Salinity Tolerance of ‘Valencia’ Orange Trees on Allotetraploid Rootstocks

Resumen

A significant effort at UF/CREC has been the production of allotetraploid rootstock selections by somatic hybridization, and more recently by conventional breeding at the tetraploid level using selected somatic hybrid parents. In a greenhouse study, we determined responses to salinity stress (50 mM NaCl ~4,400 ppm TDS) of well-fertilized 1-year-old ‘Valencia’ orange trees on 18 new allotetraploid citrus rootstock selections and on the relatively salt sensitive Carrizo citrange rootstock with and without salinity stress for comparison. There were six replicate trees per treatment. After 5 months, all trees were visually rated from 1 to 10 for appearance in terms of phytotoxicity symptoms and leaf loss. Leaf chlorophyll was estimated using a SPAD meter on fully expanded mature leaves, which were then briefly rinsed in deionized water, oven dried, and used to determine leaf Na+ and Cl–concentrations. Overall, leaf Na+ and Cl− were strongly related but low SPAD values and low appearance ratings were more strongly correlated to high leaf Cl− than to high leaf Na+. Three allotetraploid zygotic hybrids from crosses of allotetraploid somatic hybrids (“tetrazyg”) rootstock selections (denoted O3, O4, and S11) were able to exclude Na+ and Cl− ions from ‘Valencia’ leaves better than most other rootstocks while maintaining good growth with no phytotoxic symptoms. These three tetraploid hybrid rootstock selections merit further evaluation of salinity tolerance and horticultural performance in the field.