Physiological Effects of Salinity Stress On Grafted and Non-Grafted Trees.

As climate change impacts rainfall distribution and frequency many agricultural producers are turning to alternative water sources as supplemental irrigation.  Often these sources are of low quality and high in salinity.  Glycophytic crops, which include most agricultural crop species, are negatively impacted by salt stress.  This results in a dramatic decrease in yield and quality when salt is present in the soil.  Citrus, a salt sensitive crop, tolerates less than 2 dS m^-1 of salt before yields are reduced.  Sour Orange (SO) is a common rootstock used in the citrus industry, however, it is susceptible to Citrus Tristeza Virus (CTV) which has led to the decline of its use in recent years.  Several newer rootstock varieties are CTV resistant; C22 and C146 rootstocks are among the most promising but have not been tested for their salinity tolerance.  The objectives of this experiment were to determine the impacts of salinity on grafted and non-grafted citrus rootstocks by taking physiological measurements over time.  In this experiment, saline irrigation water was applied at 0, 1, 3, 5, and 10 dS m^-1 to grafted and non-grafted trees over a period of 6 months.  Results showed that grafting reduced salinity tolerance of citrus rootstocks as shown by reduced growth, increased membrane permeability, and lower chlorophyll fluorescence values.  Membrane permeability increased as a result of both grafting and salinity, but less dramatically in non-grafted rootstocks.  C146 non-grafted rootstocks showed the least membrane leakage at 10 dS m^-1, with 34.8% electrolyte leakage.  Membrane stability and chlorophyll fluorescence were also negatively affected by the time exposed to salinity stress.  Experimental results indicate that non-grafted rootstocks had higher salinity tolerance as grafting significantly reduced salinity tolerance in all rootstock varieties evaluated.