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  • Author or Editor: John McGuire x
  • Journal of the American Society for Horticultural Science x
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Abstract

The level of endogenous root-promoting and inhibiting substances in 3 clones of rhododendron were compared at seasonal intervals in order to study the clonal and seasonal variation in rooting response of cuttings. The highest levels of 4 rooting cofactors in any season were found in both stem and leaf tissue of Rhododendron cv. ‘Cunningham’s White’ followed by ‘English Roseum’. The clone ‘Dr. H. C. Dresselhuys’ contained the least amount of the rooting cofactors. An inhibitor was often found in all clones, but it appeared less responsible for clonal differences in rooting response than variation in levels of the rooting cofactors. Rooting cofactor levels contained in the stem tissue of ‘Cunningham’s White’ were not less than those in the leaf tissue. In contrast, cofactor levels present in the stem tissue of ‘English Roseum’ and ‘Dr. H. C. Dresselhuys’ were less than those in the leaf tissue. The promoting activity of rooting cofactors in all tissues of the clones increased in September and decreased again in November to the level of July extract. The inhibitor found in the July extracts disappeared in September and reappeared in November.

Rooting of cuttings of ‘Dr. H. C. Dresselhuys’ was significantly improved by grafting a leaf and bud scion of ‘Cunningham’s White’. On the other hand, scions of ‘Dr. H. C. Dresselhuys’ resulted in decreased rooting of cuttings of ‘Cunningham’s White‘. Rooting capacity of ‘English Roseum’ was less affected by a leaf and bud scion of other clones of Rhododendron.

Open Access

Abstract

A method of extracting indole compounds from stem segments of woody cuttings of Ilex crenata ‘Convexa’ by refrigerated centrifugation has been developed. Effective extraction was obtained when segments were immersed in a solution of 40% ethanol (v/v) and exposed to a force of 2750 X g for at least 2 hr. Exposure to that force for more than 4 hr did not result in a significant increase in extractable auxin. Quantitative determinations of 14C measured by liquid scintillation counts of the extracts revealed that this method reliably depicted changes in levels of IAA or its metabolized forms in different stem segments as a result of different treatments. Chromatographic separation of extracts revealed that at least 35% of the label was still in the form of IAA after 48 hr. The increased levels of auxin in stem segments was also portrayed by significant rooting increases as determined by rooting index. Centrifugation extracts separated into 2 phases and were removed separately, most of the isotope was contained in the smaller lower phase. Proportionate levels of the 2 phases changed in segments over time and the lower phase disappeared at the time of rooting.

Open Access

Abstract

Changes in levels of IAA in stem segments of Ilex have been detected by centrifugation extraction and subsequently identified by Rf. The radio-chemical was absorbed through intact tissue, leaf scars, wounds, or cut apical or basal ends of cuttings. It was not as readily transported to the base when it entered apical tissue through leaf scars as when it entered intact tissue of that region. When it entered basal ends of cuttings, some of it was carried to the apex within 48 hr.

Open Access