Changes in Endogenous IAA during Rooting of Hardwood Cuttings of Grape, 'Muscat Bailey A' with and without a Bud

The effect of disbudding on rooting and endogenous IAA in 'Muscat Bailey A' grapevine cuttings was investigated. Disbudding completely inhibited rooting of grapevine cuttings. More diffusible IAA was found in disbudded cuttings than in cuttings with one bud. The level of extractable IAA in the basal part where adventitious roots appear was significantly higher in the 1-bud cuttings than in disbudded cuttings 10 to 15 days after planting. It is assumed that during this period, root primordia are formed. Conversely, the applications of IBA and NAA to the disbudded cuttings induced root formation. However, the daily trends of endogenous IAA, especially that of extractable IAA, differed between the IBA and NAA treatments. Extractable IAA of disbudded cuttings treated with NAA increased for 20 days after planting, whereas in cuttings treated with IBA, there was no increase, the trend being similar to that of the control cuttings. These re-sults indicate that in the process of root formation in grapevine cuttings, a difference ex-ists between IBA and NAA action. It is also assumed that disbudding eliminated the source of extractable IAA which, therefore, inhibited rooting.