EFFECTS OF FRUITING ON THE GROWTH OF APPLE TREES ON FOUR ROOTSTOCK VARIETIES

Abstract

Worcester Pearmain apple trees on four rootstock varieties with a range of vigour were grown in pots for 3 years. The effects of fruiting, determined by comparison with deblossomed trees, were qualitatively similar on all the rootstocks. The growth of all parts, particularly the roots, was less on fruiting trees. The greatest differences occurred in trees on the very dwarfing 3426 rootstock which bore the largest crops relative to the size of the tree; their root systems were severely reduced. When differences in fruitfulness were taken into account, the quantitative effects of fruiting on the dry weight increment of the combined perennial parts, and of the roots alone, were apparently the same on all the rootstocks. Trees with low levels of fruitfulness produced less dry matter, including fruit, than deblossomed trees because of lesser shoot growth. Trees of high fruitfulness produced as much, or even more dry matter than deblossomed trees because of increased photosynthetic efficiency. Comparisons of the shoot growth and stem‐to‐root ratios of the deblossomed trees on each rootstock variety indicated that the hypothesis put forward in a previous paper to explain the dwarfing mechanism of M.1X may be valid for 3426 also. Copyright © 1970, Wiley Blackwell. All rights reserved