Growth and physiological responses of young olive trees affected by Olive leaf yellowing associated virus

We studied the effect of Olive leaf yellowing associated virus (OLYaV) on biometric and physiological changes in olive. The trial was carried out on 32 two-yearold virus-free trees of 'Frantoio' grafted on virus-free olive seedlings and grown in 32-L pots. Half of the trees were inoculated with OLYaV in the fall of 2007. At 6, 18, and 24 months after inoculation, tree height, basal trunk diameter and total leaf number were determined, and leaf area tree-1 was estimated from a 50-leaf subsample. Twigs of various order were also counted and measured. At the end of the experiment, dry matter partitioning, leaf gas exchange and water potential were also measured. Total twig length and number, trunk diameter and leaf area were significantly reduced by OLYaV, whereas no effect was detected on tree height. Water potential was lower in virus free trees due to a greater leaf area; gas exchange rates were proportional to water status. Trees affected by OLYaV partitioned more dry matter to roots and less to the main stem compared to virus-free trees. The growth reductions could not be explained by differences in water relations or assimilation, but may relate to the sink's ability to attract and/or use assimilates.