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  • Author or Editor: Tom Mock x
  • Journal of the American Society for Horticultural Science x
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In Coprosma baueri Endl. low response to foliar sprays of 1% daminozide (SADH; succinic acid 2,2 dimethyl hydrazide) was accounted for, in part, by low levels of endogenous SADH in the terminal shoot tissues. The same exogenous application rates to Xylosma congestum (Lour.) Merr. and Pyracantha coccinea Roem. caused greater inhibition of stem elongation and higher endogenous levels of SADH. However, the most significant results of this study were that a negligible relationship existed between level of SADH in tissues of elongating branches and the inhibition of stem elongation. Elongation did not increase in stems of Xylosma, Coprosma and Pyracantha after 60 to 90 days even though endogenous SADH concentration decreased sharply in this interval. We concluded, therefore, that only a portion of the SADH found in tissues was active in inhibiting stem elongation. Multiple applications of SADH, made after pruning but before branch elongation had begun, caused greater inhibition of elongation than was expected on the basis of endogenous levels of SADH. This response suggested that exogenous applications reached sites in axillary buds critical for inhibition of elongation more readily than endogenous SADH translocated from older leaves. The implications of these findings for interpreting comparative activity studies among analogs of growth retardants and among species is discussed.

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