THE RELATIVE TOLERANCE OF 6 PRUNUS ROOTSTOCKS TO BORON AND SALINITY

The influence of B and salinity [3 Na2SO4:1 CaCl2, (molar ratio)] on B toxicity and the accumulation of B, sodium, and SO4 in six Prunus rootstocks was evaluated. High salinity reduced B uptake, stem B concentrations, and the severity of toxicity symptoms in five of the six rootstocks. Forward and backward stepwise regression analyses suggested that stem death (the major symptom observed) was related solely to the accumulation of B in the stem tissue in all rootstocks. The accumulation of B and the expression of toxicity symptoms increased with time and affected rootstock survival. No symptoms of B toxicity were observed in leaf tissue. The Prunus rootstocks studied differed greatly in stem B accumulation and sensitivity to B. The plum rootstock 'Myrobalan' and the peach-almond hybrid 'Bright's Hybrid' were the most tolerant of high B and salinity, whereas the peach rootstock 'Nemared' was very sensitive to high B and salinity. In all rootstocks, adding B to the growth medium greatly depressed stem SO4 concentrations. In every rootstock except 'Nemared' peach, adding salt significantly depressed tissue B concentrations. A strong negative correlation between tissue SO4 and B was observed. Grafting experiments, in which almond was grafted onto 'Nemared' peach or 'Bright's Hybrid', demonstrated the ability of rootstocks to influence B accumulation and scion survival.