The effects of 19 rootstocks on growth, cropping and mean fruit mass of the 'Rubin' apple trees in fertile soil were investigated in the years 2001-2006. Six years after planting, the trunk cross-sectional area (TCSA) was the largest on P 62, M.9 EMLA and Arm 18, and the smallest on PJ 629 (No. 629), J-TE-G, PB-4, P 59 and No. 280. The highest cumulative yields per tree were obtained on the most vigorous rootstocks as well as on B 491, P 16, P 63 and P 65. Trees on the latter four root- stocks gave the highest yields per hectare. Trees on P 66 could also be very productive if they were planted at the right density, adequate to their tree size. Trees on P 59, No. 280, P 22, PB-4 and J-TE-G showed a high yield efficiency (expressed as a ratio of cumulative yield to the final TCSA); however, due to the small tree size their yield per area unit was lower. Mean fruit mass for the 5 -year period was not significantly influenced by the rootstocks. The exception was PJ 629 which produced the smallest fruits.
We examined the effects of cooling applied for 4 to 20 weeks on donor cultures of four dwarfing apple rootstocks (P16, P22, P59 and M26). Our aim includes increasing their competence for in vitro adventitious shoot regeneration from the leaves. Donor cultures were maintained on a shoot multiplication medium at 4℃ in the dark for 4 months, followed by subculture on a fresh medium for 4 weeks. The cooling of the cultures caused an increase in the adventitious shoot number and a decrease in the starch content and an increase in the soluble sugar content (monosaccharides, raffinose and stachyose). The accumulation of stachyose in response to cold is a new observation, and it suggests that raffinose and stachyose play important role in the acclimation of dwarf apple rootstocks to low temperatures.
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