The present study was conducted during the period 2020–2023 under the agroecological conditions of the Troyan plum-growing region, with the aim of assessing the susceptibility of plum cultivar–rootstock combinations to three economically important fungal diseases: rust (Tranzschelia pruni-spinosae), shot hole disease (Stigmina carpophila), and red leaf spot (Polystigma rubrum). Four widely grown plum cultivars (Сacanska Lepotica, Hanita, Jojo, and Stanley), grafted onto six rootstocks (Brompton, GF 655-2, SJ A, Wavit, Wangenheim, and Prunus cerasifera), were evaluated under natural infection conditions. Climatic parameters were recorded annually to determine their influence on pathogen development. Significant differences in disease severity were observed among cultivars and rootstocks. The highest incidence of shot hole disease was recorded in the Hanita/Wavit combination (44.66% in 2022), while the cultivar Stanley showed pronounced susceptibility to rust when grafted on Brompton and Wavit rootstocks (31-37%). In contrast, combinations Cacanska Lepotica involving GF 655-2 and Wavit rootstocks exhibited the lowest overall disease susceptibility. These results highlight the critical role of rootstock selection in reducing disease pressure and improving the resilience and sustainability of plum orchards under changing climatic conditions. Highlights This study presents a comprehensive multi-year evaluation of the response of plum cultivar–rootstock combinations to major fungal diseases under variable climatic conditions. Rootstock selection significantly influenced disease severity and yield stability across all studied cultivars. Integration of long-term climatic data with disease assessments provides new insights for climate-resilient plum production.

In the period from 2020 to 2022, the biological and pomological characteristics of the early ripening plum varieties 'Ruth Gerstetter', 'Tuleu Timpuriu', 'Katinka', 'Tegera', 'Hanita', 'Cacaks Early', 'Cacaks Beauty', 'Green Renclode' and 'Top First (R) were investigated in the experimental plantations of the Research Institute of Mountain Livestock Breeding and Agriculture Trojan (RIMSA)-Trojan. The parameters analyzed included the flowering phenophases, ripeni ng time, pomometric and physicochemical characteristics of the fruit, and yield of the trees, in each case in comparison with the standard variety,Cacaks Beauty'. In the period studied, the earliest flowering was observed in ,Tuleu Timpuriu' (April 7-12), while ,Ruth Gerstetter' had the longest flowering period (15 days). The shortest flowering phase (12 days) was observed in ,Cacaks Early', which also bore the largest fruit (55.30 g). Early ripening plum varieties grown in the Trojan region have a lower dry matter value compared to the standard. The highest values of total polyphenols were found in ,Katinka' (376.83 mg/g), followed by ,Tule Timpuriu' (303.22 mg/g). The highest yield was observed in the standard variety (44 kg/tree), followed by ,Cacaks Early' and ,Katinka' (31-32 kg/tree). Varieties ,Green Renclode', ,Hanita' and ,Tegera' are not only suitable for fresh consumption but also show potential for processing into juices, nectars and distillates.

The cultivars from the Top series of the breeding program Dr. Jacob, Geisenheim, Deutschland are now widespread in almost all European countries. They are of interest for modern, sustainable plum production. The data we present are from the Troyan region, an experimental field of the RIMSA. The plantation was established in 2008, with the varieties of the fruits, as well as the color parameters of the fruit skin and fruit flesh in 2021 and 2024 were studied. It has been established that the mid-ripening varieties Topgigant Plus, Topfive, Tophit have larger fruits (40-50 g). Late-ripening varieties are characterized by a very high content of dry matter and total sugars and a low content of organic acids. This makes them extremely suitable for processing, given the small mass of the fruit (Topking, Topper). The color of the fruit skin in all varieties is dark blue, with shades of purple and dark purple. The fruit flesh is yellow, juicy, sweet.

For the period 2019-2022, the phenological manifestations were studied of the Serbian plum cultivars such as 'Cacanska rana', 'Cacanska najbolja', 'Cacanska lepotica', 'Cacanska rodna', and 'Valjevka' and their response to climatic factors such as temperature, rainfall, relative air humidity in RIMSA-Troyan. The trees are grown on light gray forest soil, under non-irrigated conditions, with tillage between the inter-row spacing. The phenophases were studied, such as the beginning of flowering, end of flowering, and fruit ripening periods. The earliest flowering began in 2019 for 'Cacanska rodna' cultivar (28.03.), and the latest flowering began on 6.04.2019 for 'Kyustendilska plum'. In the following years, spring temperatures delayed the vegetation onset and the beginning of flowering was around 07.04 for 'Cacanska lepotica', followed by 'Cacanska rodna' (10.04.) and 'Cacanska najbolja' (12.04). The latest end of flowering was reported on 7-8 May 2022 ('Valjevka' and 'Kyustendilska plum'). For the entire study period, the phase from flowering to harvest maturity was shortened. To obtain favorable conditions for growth and fruit-bearing in the Central Balkan Mountain region, the introduced Serbian cultivars require changes in cultivation technology and adaptation to changes in the global climate.

Background. The biological and economic qualities (including morphological, biochemical and sensory properties) of Serbian plum cultivars are of interest for fruit production in the European Union countries. Studying their agro-biological and pomological properties can assist farmers in making informed choices. The research aims to characterise the Serbian plum cultivars '& Ccaron;a & ccaron;anska Rana', '& Ccaron;a & ccaron;anska Lepotica', '& Ccaron;a & ccaron;anska Najbolja', '& Ccaron;a & ccaron;anska Rodna' and 'Valjevka', as well as the local cultivar 'Kyustendilska'. 'Stanley' was included as a control, and the study focuses on both biological and economic qualities under the agro-ecological conditions of the Troyan Mountain region. Material and methods. The study was conducted in an experimental plantation of the Research Institute of Mountain Stockbreeding and Agriculture (RIMSA), Troyan (42 degrees 53 ' N 24 degrees 43 ' E, altitude 420 m) from 2020 to 2022. Reproductive, biochemical and colour parameters were analysed. Results. The study established that the cultivars '& Ccaron;a & ccaron;anska Rana' and '& Ccaron;a & ccaron;anska Najbolja' produced the largest fruits, weighing 46-48 g, with relatively large stones, comprising 4-4.5% of the fruit's weight. The fruit skin of all cultivars was characterised by a dark blue colour with shades of purple, blue, and dark blue. Among the cultivars, the 'Stanley' had the hardest skin, while '& Ccaron;a & ccaron;anska Najbolja' had the softest. Similarly, the fruit flesh was the firmest in 'Stanley' and '& Ccaron;a & ccaron;anska Lepotica'. Yields depended entirely on changes in climatic conditions by year. The cultivar '& Ccaron;a & ccaron;anska Rodna' is noted for its high content of soluble solids, polyphenols and anthocyanins, as well as a relatively high sugar content and a low acidity. These attributes make it suitable both for fresh consumption and processing. The cultivar '& Ccaron;a & ccaron;anska Najbolja' is characterised by high sugar and acid content along with very low levels of soluble solids. Its taste is described as wellbalanced and very pleasant. Conclusion. All studied cultivars are well-suited for cultivation under the conditions of the Troyan Mountain region. They produce large, flavourful fruits with a rich biochemical composition and are highly recom

A comparative study was done on the biological and economic characteristics of plum varieties of Prunus domestica L. grown under agroecological conditions of Lovech (RIMSA - Troyan) and Gabrovo regions (the Plum Experimental Station Dryanovo). The observations were conducted in the period 2019 - 2021 of the varieties such as 'Cacanska lepotica', 'Cacanska najbolja', 'Cacanska rodna', 'Gabrovska', 'Strinava' and 'Stanley', selected for the control. The phenological phases of flowering and harvest maturity of the fruits were determined. Biometric measurements and the chemical composition of fresh plum fruits were made. It was found that the fruits of the large-size varieties such as 'Cacanska lepotica' and 'Cacanska najbolja' had an average weight (41 - 48 g) for the Troyan region, and 42 - 45 g for the region of Dryanovo, which are suitable for fresh consumption. The fruits of the 'Cacanska rodna', 'Strinava', and 'Gabrovska' contain over 20% dry matter in both regions, which makes them suitable for drying and distillation. The studied plum varieties are suitable for growing in the study areas and may be recommended for the expansion of the variety assortment in the establishment of new plum plantations for fresh consumption and processing.

The purpose of this paper was to analyze the influence of climatic factors and their impact on the phenology of some plum varieties grown in RIMSA Troyan during the period 2019-2021. The phenophases of the beginning of flowering, the end of flowering and the period of fruit ripening were observed and analyzed. Regarding the flowering phenophase, it was found that earliest blossoming of plum cultivars occurred at the beginning of April in 2019. The blossoming period for 'Kyustendilska' both began and ended at the latest time. Every year, within 10-11 days, there was a complete overlap of the blossoming of all the studied cultivars. Regarding the fruit ripening, higher temperatures combined with low amounts of precipitation, cause an earlier onset of the ripening phase.

The study was conducted in the towns of Troyan and Apriltsi and the nearby villages and hamlets in the Central Balkan Mountain. During the expedition research, heirloom local apple cultivars and forms threatened with extinction were discovered, marked and described. Their reproductive characteristics were studied. A large genotypic diversity of the genus Malus, L. have been observed. The complex of agroecological conditions favours the growth, and longevity of the apple trees. Most discovered and described trees are more than 100 years old, more than 15 m tall and more. The trees bear fruit abundantly, but there is a tendency to alternate their fruit bearing. The subject of the present study are 11 late-ripening valuable cultivars with large-size fruit threatened with extinction, such as 'Kandile' -129.51 g, 'Sadova Perusha' -108.07 g, etc., with the aim of studying their morphological, pomological and reproductive characteristics. It has been found that most of them are distinguished by an attractive appearance, intensely coloured fruit skin and valuable nutritional and dietary qualities. Their long-term storage under home conditions is also a valuable quality.

The main phenological and biological features of the introduced apple cultivars were studied, for the period 2019-2021 in the region of Troyan. In order to establish their influence on the phenological manifestations of apple cultivars in order to be able to recommend them for cultivation from a practical point of view. It was found that in 2021 flowering was abundant and occurred 5-8 days later than the previous year. The latest date for the end of flowering was registered for the "Reanda" cultivar on May 12. The period from the beginning of flowering to its end is about 15-17 days. The fruits of the observed apple cultivars ripened in the period from mid-September to the first 10 days of October. The fruits of 'Remo' and 'Revena' reached the earliest stage of ripening, and 'Granny Smith' was the latest.

Japanese quince (Chaenomeles sp. Lindl.) is fruit-medicine plant that is getting attention in the last year in Bulgaria. It has valuable nutritional, dietary and medicinal qualities and deserves to be introduced into culture in Bulgaria. The experiment was conducted in the three-year period (2018-2020) in the collection of RIMSA Troyan, Bulgaria. The reproductive characteristics of the perspective for fruit production genotypes were studied with an average yield higher than 3.5 kg per plant. They were followed also by fruit weight and biochemical compounds. During the period of the study genotype SCH4 was with the highest average yield (6.88 kg), followed by SCH3 (5.09 kg). The thornless genotype SCH 6 is with the lowest yield (3.71 kg).

During research expeditions in the Central Balkan Mountain region, trees of late-ripening (mid-October), rare local cultivars, and forms of apples with valuable pomological and biological qualities were marked. In 2021, all marked forms bore abundant fruit. The highest yield (280 kg per tree) was registered in `Meka Shekerka' cultivar (MS F1). The fruit weight was on average 59.50 g, obloid form, low percentage of dry matter (12%), a high percentage of total sugars (18%), and the highest glucoacidimetric coefficient. BF1 was distinguished by yields of 140-150 kg per tree, very good taste of the fruit (lowest acid content 0.27%), attractive appearance (green-yellow with a blush on the sunlit side), white fruit flesh, pleasant taste with a pronounced aroma of green apple, abundant waxy coating, with a mass of 86.17g and globose fruit shape. Our scientific data are compared with the information obtained from the local population on age, origin, fruitfulness, use, and distribution in the region.

The study was conducted in the period 2018-2020 on the territory of RIMSA Troyan with three cherry cultivars, such as `Oblachinska', `Karneol' and `M 15', grafted on `Alkavo' rootstock and planted in 2002 by trench method with local, stockpile organic fertilizing. The planting scheme was 4 x 3 m and they were grown under nonirrigated conditions. The reaction of the sour cherry cultivars, the intensity of the infestation and the manifestation of cylindrosporiosis and shot hole disease for the optimization of the schemes for sustainable Plant Protection under the climatic conditions of the Troyan region were studied. `Karneol' was found to have the lowest susceptibility to both diseases studied (shot hole disease <8.7%; white rust 21.3%). The average fruit weight was 5.5 g, it is suitable for fresh consumption, with an extremely balanced taste and with opportunities for organic and sustainable cultivation, and the later ripening period allows to extend the harvesting period. `M15' had a higher infestation index of Stigmina carpophila (Lev.) Ell (15.3%) compared to the other two cultivars and was more susceptible. Infestation index of Blumeriella jaapii (Rehm.) was slightly higher, but was well below 50%. It has attractive fruits with greater weight, bears abundant fruit and can be included in the cultivar list of modern sustainable technologies.

The study was conducted in RIMSA-Troyan in the period 2014-2018, in a plum plantation of `Katinka' cultivar, under non-irrigated conditions, on pseudo-podzolic gray forest soils, poorly stocked with nutrients. The impact of different soil surface management systems (fallow, natural grassland, artificial grassland) on vegetative and reproductive indicators of plum trees was observed. Data showed that the largest growth of the trunks was registered in soil managed as an artificial grassland (trunk section 2014-30.01cm(2); 2015-39.01cm(2); 2017-60.56cm(2); 2018-70.92cm(2)) and the highest annual growth was observed for each year of the study period, formed by higher number of annual twigs. In the formation of the volume and projection of the crowns, no patterns have been established regarding the soil management way. The highest yields were reported in 2017 with 14 kg/tree and in 2018 with 9.1 kg/tree from an artificial turf as a soil management system, which had a positive effect on other reproductive indicators, such as weight and size of fruit.

The study was conducted in the period 2017-2019 in an intensive plum plantation of the RIMSA Troyan. The susceptibility of the rootstock combinations to Polistigma rubrum (Persoon) De Candolle, Tranzschelia pruni spinose (Persoon) Dietel, Stigmina carpophila (Lev Ellis) was studied. The infectious process of infection and development was monitored and the degree of attack of Polistigma rubrum (Persoon) De Candolle, Tranzschelia pruni spinose (Persoon) Dietel, Stigmina carpophila (Lev Ellis), in plum rootstock combinations for the climatic conditions of the region of Troyan were reported. The climatic factors - temperature and precipitation during the infection and manifestation of the diseases have a significant influence on the degree of damage. Studies have found that in all treatments of the study, the highest values for the degree of attack of Polistigma rubrum (Persoon) De Candolle, Tranzschelia pruni spinose (Persoon) Dietel, Stigmina carpophila (Lev Ellis) were reported for 2019, due to the fact that the year is characterized by heavy and prolonged rainy periods, especially the month of June (234.6mm). During the 3 years of the study, the rootstock combinations with Wavit were characterized by a high attack index for the three diseases Polistigma rubrum (Persoon) De Candolle, Tranzschelia pruni spinose (Persoon) Dietel, Stigmina carpophila (Lev Ellis). Stigmina carpophila occurs exclusively in the treatments with Brompton for the cultivars 'Hanita' and 'Stanley' and in the rootstock Wavit in 'Cacanska Lepotica' and 'Jojo'. The lowest degree of attack has the cultivar 'Hanita' (average 23%), and the highest is in 'Cacanska Lepotica' on Wavit (46.4%).

The chemical composition of fresh plum fruits of 'Katinka' cultivar was studied for a 5-year period (2015-2020) in an experimental plum plantation of RIMSA Troyan. The soil surface in the plantation is maintained in three treatments black fallow, natural grassland and artificial grassland. It was found that the content of dry matter and acids in the fruits of 'Katinka' were not affected by the way the soil surface was managed. These indicators varied relatively little over the years, in the range of less than 1.5% for dry matter and from 0.41% to 0.82% for acids. There was a higher percentage of total sugars in fruits in the artificial grassland for all years of the study period and varied from 9.05% to 11.60%. The most favourable values for the ratio between sugar and acids in fruits (glucoacidimetric coefficient) were reported in the artificial grassland, which is important for the formation of good taste qualities of the fruits with variation over the years from 13.89-27.07. In the case of fallow and natural grassland treatments, a high correlation dependence was established between the content of organic acids and inverted sugar.

The study was conducted in the period 2019-2020 in plum plantations of RIMSA Troyan. The pomological and physicochemical parameters of widespread and newly studied plum cultivars with different directions of use were studied. It was found that cv. 'Strinava', 'Stanley', 'Jojo' and 'Elena' have a dry matter of over 19%, and in 'Stanley' and 'Jojo' the total sugars are also at most 11.5-12.5%. 'Hanita' cv has the highest content of titratable acidity (1.0%), all others are <1.00%. The large-fruited cultivars with an early ripening period 'C. Naibolya', 'C. Lepotitsa', 'Tuleu timpuriu', as well as the later ripening 'Jojo' have a well-balanced taste, glucoacidimetric coefficient of about 20, which makes them suitable for fresh consumption. 'Kyustendilska', 'Elena', 'Gabrovska', 'Valevka' cultivars have low fruit weight, the late ripening period allows them to accumulate a high content of dry matter, which makes them suitable for industrial processing and distillation.

Due to the need to expand its plum assortment in the mountainous regions of the country, the German plum cultivars from the selection program of Prof. Jacob's collection at the Geisenheim Research Station in Germany, 'Topgigant plus'. 'Topking', 'Topper', 'Top 2000'. 'Top', 'Topend plus'. 'p33-6-94'. were introduced in the RIMS4 Troyan in 2008. For the period 2016-2019, the climatic factors of the Troyan region were analyzed the phenology of the cultivars (flowering and ripening time), vegetative and reproductive characteristics were supplemented which were complemented by laboratory analyzes of the fruits. The 'Top 2000' cv. was first blossomed (at the end of March, the first days of April, depending on climatic conditions. The lowest growth was in the 'Topper' cv., which was adapted to intensify the planting scheme. The largest are the fruits of 'Topgiant plus' (77.34 g) and have the smallest share of stone (2.75%) for 2019, ripening relatively earlier than the others. The highest content of total sugars (9.4%) and high glucoacidimetric ratio (12.37) are of the 'Topper' cv.. 'Topper' (0.18 kg / cm(2)) and 'p33-6-94' (0.15 kg / cm(2)) are distinguished by high productivity values. The German plum varieties of the Top group are suitable for cultivation in the mountainous conditions of the Troyan region, using technologies that meet the specificities of each cultivar.

Grey forest soils with heavy sandy clay structure and low nutrient availability are characteristic for the conditions of the region of Troyan. Climate conditions are the following: the average annual temperature is about 10°С and the annual rainfall is about 750 mm. The duration of vegetation period is 245 days. The experiment includes small-sized plum cultivars 'Tegera' and 'Elena', grafted on Mirobolan seedlings, and planted in 2000; and 'Katinka' grafted on 'Fereley' rootstock, planted in 2005, all are being grown under non-irrigated conditions. The aim is to determine the influence of soil and climate factors in the region of Troyan over the phenology and reproduction of the introduced German plum cultivars of 'Katinka', 'Tegera' and 'Elena'. The flowering, some vegetative and reproductive indicators were observed and chemical analysis of fruits was conducted for characterization of their taste qualities. It is found that in the foothill region of Troyan, plum cultivars find favourable conditions for growth and development, but they require regular agrotechnical measures and increased attention in extreme climate changes. In 2015, which was a favourable year, the plum harvest of 'Katinka' was about 40 kg per tree. Fruits had very small weight (15; 16; 21g), but the great quantity gave opportunity for high yield. The earlier ripening cultivars 'Tegera' and 'Katinka' accumulate less dry matter in comparison with the late ripening cultivar 'Elena'.