Effect of 2,4-Dichlorophenoxyacetic Acid (2,4-D) on the Size of the Navel end Opening of Navel Oranges-A Preliminary Study

摘要

Large,protruding navels of navel oranges are a major cull factor in the packhouse. Previous work on navel orange trees suggested that the synthetic auxin,2,4-dichlorophenoxyacetic acid (2,4D) applied at full bloom at 20mg/L reduced the diameter of the navel end opening and increased the percentage of closed navel ends,with no effect on the number of fruit per tree or total yield. To examine the efficacy of 2,4-D in reducing navel end size under South African conditions and to determine if such a treatment would result in any detrimental effects on external and internal fruit quality, a preliminary study was undertaken. * Palmer' , * Robyn' and ' Lane Late' navel trees were sprayed with 2,4-D at 25mg/L at petal drop. At harvest,navel end size,and external and internal fruit quality were evaluated. Application of 2,4-D to ' Palmer' navel trees increased the percentage of closed navel ends and decreased average navel end size,with no effect on fruit length,fruit shape or rind thickness. Treated fruit had slightly coarser, greener rinds and greener navel ends. There was no major negative effect on internal fruit quality, although the slight reduction in total soluble solids (TSS) and juice percentage in treated fruit may be of commercial importance. No granulation or thicker pedicels were observed in any of the fruit sampled. Other negative treatment effects include curled leaves of the spring flush. Similar results on navel end size and fruit quality were observed on fruit from 2,4-D-treated ' Robyn' and ' Lane Late' trees. Treatment with 2,4-D shows potential to reduce navel end size of navel oranges, especially if the detrimental effects can be eliminated or reduced.