Morphophysiological response of young olive trees to verticillium wilt under different surface drip irrigation regimes

The effects of irrigation on verticillium wilt in olive, in terms of morphological, biomass and physiological parameters were evaluated on pot-grown trees maintained in the field for 3 years. Plants inoculated and noninoculated with Verticillium dahliae were irrigated to high and low range of soil water content (HR and LR) at daily (DF; about 2 days/event), weekly (WF) and daily-weekly (DWF) drip-irrigation frequency. Morphological parameters, relative biomass and biomass water-use efficiency were higher at LR than at HR (with few exceptions) and at DF than at other frequencies in noninoculated and inoculated plants, but the fungus reduced those parameters by 17.0–38.5%. Lower root weight ratio, relative biomass and shoot length as area originated at HR in noninoculated plants, could be favourable to the accumulation of root infections and the amount of fungus per tissue length in inoculated plants because higher infection was known at HR. Moreover, higher aerial biomass and length promoted by irrigation at DF could prevent the more severe expression of symptoms, which occurred at WF and DWF in the presence of Verticillium. Negative correlations were found between indicated parameters and disease. Lower water stress (SΨ), and higher stomatal conductance (gs) and net photosynthesis at DF in noninoculated plants could limit the disease by improving water status, as SΨ was increased by the fungus only at WF and DWF, and gs and disease were negatively correlated. LR-DF treatment minimized the disease and kept the growth, water-use efficiency and physiological parameters in inoculated plants to levels close to noninoculated plants.