Szymajda M., Pruski, K., Żurawicz, E. and Sitarek, M. 2013. Freezing injuries to flower buds and their influence on yield of apricot ( Prunus armeniaca L.) and peach ( Prunus persica L.). Can. J. Plant Sci. 93: 191–198. Each spring, for 3 consecutive years, 2009–2011, the degree of freezing injury to overwintering flower buds of selected cultivars and clones of apricot and peach was evaluated at the Dąbrowice Research Institute of the Horticulture E$xperimental Orchard (District of Skierniewice, Poland). Apricot flower buds were damaged less severely than those of peach during the winter of 2009/2010 when the lowest temperatures (maximum drop in temperature) coincided with the full dormancy stage of the trees. Conversely, peach flower buds were less damaged than buds of apricot when the maximum drop in temperature occurred after the late winter thaw in both 2008/2009 and 2010/2011. Under Polish climatic conditions, peach proved to be more reliable than apricot in consistency to produce fruit. Results have shown that the most hardy apricot and peach cultivars can develop very strong winter hardiness allowing the trees to survive temperatures as low as −28°C, as long as there are no severe temperature fluctuations during late winter.

Szymajda M., Żurawicz E., 2014. Seed genotypes for harvesting seeds in the production of generative rootstocks for peach cultivars. Hort. Sci. (Prague), 41: 160-166.Six novel peach genotypes, designated BN-1, BN-3, BN-4, BN-7, BN-8 and BN-45, were assessed for usefulness as sources of seeds for production of generative rootstocks for peach cultivars. The genotypes BN-8 and BN-1 were the most intensely flowering, while the most abundantly and regularly fruiting genotype was BN-8, which also produced the smallest stones. The smallest fruits and the highest seed yields were produced by the genotypes BN-8 and BN-7. All of the genotypes under assessment produced seeds with higher germination capacities compared with the two control cultivars, Mandżurska and Siberian C, with the seeds of the genotypes BN-8, BN-4 and BN-3 exhibiting the most significantly elevated germination capacities. The most stones with two seeds were produced by the genotypes BN-45 and BN-3; however, produced a smaller fruit crop than did BN-8. Considering the characteristics assessed, the best as a seed source trees was genotype BN-8.

In 2008-2011, at the Research Institute of Horticulture in Skierniewice, Poland seven genotypes of Prunus armeniaca L., designated MN-1, MN-2, MN-4, MN-6, MN-46, MN-53 and MN-59, were evaluated for use as trees to provide seeds for the production of generative rootstocks for apricot cultivars. The study was conducted on trees growing in the Experimental Orchard in Dąbrowice (central Poland). The best as seed trees proved to be genotypes MN-4 and MN-46. Their flower buds are resistant to frost, the flowers are well able to tolerate spring frosts, and the trees yield regularly and produce a lot of small fruit. Trees of these genotypes are also characterized by a relatively low growth vigour and produce seeds with a high germination capacity. The results indicate that genotypes MN-4 and MN-46 are very suitable for harvesting seeds for the production of generative rootstocks for apricot cultivars in countries located in the seasonally cold regions of the temperate climate which represent the northernmost extent of apricot cultivation.

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The possibility of obtaining new varieties of plum resistant to the Plum pox virus by using traditional breeding methods with resistant lines was assessed in [2007][2008][2009][2010][2011][2012]. The source of the resistance was the plum variety 'Jojo' that shows a mechanism of local hypersensitivity, which results in the whole plant being resistant. The assessment covered 435 Prunus domestica seedlings from eleven F 1 hybrid families which had been obtained with traditional breeding methods by crossing the variety 'Jojo' with other plum varieties. The results showed that the variety 'Jojo', used either as a maternal or paternal parent, can be a valuable parental form in plum breeding programmes aimed at obtaining varieties resistant to the sharka disease. Three highly hypersensitive genotypes were obtained: # 4, # 48, and # 186, and an additional 14 were selected for further evaluation. Their production value will be assessed in the coming years.

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Szymajda M., Napiórkowska B., Korbin M., Żurawicz E. (2015): Studies on the interspecific crossing compatibility among three Prunus species and their hybrids. Hort. Sci. (Prague), 42: 70-82.In 2011-2013, a study on the crossing compatibility and the setting of fruit in distant hybridization within the genus Prunus, among the species P. armeniaca L. (apricot), P. salicina Lindl. (Japanese plum), P. cerasifera Ehrh. (myrobalan plum) and the hybrids P. salicina × P. cerasifera was conducted at the Institute of Horticulture in Skierniewice, Poland. The percentage of fruit set depended on the direction of pollination of the crossed species. Most fruits were obtained by crossing P. salicina × P. armeniaca and P. salicina × P. cerasifera. The largest number of fruitlets in relation to the number of pollinated flowers was obtained when two genotypes of P. salicina -Czernuszka and D 17-73, were the maternal parents. The results show that the crossing compatibility and effectiveness in the cross-breeding of the studied species of Prunus are influenced to a greater extent by the genotype of the maternal form of P. salicina than by the genotype of the paternal form of P. armeniaca and P. cerasifera.