitro virus testing.