The issue of the influence of rootstock on winter-hardiness of plum (Prunus × rossica Erem.) tree flower buds in the Baltic region is becoming important. The choice of rootstock is the main precondition for obtaining a high yielding and sustainable plum orchard. Freezing of flower buds is one of the most significant damages in winter for stone fruits. The aim of the investigation was to determine the relationship between concentration of dry matter and reducing sugars in annual shoots during winter and wintering ability of trees. The dynamics of reducing sugar concentration in one-year-old shoots during winter was investigated during two successive seasons in two locations. Orchards were planted in 2001 in Latvia and in Estonia. The well-known plum cultivar ‘Kubanskaya Kometa’ (Prunus rossica Erem.) was grafted on eight clonal rootstocks (‘St. Julien A’, ‘Brompton’, ‘Ackermann’, ‘Pixy’, GF8/1, G5/22, GF655/2, and ‘Hamyra’) and eight generative propagated rootstocks (‘St. Julien INRA 2’, ‘St. Julien d’Orleans’, ‘St. Julien Noir’, ‘Brompton’, ‘Wangenheims Zwetsche’, ‘St. Julien Wädenswill’, ‘Myrobalan’ and Prunus cerasifera var. divaricate). Shoot samples were harvested two times during winter — at the end of January and at the end of March. Dry matter concentration (mg·g−1) and the concentration of reducing sugars (mg·g−1 DM) by Fehling’s solution method was determined. Tree flowering intensity was scored using a scale from 1 to 5, where 1 = no flowers and 5 = abundant flowering. Dry matter concentration in plum shoots varied among rootstocks, years and growing location. In Pūre, Latvia, the largest differences in dry matter concentration were found for trees grafted on ‘St. Julien INRA2’ (in 2011–2012) and ‘Brompton’ cuttings (in 2012–2013) but in Polli, Estonia for trees grafted on G5/22 (in 2011–2012) and ‘Myrobalan’ (in 2012–2013). One of the most stable rootstock/graft combinations in the trial when GF655/2 was used as rootstock, where dry matter concentration was between 491 and 525 mg·g−1, and reducing sugars between 37.5–49.2 mg·g−1, and flowering intensity between 2.5 and 4.
The lack of suitable plum rootstocks for Baltic conditions has become a problem during recent years due to changing climatic conditions. Rapid temperature fluctuations between freezing and thawing are occurring more frequently. The winter-hardiness of rootstocks is essential for overwintering of trees in such conditions. The content of accumulated reducing sugars is an important physiological factor influencing wintering ability of trees. The dynamics of reducing sugars was investigated during two winter seasons (2010/2011 and 2011/2012) in one-year-old ‘Kubanskaya Kometa’ (Prunus x rossica Erem.) hybrid plum shoots from two orchards planted in 2001 at Pūre Horticultural Research Centre (Latvia) and Polli Horticultural Research Centre (Estonia). Cultivar ‘Kubanskaya Kometa’ was grafted on eight clonal rootstocks: ‘St. Julien A’, ‘Brompton’ cuttings, ‘Ackermann’, ‘Pixy’, GF8/1, G5/22, GF655/2, ‘Hamyra’ and eight seedling rootstocks: ‘St. Julien INRA 2’, ‘St. Julien d’Orleans’, ‘St. Julien Noir’, ‘Brompton’ seedlings, ‘Wangenheims Zwetsche’, ‘St. Julien Wädenswill’, ‘Myrobаlan’ and Prunus cerasifera var. divaricata. Trees were planted at 5×3 m spacing in four replications per rootstock with three trees per plot. Shoot samples were harvested five times during the winter period. The concentration of reducing sugars (mg g-1 dry weight) was determined with Bertran’s method. Significant differences in concentration of reducing sugar were found between samples coming from different locations and in two seasons. The maximum concentration of reducing sugar was found in December or January depending on growing location and meteorological conditions
The selection of appropriate rootstock is the main precondition for obtaining a high yielding and sustainable plum orchard. In the Northern climate, plum overwintering is especially important, where winter hardiness of flower buds is one of indicators. This investigation was carried out during three wintering periods (2010–2013) at the Institute of Horticulture in Pūre (Latvia) and the Polli Horticultural Research Centre (Estonia), in orchards planted in 2001. The aim of the investigation was to evaluate the influence of different rootstocks on the viability of flower buds during winter for two plum cultivars in two growing regions. European plum ‘Victoria’ and hybrid plum ‘Kubanskaya Kometa’ grafted on eight clonal and eight seedling rootstocks were used in the investigation. Bud samples were taken two times during winter: end of January and end of March. The viability of flower buds and flowering intensity were determined in the laboratory. The viability was determined as dehydrogenase activity using triphenyl tetrazole chloride (0.5%), where in living cells the colourless substance due to enzymatic activity turns into a brightly coloured product — formasan. The optical density of colour was determined with a spectrophotometer at 485 nm. Both cultivars ‘Kubanskaya Kometa’ and ‘Victoria’ had higher flower bud viability in Polli compare to Pūre. In both growing regions, the highest activity of dehydrogenases for cultivar ‘Kubanskaya Kometa’ was on rootstocks ‘Myrobalan’, ‘St. Julien INRA 2’, ‘Wangenheims Zwetsche’ and for cultivar ‘Victoria’ — on rootstocks ‘Ackermann’, ‘Brompton’ seedlings, and ‘St. Julien d’ Orleans’. The dehydrogenase activity of in flower buds had a tendency to decrease during winter.
The aim of the investigation is to evaluate the influence of different rootstocks on the flowering intensity of two plum cultivars: a hybrid `Kubanskaya Kometa` and European plum ‘Victoria’ in diverse locations. Sixteen well known European rootstocks were used, of which eight were clonal (St. Julien A, Brompton, Ackermann, Pixy, GF8/1, G5/22, GF655/2, Hamyra) and eight were seedlings (St. Julien INRA2, St. Julien d Orleans, St. Julien Noir, Brompton, Wangenheims Zwetche, St. Julien Wädenswil, Myrobalan, P. cerasifera var. divaricata). The evaluation was conducted in experimental orchards which were established in spring 2001 in Latvia, Estonia and Belarus. Trees were planted at a spacing of 5 × 3 m in four replications, three trees per plot. The obtained data from the years 2008-2012 are presented. The flowering intensity of plum trees depended on the cultivar rootstock combination. The influence of rootstock on flowering intensity differed between the years and growing region, and was closely correlates with meteorological conditions during the wintering period. Cv. ‘Kometa Kubanskaya’ had the highest blooming intensity in Pûre on rootstocks GF 655/2 and Wangenheims Zwetche; in Brest on Brompton seedlings, Julien d’ Orleans G5/22 and Ackermann; and in Polli on GF 8/1 and Brompton seedlings. ‘Victoria’ plum trees had the highest intensity of flowering on rootstocks Pixy and Wangenheims Zwetche in Pūre; on St. Julien INRA 2 and Ackermann in Brest; and on GF 655/2 and Ackermann in Polli.
Proper selection of rootstock that is adapted to local growing conditions and climate is one of the most important preconditions for obtaining high yield in intensive plum orchards. The aim of the investigation was to evaluate the influence of different rootstocks on the productivity of two plum cultivars: ‘Kubanskaya Kometa’ (Prunus rossica. Erem.) and ‘Victoria’ (P. domestica L.) in different climatic conditions. The following sixteen rootstocks known in Europe were used in the trial: eight vegetatively propagated (‘St. Julien A’, ‘Brompton’, ‘Ackermann’, ‘Pixy’, ‘GF 8/1’, ‘G 5/22’, ‘GF 655/2’, ‘Hamyra’) and eight generatively propagated (‘St. Julien INRA2’, ‘St. Julien d’Orleans’, ‘St. Julien Noir’, ‘Brompton’, ‘Wangenheims Zwetsche’, ‘St. Julien Wädenswil’, ‘Myrobalan’, P. cerasifera var. divaricata). The evaluation was made in experimental orchards in Latvia, Estonia and Belarus. Orchards were established in spring 2001. Trees were planted at spacing 3 × 5 m in four replications, three trees per plot. The data obtained in years 2008-2015 are presented. The yield was influenced by rootstock and differed between years, growing regions and cultivars. The meteorological conditions during wintering period had significant influence on yield for trees on all evaluated rootstocks.