Eleven plum cultivars (Prunus domestica L.) for processing grafted on semidwarf rootstock ‘Wangenheim Prune’ and vigorous rootstock ‘Myrobalan’ were densely planted (1000, 1250, 1666, 2500 trees ha-1) and trained to central leader spindle tree. A new training system was applied to obtain trees suitable for mechanical harvesting. The leader was not headed after planting and summer training procedures were performed in May/June. From the third year onwards, renewal pruning was carried out after fruit harvesting. The new training and pruning systems resulted in very fast tree growth, abundant branching, fruit bud formation on young wood and early bearing. The plum trees appeared to be suitable for hand and mechanical harvesting within 3 years from planting. The self propelled straddle combine harvester was able to harvest 2-3 tons of plums per hour compared to 30 kg with hand picking. Harvesting effectiveness was 90-95%. The quality of mechanically harvested plums was a little worse than of those hand picked, but fruits were suitable for processing. The ‘Common Prune’ and the prune type small plums were the most suitable fruit for mechanical harvesting.

Polyploidization is an important source of variability for plant breeding. Polyploids are often characterised by increased resistance to biotic and abiotic stresses. Since drought and pathogen attack are the main threats to apple cultivation, obtaining new sources of resistance is an important issue for apple breeding. The newly obtained autotetraploid clones of apple cv. ‘Redchief’ showed superior resistance to fire blight. The aim of the presented research was the in-depth phenotypic characterisation of ‘Redchief’ tetraploids and assessment of their response to drought at the physiological and genetic level. The growth of own-rooted five-year-old trees of ‘Redchief’ tetraploids was poor compared with diploids; all growth parameters—the number and length of current season shoots, the total length of current season shoots per tree and the cross-section area of the trunk—were reduced in tetraploid clones. Grafting on M9 rootstock improved the growth characteristics of ‘Redchief’ tetraploids. Compared with diploid plants, the leaves of tetraploids were thicker, with altered shape, higher chlorophyll content, and larger stomata, but the stomatal density decreased. The leaf anatomical structure of tetraploids was changed, the adaxial and abaxial epidermis and both types of mesophyll were significantly thicker than in diploids. Moreover, the pollen grains of tetraploids were larger, but their viability and germination were reduced. Under conditions of limited water supply, the reduction in growth parameters was smaller and the physiological parameters were higher in the ‘Redchief’ tetraploid clone 4x-25 than in diploid plants. The expression of APX gene was higher in tetraploids than in diploids 15 days after drought stress induction. The results suggest the enhanced drought tolerance of the studied ‘Redchief’ autotetraploid clone compared with its diploid counterpart.

To study possibility of protection of sweet cherry fruit against cracking several rows of ‘Lapins’ sweet cherry (Prunus avium L.) trees grafted on ‘Colt’ rootstock, spaced 5 × 2.5 m and trained to a central leader were covered with a plastic foil to a height of 5 m. Several rows were left uncovered as a control. In the years 2016 and 2018, sun irradiation, air temperature and fruit quality were evaluated. The plastic cover reduced solar irradiation under the tunnel roof by around 40%. Light distribution within tree canopies was depleted by roughly 50%, but in the lower parts of the tree canopies, it was reduced to 6%, which is below the critical level (20%) estimated for apple trees. These results indicate the necessity to remove the covers as soon as possible after harvesting. Mean daily temperature near the ground was lower under the covers than outside, but at the height of 4.0 m, daily mean temperature was 0.4 °C higher and mean temperature during midday hours was 1.5 °C higher. The plastic covering reduced the fruit cracking from about 20% to 2% in both seasons but did not affect the fruit yield. The plastic covering did not affect the firmness and antioxidant activity and total anthocyanin content, but in the year 2018, it reduced the mean fruit weight, soluble solid, titratable acidity, dry matter and total polyphenols content.

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The relation of hand-harvesting cost in plum and prune production to the total costs amounts to 25-40%. Mechanical harvesting makes it possible to cut drastically both the harvesting and total costs. To test the suitability of plum and prune species to be mechanically harvested, an experimental grove (area 0.8 ha) was established in 2008. Three plum cultivars and one prune cultivar grafted on semi-dwarf and vigorous rootstocks were planted at high density (1250; 1666; 2500 trees·ha−1). During the span of full yielding (2012-2014), fruits were harvested mechanically with a canopy contact, straddle harvester in continuous motion, designed at the Institute of Horticulture in Skierniewice, to harvest tart cherry, and later adapted to harvesting plums and prunes. Trees grafted on semi-dwarf rootstock (‘Wangenheim Prune’) appeared to be more suitable for mechanical harvesting than strong-growing trees grafted onPrunus cerasiferaclone ‘Myrobalan’. Cumulative yield per ha (years 2012-2014) was the highest at the highest planting density. Trees grafted on the semi-dwarf rootstock had a higher productivity index than trees grafted on the vigorous rootstock. There was no significant difference in fruit quality related to planting distance. Mechanical harvesting was nearly 40 times more efficient than hand picking. The efficiency of mechanical harvest was from 85% to 90%. Over 5% of fruits were lost on the ground and from 1 to 5% of fruits were left on the tree. Up to 18% of the plums and no more than 10% of the prunes harvested mechanically showed some damage. They can be fully acceptable for processing, for up to 10 days, providing the potential deterioration processes are inhibited by cold storage. The large-fruited cultivars seem to be more susceptible to bruising than the small-fruited ones. For the latter, the share of marketable quality fruits within the mechanically harvested crop amounted to about 80%, which could be a good prognostic justifying further trials on the prune harvester.