The sunflower ( Helianthus annuus L.) is a fundamental oil-yielding culture for Bulgaria and the world and thus special attention is paid to it. Various selection methods have been used over the years and as a result of successful breeding programs new sunflower forms lines ( В / А and R ) and hybrids (oil and confectionery type) were created in Bulgaria. Some of these new forms have new plant architectonic different vegetation periods seeds with different sizes and coloration high combining ability resistance to diseases the parasite Broomrape and some herbicides high seed oil and fatty acid content genes for restoration of fertility ( Rf genes) and different types of cytoplasmic male sterility ( CMS ).

Cultivated sunflower ( Helianthus annuus ) is not typically considered to have a pleasant floral fragrance. In field production seed yield is often limited by pollination services particularly in the production of hybrid seed. Improved floral fragrance as determined by volatile organic compounds may be a route to improving pollinator attraction for oilseed and confectionary production and could also add value to ornamental sunflowers. Wild relatives of H . annuus have a long history of being used to breed improved traits into cultivated varieties yet it is unknown whether favorable scents are present in wild Helianthus species and thus an available resource for fragrance breeding. In order to assess the diversity of floral fragrance available in crop wild relatives 30 diverse accessions of wild Helianthus as well as seven varieties of H. annuus spanning a domestication gradient were grown in greenhouse experiments and variation in floral volatiles was analyzed by solid phase microextraction-gas chromatography-mass spectrometry. While alpha-pinene made up a significant portion of the volatiles emitted for most taxa there was substantial diversity present across the genus as well as within H. annuus . Most volatiles emitted were monoterpenoids with a significant share of sesquiterpenoids. The diversity identified here will inform further targeted study of which compounds affect pollinator attraction and health. Several wild accessions such as Helianthus debilis subsp. tardiflorus and Helianthus praecox subsp. praecox as well as open-pollinated domesticated accessions of H. annuus show promise for breeding for improved floral fragrance due to high volatile abundance and likely favorable compound compositions.

The present study was focused on the assessment of genetic diversity in twenty-three populations of Orobanche cumana parasitizing on sunflower in Bulgaria Turkey Moldova and Romania using 13 ISSR markers. The obtained results on the genetic diversity parameters showed that the broomrape populations were characterised by a significant level of the intrapopulation diversity. In addition descriptive population genetic statistics revealed that Turkish populations had a higher level of genetic diversity indices than populations from several areas of the northeast and east of the Balkan Peninsula included in Eastern Europe. The analysis of molecular variance showed that 38 % of the genetic variability was due to differences within populations 34 % was due to differences among populations and the lowest molecular variation was among countries (28 %). According to clustering and PCA methods Moldavian Bulgarian and Romanian broomrapes shared more genetic traits with each other than with Turkish populations within a main gene pool. As a whole all results of this study showed that there is a high intrapopulation diversity of the O. cumana gene pool in the Black Sea basin. From the clustering and PCA analyses it can be concluded that the grouping of broomrape populations is partly determined by their geographical origin as well as by the genetic differences and similarities accumulated over time and is not related to virulence. The information obtained from this study may be highly relevant in contributing to the development of sustainable control strategies of the pathogen and breeding programmes for sunflower resistance to broomrape.

The impact of biotic (infestation with the Orobanche cumana ) and abiotic stress (drought) factors on the productivity indicators of sunflower hybrids was evaluated in two years 2020 and 2021 which were significantly different regarding to the weather conditions. The Principal Component Analysis (PCA) was applied on 10 parameters: plant height (PH); leaf number (LN); leaf area (LA); seed yield (SY); leaf area index (LAI); chlorophyll a content (Chla); chlorophyll b content (Chlb); carotenoids content (Car); chlorophyll pigment ratio (Chla/b); total of chlorophyll pigments (Chla+b) that are directly or indirectly associated with the productivity of sunflower hybrids. The first two PCs explained 75 % (drought stress for 2020) and 83 % respectively (stress caused by broomrape infestation) of the total variance of parameters or hybrids. A higher number of positive correlations were identified between the studied morpho-physiological indices differentiating the hybrids. The SY index correlated with PH LN LAI LA ( r = 0.54–0.78) under biotic and abiotic stress. Also seed yield related with the content of pigments ( r = 0.65–0.79) in the case of infested hybrids with broomrape. The infested hybrid H11 in both years showed the highest values for most of the analyzed indices indicating a relatively high degree of tolerance to the combined stressors.

It is proposed to study the qualities of sunflower seeds in three zones of location in the head. Moderate negative correlations of the sign of the number of lateral heads (branching) in sunflower lines from the mass of 1000 seeds the number of rows seeds in a row the total number of seeds and the diameter of the head were established ( r = −0.5 to −0.53 * on the Chedokk scale). The dependence of the number of seeds in the head on its size was confirmed ( r = 0.83). In particular we obtained a high positive correlation between the signs of the number of rows in the head and the number of seeds in the row with the size of the head (0.71 and 0.72). It was established that the mass of 1000 seeds of the first tier has correlations with the number of seeds in a row and the number of rows ( r = 0.32 and 0.39) which are attributed only to the group of noticeable ones. This indicates the possibility of combining in one plant a large number and size of seeds in the head. It was found that changes in the size and weight of the seeds in the head by zone occur in hybrids and lines gradually while the variety shows only a slight decrease in the size and weight of the seeds in the third zone. The largest quantity and the best confectionary quality of seeds was provided by the Zaporizhzhya Confectionery variety. In hybrids the output of seeds weighing 90–80 g from one head reached only 1000 pieces. The potential to increase the number of seeds in heads in hybrids is present but the size of the seeds is critical. With the available average weight of 1000 seeds: 90 g in the best maternal line and 70 in the best paternal line the hybrids only approached the 100 g mark.

The presented results of the study on the effect of biopreparations and different fertilizer systems on the formation of sunflower yield and productivity determination of economic efficiency of sunflower cultivation under sharp fluctuations in climatic conditions through the use of biotechnology elements and fertilization. Growing sunflower without seed treatment with biopreparations under mineral fertilizer system provided an average yield of 2.93 t/ha with an additional 0.31 t/ha of sunflower seeds. The organo-mineral fertilizer system resulted in the highest increase in additional production – 0.50 t/ha and the increase in sunflower yield through fertilization system was the most significant with a minimum important difference (MID 05 ) of 0.11 t/ha. Seed treatment with biopreparation contributed to an increase in sunflower yield in all fertilizer systems: without fertilizer application only due to the action of biopreparation the yield increased to 2.82 t/ha; application of mineral fertilizer ensured a harvest of 3.09 t/ha of sunflower seeds; the organo-mineral fertilizer system had the highest yield indicator – 3.23 t/ha. The highest output of dry matter from the production was obtained through seed treatment with biopreparation and the use of organo-mineral fertilizer system which provided a yield per hectare of: grain units – 6.47 t fodder units – 3.56 t digestible protein – 1.23 t. However the most significant increase in sunflower productivity was observed in the organo-mineral fertilizer system without seed treatment with biopreparation. The highest indicators of economic efficiency of sunflower cultivation were observed under the conditions of seed treatment with biopreparation without fertilizer application which amounted to 18322 UAH/ha – net profit at a profitability of 91.5 %.

Areas of sunflower cultivation in Ukraine Europe and the world have significantly increased over the past decade along with an increase in crop yield largely due to the development of new varieties and hybrids resistant to various abiotic stresses and extreme environmental conditions. The mineral nutrition background is also an important element of sunflower cultivation technology. The influence of mineral fertilizer rates on the productivity of new early-maturing and medium-early sunflower hybrids was the focus of research conducted during 2020–2021 on dark chestnut soils in the southern region of Ukraine. The results of the study showed that optimization of the mineral nutrition background contributed to increased plant height and leaf area. Both indicators were maximized for the cultivation of Alambra KS and Blyutuz hybrids with the application of fertilizers at the rate of N 90 P 60 . These experimental variants also ensured the formation of the maximum level of seed yield (3.05 t/ha for Alambra KS hybrid; 3.39 t/ha for Blyutuz hybrid) and the highest indicators of profitability per 1 kg of active substance of fertilizers (0.35 tons for Alambra KS hybrid; 0.45 tons for Blyutuz hybrid). The mineral nutrition background had little effect on the oil content in sunflower seeds. With an increase in the nitrogen fertilizer rate on the phosphorus background the oil content in the seeds slightly decreased. However the experimental variants differed in terms of conditional oil output per hectare of sunflower cultivation. Among early-maturing hybrids the Alambra KS hybrid showed a higher value for this indicator while among medium-early hybrids it was the Blyutuz hybrid. The most effective rate of mineral fertilizers in terms of oil output was determined to be N 90 P 60 . Based on the results of the study on dark chestnut soils in the southern region of Ukraine it is recommended to cultivate the Alambra KS hybrid among early-maturing sunflower hybrids and the Blyutuz hybrid among medium-early hybrids with the application of mineral fertilizers at the rate of N 90 P 60 .