Salt-stress effects on avocado rootstock growth. I. Establishing criteria for determination of shoot growth sensitivity to the stress

The mechanisms of shoot growth inhibition under salt-stress are not yet und erstood. Comparative evaluation of growth tolerance level of plant material used for mechanistic studies into stress effect on growth processes is a c ritical step towards establishing a plant model system for studies of stres s effects on growth. In the present study, numerous vegetative shoot-growth parameters were eval uated as criteria for determination of shoot growth sensitivity of avocado rootstocks ( Persea americana Mill.) to salt-stress. Seven different West-I ndian rootstocks were investigated for their growth response to the stress. The plants, grown in 50 L soil-filled containers, were treated with 4 mM N a and 6 mM Cl (control) or 18 mM Na and 20 mM Cl (salt) for a period of 3 y ears. Changes in trunk diameter, branch diameter, number of new branches, b ranch fresh weight (FW) and dry weight (DW), leaf length, leaf area, leaf n umber, leaf FW and DW and distribution of the leaf population into size cla sses, were quantified during the season of rapid shoot growth, and used for grading growth sensitivity. The seven rootstocks studied were ranked according to the sensitivity of th eir vegetative growth to the stress. The order of sensitivity was found to be similar when the ranking was based on changes in DW and FW deposition pe r branch, cumulative leaf area and leaf weight per branch, or branch stem w eight. Stress effects on leaf FW deposition were similar to the effect on t otal branch FW. Stress effects on branch stem FW were closely related to to tal branch DW deposition. Inhibition of cumulative leaf area per branch was less sensitive to the stress than deposition of FW or DW biomass. Biomass production per branch, or alternatively leaf biomass production per branch, is suggested as a practical parameter for evaluation of avocado rootstock shoot growth sensitivity to salt-stress.