Research on the resistance to frost, susceptibility to sharka, flowering biology, fruit setting, yield, and ploidy levels of 36 Japanese plum cultivars (mostly hybrids of Prunus salicina with Prunus cerasifera) were carried out in 2015–2020 at the Experimental Orchard located in Dąbrowice near Skierniewice. Relatively mild winters with sporadic temperature drops to nearly −21 °C in January of 2017 and 2018 caused slight damage to several cultivars of Japanese plum insufficiently resistant to frost. The trees of most cultivars remained healthy, with no signs of damage. ‘Barkhatnaya’ and ‘Tatyana’ cultivars turned out to be very susceptible to sharka. ‘Herkules’ trees were the most vigorous. ‘Barkhatnaja’, ‘Blue Gigant’, ‘Shater’, and ‘Tatyana’ trees were characterized by weak growth. The trees of Japanese plum started flowering early, usually in the first or second decade of April. Most of the cultivars belonged to early season cultivars, the fruits of which ripened in July. Based on the assessment of tree productivity, ‘Barkhatnaya’, ‘Inese’, ‘Shater’, ‘Tatyana’, and ‘Vanier’ are the best for growing in the climate of Central Europe. ‘Tsernushka’, ‘Chuk’, ‘Dofi Sandra’, ‘Early Golden’, ‘Ewierch Rannyj’, ‘Yevraziya’, ‘Gek’, ‘General’, ‘Kometa’, ‘Kometa Late’, ‘Maschenka’, and ‘Naidyona’ trees also yielded well. ‘Blue Gigant’, ‘Black Amber’, and ‘Herkules’ had the largest fruits, and ‘Chuk’ and ‘Inese’ cultivars produced the smallest fruits. Among the assessed Japanese plum cultivars, those with round fruit, dark skin with various shades of purple, yellow flesh, and A cytometric analysis showed that almost all cultivars are diploid, except for ‘Herkules’ (possibly pentaploid) and ‘Yevraziya’ (possibly hexaploid or aneuploid).

In the field experiment, 8-year-old ‘Sylvia’ and ‘Karina’ sweet cherry trees grafted on ‘GiSelA 3’, ‘GiSelA 5’, ‘Piku 4’and ‘Weiroot 72’ clonal rootstocks were compared with trees of the same cultivars on the standard rootstock F 12/1. The data collected included tree vigour (expressed as trunk cross-sectional area − TCSA), yield, and fruit weight as well as content of soluble solids in fruit. Based on TCSA, the largest ‘Sylvia’ and ‘Karina’ trees were on ‘F12/1’, and the smallest were on ‘GiSelA 3’. The results revealed that all of the tested rootstocks being compared to ‘F 12/1’, significantly reduced the growth of sweet cherry trees. ‘Sylvia’ trees on ‘GiSelA 5’ and ‘Piku 4’ yielded more than those on ‘F12/1’. The highest cumulative yields of ‘Karina’ were harvested from trees on ‘GiSelA 5’. ‘Karina’ trees on ‘GiSelA 3’, ‘Piku 4’ and ‘Weiroot 72’ performed comparably in cumulative yields to those on ‘F12/1’. Rootstock effects on yield efficiency were consistent between the two cultivars, with the most yield efficient trees on ‘GiSelA 3’, ‘GiSelA 5’ and ‘Weiroot 72’, and the least efficient trees on ‘F12/1’. Trees of both cultivars grafted on ‘GiSelA 3’ produced significantly smaller fruits than those grafted on ‘F 12/1’. The rest of the rootstocks, tested in terms of an effect on fruit weight (with the exception of ‘Karina’ on ‘Weiroot 72’), had a similar value to ‘F 12/1’. Effects of rootstock on content of soluble solids in fruit were modest and statistically insignificant.

ISHS V International Cherry Symposium EVALUATION OF NEW ROOTSTOCKS FOR 'VANDA' SWEET CHERRY IN POLISH CLIMATIC CONDITIONS

ISHS IX International Symposium on Plum and Prune Genetics, Breeding and Pomology EVALUATION OF VIGOROUS AND DWARF PLUM ROOTSTOCKS IN THE HIGH DENSITY ORCHARD IN CENTRAL POLAND

A study conducted over three consecutive years examined the effects of using biochar, organic fertilizer and microorganisms on soil pH and the concentrations of macro and microelements in the soil. A tendency to increase soil pH was seen where biochar was used. The highest concentration of phosphorus was found in the soil after the application of organic fertilizer with the addition of microorganisms. The most potassium was found in the soil treated with biochar together with organic fertilizer, while the most magnesium was in the soil fertilized with organic fertilizer alone and organic fertilizer together with microorganisms. All the fertilization combinations resulted in an increase in boron and copper levels in the soil. The accumulation of iron in the soil was promoted by organic fertilization alone and organic fertilization together with microorganisms. The highest amount of manganese in the soil was found after fertilization with biochar together with organic fertilizer. In the combination where organic fertilizer was applied, the soil contained the most sodium, while the highest zinc content was found in the soil fertilized with biochar and organic fertilizer. The greatest increase in the carbon content in the soil occurred after the use of biochar together with microorganisms and biochar with organic fertilizer. The same treatments also resulted in the highest amount of organic matter. The study shows that the use of biochar, organic fertilization and the combined use of biochar and organic fertilization improved the quality of the soil.