Surface sterilization is the most important step in preparation of explants for micropropagation, because controlling fungal and bacterial contamination of woody plant from field sources is very difficult. Six sterilizing agents: sodium hypochlorite (NaOCl), calcium hypochlorite [Ca(ClO) 2 ], sodium dichloroisocyanurate (DICA), mercuric (II) chloride (HgCl 2), silver nitrate (AgNO 3) and hydrogen peroxide (H 2 O 2) were tested for sterilization of 'Oblačinska' sour cherry buds, by varying their concentration and time of exposure. The aim of this study was to establish best surface sterilization for in vitro propagation of 'Oblačinska' sour cherry. Aseptic cultures of 'Oblačinska' sour cherry were established from axillary buds which were placed in nutrient medium, supplemented with plants hormones 6-benzylaminopurine (BA), 1naphthaleneacetic acid (NAA) and gibberellic acid (GA 3). The results indicated that among these sterilizing agents silver nitrate (AgNO 3) at concentration of 1% for 20 minutes was the best for controlling the infection, whereas sterilization with sodium dichloroisocyanurate (DICA) at concentration of 1% for 10 minutes was not satisfactory.

Fruit skin colour plays a major role in quality assessment of food, significantly determining consumer`s choice. Colour of sour cherries depends on anthocyanins which are phenolic compounds (flavonoids) present in high amounts in fruits. The aim of this study was to determine a possible relation between polyphenols (total phenolics and anthocyanins) and colour parameters of fruit skin of sour cherries. The plant material used in this study was twenty two sour cherry genotypes from an orchard of Agricultural Institute Osijek. Total phenolics and anthocyanins contents as well as colour parameters (L*, a*, b*, h and C) of fruit skin were determined. Variability between sour cherry genotypes in total phenolics and anthocyanins as well as in colour parameters was revealed. Total polyphenols content varied from 462.7 to 1049.0 mg GAE/100 g of fresh weight, while total anthocyanins ranged from 160.1 to 495.6 mg CGE/100 g of fresh weight. A significant positive correlation was found between polyphenols and anthocyanins content. Total phenolics content had a significant negative correlation with colour parameters b* and h, while anthocyanins content negatively correlated with colour parameters L*, b* and h. According to the obtained results, genotypes Maraska, Heimanns Konservenweichsel and Rexelle are the richest genotypes in polyphenols and anthocyanins content

-Drought is a limiting factor in fruit production today. Identification of sour cherry genotypes tolerant to drought will enable the sustainability of fruit production. The aim of our study was to select sour cherry genotypes according to their genetic background as well as drought tolerance and investigate possible mechanisms of drought tolerance through the changes in photosynthetic apparatus (i.e. photosynthetic pigment content) and photosynthesis process assessed through the chlorophyll fluorescence transient. All of them together with molecular markers (SSRs and AFLPs), relative water content (RWC) as indicator of plant water status distinguish two genotypes (Kelleris 16 and OS), which are the opposite in regards to drought tolerance. Down-regulation of photosynthesis in drought-treated Kelleris 16 plants was seen as changes in antenna complexes of PSII (decreased total chlorophylls content (a+b) and chlorophylls ratio (a/b)). Despite unchanged maximum quantum yield of PSII in drought-treated leaves of genotype OS, overall photosynthetic performance expressed as PI ABS was down-regulated in both investigated genotypes. However, decrement of PI ABS was much pronounced in genotype Kelleris 16, mainly because of changes in a certain fraction of RCs, which become dissipative centres, seen as increase in ABS/RC and DI 0 /RC, in order to avoid photooxidative damage of photosynthetic apparatus. Also, electron transport, seen as decrease in ET 0 /(TR 0 -ET 0 ) and ET 0 /RC, was impaired which lead to impaired CO 2 fixation and photosynthesis. The described changes in the functioning of photosynthetic apparatus in drought-treated plants of Kelleris 16 constitute the main distinction between the two investigated genotypes regarding drought adaptation mechanisms.

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The photosynthetic apparatus rapidly responds to the environmental influences. In vivo chlorophyll fluorescence was applied for the evaluation of photosystem II (PSII) and electron-transport chain functioning and for determination of photochemical and nonphotochemical quenching in chlorotic spruce needles exposed to urban pollution. More injured needles had lower content of chloroplast pigments and changed chloroplast ultrastructure, in comparison with less injured needles. The maximum PSII efficiency was measured in darkadapted samples, whereas other parameters were measured under low and high light conditions (125 and 1400 µ mol photons/(m 2 s), respectively). The PSII efficiency and relative electron transport rate (rel. ETR) were lowered at both irradiance levels while the photochemical quenching was significantly lower only in high light. Nonphotochemical quenching coefficients ( qN ) values were higher at both light levels in more injured needles, however, the difference was insignificant. High nonphotochemical quenching in both needle groups probably made possible the photosynthetic apparatus to function at the high light level. Our results suggested that the lowering of the chlorophyll content could be considered as a protecting event rather than just the consequence of the stress.

The goal of this investigation was to determine genetic differences between autochthonous and introduced cultivars of sweet cherry and between cultivars and types of sour cherry, and to find and optimize a method for the rapid recovery of clonal material. A great number of cherry cultivars and types within the population of cv. Oblačinska sour cherry exist in Croatia and the selection of autochthonous cultivars based on special visible properties for further investigation has been done in previous research. Differences were found in a number of important agronomic traits within the populations of cv. Oblacinska sour cherry. It is suspected that autochthonous sweet cherry cultivars are synonyms for known old cultivars, which were introduced randomly and naturalized under local names. In this approach difficulties arise from the effect of non-genetic factors on the expression of certain traits. The genetic/physiological problem of S allele autoincompatibility exists within sweet cherry cultivars. The detection of S alleles is required to determine compatible cultivar pairs in the orchard. Biotechnological methods based on the polymerase chain reaction (PCR) facilitate faster virus detection compared with classical serological methods and indexing. Thermotherapy and tissue culture make it possible to recover valuable clone material for introduction in the premultiplication process.