Salinity effects on `Hass' avocado was studied on three rootstocks, `Thomas' (TH), `Toro Canyon' (TC), and `Duke 7' (D7). Four levels of salinity (1.4, 3.0, 4.5, and 6.0 dS·m–1) were applied to 1-year-old trees grown in sand culture for 10 weeks. Increased salinity resulted in decreased trunk cross-sectional area and reduced shoot growth. Specific leaf area and dry weight decreased linearly with increased salinity. TH was significantly more affected than TC of D7. Leaf necrosis was also greatest in TH. Older leaves had the highest percentage of leaf necrosis, while younger leaves of TH exhibited symptoms only in the 6.0 dS·m–1 treatment. TH had the highest Cl leaf levels. TC maintained the lowest Na levels in the scion plant organs, indicating an ability to sequester Na in the rootstock. TC also had the lowest Na:K ratio in leaf tissue, indicating that TC can utilize K as an osmoticum. Predawn xylem potential decreased linearly with increased salinity in all rootstocks. Leaf osmotic potential decreased with increased salinity; however, leaf age moderated the response, indicating an adjustment to the stress. No rootstock differences were observed. Net CO2 assimilation (A) decreased with time only in trees exposed to 4.5 or 6.0 dS·m–1. Reduction in A due to increased salinity was less in younger leaves. No rootstock differences were noted. Chlorophyll per leaf area decreased with increased salinity to the greatest degree in TH.
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