2018 ASHS Annual Conference

This study investigated the influence of root substrate composition and container volume on the growth of apple rootstock plants propagated by tissue culture. Rooted dwarf apple rootstock (M-9) plants (15±1 cm tall) grown from shoot tip cultures and acclimated were transplanted into cell packs containing various ratios of peat moss (PM), vermiculite (VL), and perlite (PL) and cultured for 11 weeks in a greenhouse. For the study of root substrate composition, 3 different mixtures (1:1:1, 1:2:3, 3:1:2 mixes of PM:VL:PL by volume) were contained in plug trays (7.5 cm diam., 16 cm deep round cell packs, one plant per cell). For the substrate volume study, stock plants were grown in cell packs containing 300(φ5.5cm, H17cm), 500(φ7.5cm, H16cm) and 1000ml(φ13cm, H10.5cm) of 1:1:1 mixture of PM, VL and PL. During the experiment, the greenhouse temperature, humidity, and light intensity were 30±5℃, 72±5% RH, and 150±10 µmol·m^-2·s^-1, respectively. Plants were irrigated weekly with a weak nutrient solution (EC 1.3 mS/cm) using a dripper and sprayed over twice a day with tap water using an atomizer. After 11 weeks of culture, the plant height (70-78 cm) and stem diameter (4.2-4.5 cm) measured at 30 cm above ground, leaf chlorophyll content (SPAD) and photosynthetic rate were unaffected by variation in media composition. However, the number of nodes and leaves as well as shoot fresh and dry weights were greater when plants were grown in the 3:1:2 mixture of PM:VL:PL, compared to those grown in the 1:1:1 mixture. While SPAD readings and plant heights (66-74 cm) were unaffected by root substrate volume, the number of nodes, root length, shoot and root fresh weights of the plants grown in the 1000 ml volume were the highest compared to those grown with 500 ml or 300 ml root substrates. However, plants grown in 1000 ml substrate had a lower photosynthetic rate than those grown in smaller substrate volumes. The stomatal conductance and transpiration rate were unaffected by root substrate volume. In conclusion, the initial growth and development of the tissue culture propagated M-9 apple rootstock plants were more favorable when grown in 1000 ml of the 3:1:2 mixture of PM:VL:PL in comparison to other treatments.