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Leaf and stem anatomy of several apple cultivars, their compact mutants, and alar treated plants. Liu, Alice Chen-Miao


Naturally occurring compact (spur type) apple trees (Malus sylvestris L.) were compared with standard and Alar treated trees. Stem anatomy received special attention because no comparisons had been done of the stem anatomy in standard and compact apple trees. Anatomical studies of leaves in compact mutants and in Alar treated Red Delicious are more detailed than in earlier reports. Four cultivars were used in the studies. They were Harrold Red Delicious, a compact mutant of Red Delicious, namely Starkrimson, and standard Golden Delicious, and its compact mutant Starkspur. There were three main studies in this investigation. In the first study, anatomical examinations were made on the four cultivars without Alar treatment. Starkspur Golden Delicious was found to have the thickest leaf and palisade parenchyma among the four cultivars studied. The compact type was found to have a thicker leaf, palisade parenchyma and greater mean palisade number when compared with the standard type. The effect of Alar at concentrations of 0 and 1000 ppm on the same cultivars was investigated in the second study. The suppression of terminal growth by Alar varied among the cultivars. The response to Alar was greatest with Starkspur and 50 per cent inhibition of shoot growth was observed. Starkrimson was not affected by Alar treatment. Microscopic examination revealed that there were no significant differences in cell length of collenchyma, parenchyma and pith cells or in cell diameters and tissue thickness when the samples were taken from the first internode under the growing tip. In study three, the effect of Alar and its interaction with gibberellic acid on Red and Golden Delicious were considered. In this study, comparisons were also made with the untreated compact mutants. Alar treatments of Red Delicious were found to increase thickness of total leaf, spongy parenchyma and the length of palisade cells. The latter two accounted for the increase in total thickness of Alar-treated Red Delicious leaves. Gibberellic acid stimulated the shoot growth of Golden Delicious and Starkspur by 29 per cent, but this stimulating effect was prevented by Alar.

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