Source-sink relations in fruits .9. Effects of root treatments on growth and fruit development in apple trees

Root pruning experiments were carried out in the field as well as in well fertigated pots, in the latter case replanting into larger pots was also included and trees of different crop loads participated. Shoot growth was reduced in both cases, the same applied to remaining top parts in the pots and to fruit size in the field experiment. In pots root pruning and replanting increased fruit size slightly, and concentration of total dry matter, soluble solids and titrateable acids decreased. Effects on fruit size were promoted at a low fruit/leaf-ratio. Root pruning enhanced the development of new roots in pots. As a whole, effects of availability of assimilates dominated over effects of root treatments, negative correlations existed between fruit/leaf-ratio and fruit size, concentration of total dry matter, soluble solids, titrateable acids and root dry matter, respectively. It is suggested that the effect af root pruning depends on the reduction of the root size, and a subsequent counteracting effect connected to development-and activity of new roots. The latter is promoted at conditions with ample water and nutrient supply as well as at assimilates readily available for root growth. In certain cases this latter effect may equalize or even overrule the initiating effect of reducing the root size.