In 2001, investigations were carried out on the Latvian origin cultivar ‘Suvenîrs’ grafted on seven pear rootstocks (MA, MC, BA29, Pyrodwarf, Brokmal, Kirchensaller Mostbirne and Kazrauðu bumbiere) in Polli (Estonia), Pûre (Latvia) and Babtai (Lithuania). The aim of the investigation was to evaluate pear rootstocks in different climatic conditions in the Baltic region. In Polli, all trees were planted in a dense planting, and therefore, trunk cross section area did not differ significantly between trees on different rootstocks. The most vigorous tree habit was observed in Lithuania for trees grafted on the rootstocks Kirchensaller Mostbirne and Brokmal, but in Latvia on Kirchensaller Mostbirne and Kazrauðu bumbiere. The highest dwarfing effect was observed for rootstock MC in both places. The highest cumulative yield from the orchard area was found for trees grafted on rootstocks of the quince group in all three locations of investigation. Nevertheless, the winter hardiness of the quince group rootstocks was not sufficient for Baltic climatic conditions. Good overwintering in Latvia and Lithuania was observed for trees on Pyrodwarf. Survival rate of trees grafted on Pyrodwarf in Estonia was unsatisfactory. The worse overwintering in Lithuania was observed for trees grafted on Brokmal. There was a dwarfing effect on trees and better yield on the vegetative propagated rootstocks included in the investigation, but none one of them can be recommended as perspective for commercial orchards in Baltic agro-climatic conditions.
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 development of new environmentally friendly plant protection products against grey mould disease (caused by Botrytis cinerea Pers.) was started in 2010. In the Latvian State Forest Research Institute “Silava”, production of coniferous biomass extracts using different solvents for extraction was performed. During 2010-2011, several laboratory investigations were carried out in the Institute of Biology, University of Latvia. Effectiveness of pine (Pinus sylvestris) and spruce (Picea abies) biomass extracts against Botrytis cinerea was tested. On the basis of coniferous extracts, 11 formulations were created and characterised. The effect of the formulations on mycelial growth of B. cinerea test cultures was tested using the fungal radial growth test. All formulations had inhibitory effect on mycelium growth (inhibition rate over 50%) at concentration 20 g L-1 in medium. The impact of formulations on plants after spraying was evaluated using in vitro propagated strawberry plants. Chlorophyll content and chlorophyll fluorescence were estimated. Extracts did not show negative effect on the chlorophyll content and fluorescence of strawberry leaves. Field investigations on strawberry (Fragaria × ananassa Duch.) ‘Senga Sengana’ and primocane raspberry (Rubus idaeus) ‘Gerakl’ were conducted in the Pûre Horticultural Research Centre in 2011. None of tested the coniferous biomass extract formulations showed higher effectiveness than fungicide Signum® (pyraclostrobin 6.7%+ boscalid 26.7%, BASF).