Shoots on interstem-dwarfed apple (Malus domestica Borkh.) trees ceased growing earlier and showed a stronger tendency towards becoming summer dormant than did corresponding shoots on vigorous trees. Substances similar to gibberellic acid (GA3) and abscisic acid (ABA) were extracted from 1-year-old stems at 7 stages during the growing season using the centrifugation technique. ABA-like activity was higher in stems from dwarf than vigorous trees at full bloom, and remained higher until after the onset of summer dormancy. GA-like activity also was significantly higher in dwarf tree stems at the tight flower cluster stage. Injection experiments demonstrated that increasing ABA concn decreased terminal elongation in a linear manner. ABA-induced inhibition was reduced in direct proportion to the concn of GA3 in the injected solution.
Four Malus dwarfing rootstock clones showed a range of rooting success when propagated as layers. Root emergence was largely confined to a nodal position near lateral buds. Anatomical studies revealed nodal rooting to be closely associated with the parenchymatous bud and leaf gaps of the stem. The highest starch concentration was in these tissues and the outer ring of pith cells. Etiolation during layering increased stem starch and decreased the degree of sclerification of the cortex. Rooting success was negatively correlated with degree of sclerification. Etiolated stem cuttings rooted in 7 days under mist propagation, while non-etiolated cuttings failed to root, indicating that etiolation provided a stimulus to root initiation in the non-differentiated, starch-rich gap areas. Inter-relationships of stem etiolation and internal carbohydrate reserves were associated with the rooting process.
Orchard performance over a 12-year period of ‘Delicious’ and ‘Jonathan’ dwarfed with M.8 interstems of different lengths (10, 20 and 30 cm) on Alnarp-2 clonal rootstocks influenced vigor, yield, and annual shoot growth. ‘Delicious’ required longer interstem material for adequate tree size reduction than did ‘Jonathan’. The total yields, based on one tree spacing treatment, were higher the first 6 years from interstem trees than from standard trees, followed by higher yields of standard trees in subsequent years. Projected closer tree spacings according to tree vigor as produced by different interstem lengths suggested that yields per hectar of ‘Delicious’ could be quadrupled and ‘Jonathan’ tripled when compared to standard trees.
Water suspensions from seeds, root and shoots of peach (Prunus persica (L.) Batsch) influenced growth of peach, apple and bean seedlings when applied to soil of potted plants. Different levels of amygdalin were found in plant parts of peach and apple. Synthetic amygdalin applied to potted peach seedlings was not toxic. Certain nutrient elements were altered due to the soil treatment. Disposal of plant parts is suggested as a practical sanitation practice to possibly reduce peach tree decline on old soil.