Potato virus Y strain spectrum in New Zealand - absence of recombinant N:O strains

Potato virus Y (PVY) is a serious plant pathogen, causing severe yield losses worldwide on members of the Solanaceae, including potato, pepper, tomato and tobacco. During the last two decades new virus strains have been detected, including those representing recombinants between N- and O-strains, now designated PVYNTN and PVYN-Wilga, respectively. The question of whether recombination is easily induced in nature by mixed infections of potato might be answered by an investigation of strains appearing under isolated conditions such as those in New Zealand. More than 30 PVY isolates collected during the last 20 years were characterized biologically, serologically and using molecular biological approaches. The New Zealand population of PVY isolates was mainly composed of PVYN and PVYO. To date no recombinant strains have been found among the isolates tested. Similarly, experiments performed with these isolates on potatoes under greenhouse conditions with mixed infection PVYN/PVYO did not result in signs of recombination. This raises the question as to the driving force for the appearance of recombinant strains. It also demonstrates the efficacy of plant quarantine measures in New Zealand over the past 20 years.