Induction of feathers by growth regulators on maiden trees of apple and pear

Abstract

SummaryThe relationship between some physiological and hormonal aspects of the morphogenesis of the lateral shoots (feathers) has been investigated on apple and pear maiden trees.Bioassays of extracts from the upper part of Jonathan and Rhode Island Greening apple trees showed that the level of endogenous ‘promoters’ decreased in Jonathan (which tends to feather naturally) during the period of spring bud-break, while the level of ‘inhibitors’ appeared to be small but constant. In R. I. Greening (which does not feather easily) the levels of both promoters and inhibitors were higher and constant during the five weeks of the investigation. These data support the view that apical dominance is mainly related to the movement of auxins from the shoot apex to the regions below. Consequently the strong polarity of the shoots can be ascribed to the greater quantity of auxin-like substances and to the balance between these substances and inhibitors.The application of the anti-auxin TIBA induced feather formation in Starking Delicious apple and Passe Crassane pear (which do not normally branch freely), but its action also involved some negative effects on the anatomical and morphological pattern of the trees.In Golden Delicious and Starking Delicious apples and Comice and Passe Crassane pears, a large number of feathers without any phytotoxic symptoms was obtained by the use, in the nursery, of diphenylurea (DPU) at 500 and 1000 ppm and maleic hydrazide (MH) at 1300 ppm. These results suggest a possible approach for producing nursery trees that are more suitable for the two modern training systems known as ‘palmetta anticipata’ and ‘slender spindle’.