SHOOTS FROM MM-106 APPLE ROOTSTOCKS GROWN IN A POLYTHENE TUNNEL DO NOT CONTAIN A HIGHER IAA CONCENTRATION THAN SHOOTS FROM FIELD-GROWN PLANTS

MM. 106 apple rootstock plants grown in a polythene tunnel show greate r apical dominance and a higher propensity to root as cuttings than pl ants grown in the field. Experiments were conducted to test the hypoth esis that the growth habit and rooting behaviour of polythene tunnel p lants were caused by increased concentrations of indole-3yl-acetic aci d. Cuttings taken from field-grown plants which had been sprayed with IAA showed increased rooting. In shoots of both field-grown and polyth ene tunnel-grown plants endogenous IAA levels were highest in the uppe r shoot region and declined progressively with distance from the apex. plants grown in the polythene tunnel, however, did not contain signif icantly higher IAA levels than field plants. The analytical data do no t support the hypothesis that the growth and rooting behaviour of plan ts grown in a polythene tunnel were caused by increased concentrations of IAA.