Analysis of the main factors involved in the evaluation of Prunus resistance to Plum pox virus (Sharka) in controlled greenhouse conditions

In countries like Spain or France, quarantine rules force researchers to evaluate the resistance to Sharka (Plum pox virus, PPV) in controlled, isolated conditions. This evaluation method shows important limitations resulting from the management of plants in the controlled conditions, grown in pots with artificial cycles of growth in the greenhouse and cold chamber, alternately. The objective of this study is to analyse different factors that affect the efficiency of the method of evaluation of PPV resistance in controlled greenhouse conditions. The cultivars evaluated as model genotypes were the resistant ‘Stark Early Orange’ and the susceptible ‘Real Fino’ apricot. Furthermore the ‘GF305’ peach was used as a susceptible control. The different studied factors were the inoculation protocol (rootstock or variety inoculation), the grafting success (depending on inoculation method, rootstock–variety combination and date of grafting), and the efficiency of the process in each artificial cycle of growth. Results showed that rootstock inoculation was more effective than inoculation of the variety. As rootstock, the ‘GF305’ seedlings were slightly better than the ‘Real Fino’ seedlings in the inoculation process, but they were quite similar in terms of effectiveness in the evaluation and grafting process. Grafting can be carried out in spring or autumn without having important differences. The global efficiency of the evaluation process was much higher with rootstock inoculation.