Genotype-dependent responses of apples to drought stress were evaluated between commercial and traditional apple cultivars. The results indicate different mechanisms of tolerance to investigated drought stress conditions. Chlorophyll fluorescence induction (OJIP) parameters, chlorophyll and carotenoid content, malondialdehyde (MDA), hydrogen peroxide (H₂O₂), proline, phenols and leaf water content (WC) were measured. The traditional cultivar “Crvenka” confirmed the best tolerance to a drought stress condition, presenting higher photosynthetic efficiency, higher leaf water content, higher levels of chlorophyll content and lower lipid peroxidation with greater membrane stability. The commercial cultivar “Golden Delicious Reinders” showed decreased water content in leaves, increased lipid peroxidation levels and photoinhibition. Considering all results, the commercial cultivar “Golden Delicious Reinders” was adversely affected by drought, while traditional cultivars exhibited better tolerance to drought stress.

The aim of this study was to evaluate physiological responses to short-term heat stress in the leaves of traditional (Bistrica) and modern (Toptaste) plum cultivars. In this study, detached plum leaves were incubated at 25 °C (control) and 40 °C (stress). After 1 h of exposure to heat (40 °C), chlorophyll a fluorescence transients were measured, and several biochemical parameters were analyzed. Elevated temperature caused heat stress in both plum cultivars, seen as a decrease in water content (WT), but in the leaves of the cultivar Bistrica, an accumulation of proline and phenols, as well as an accumulation of photosynthetic pigments, suggest the activation of a significant response to unfavorable conditions. Conversely, in the leaves of Toptaste, a significant accumulation of malondialdehyde (MDA) and an activation of guaiacol peroxidase (GPOD), all together with a decreased soluble proteins content, indicate an inadequate response to maintaining homeostasis in the leaf metabolism. The impact of an elevated temperature on photosynthesis was significant in both plum cultivars as reflected in the decrease in performance indexes (PI_ABS and PI_total) and the maximum quantum yield of PSII (F_v/F_m), with significantly pronounced changes found in Toptaste. Unlike the traditional plum cultivar, Bistrica, in the modern cultivar, Toptaste, short-term heat stress increased the minimal fluorescence (F₀) and absorption (ABS/RC), as well as Chl b in total chlorophylls. Additionally, the inactivation of RCs (RC/ABS) suggests that excitation energy was not trapped efficiently in the electron chain transport, which resulted in stronger dissipation (DI₀/RC) and the formation of ROSs. Considering all presented results, it can be presumed that the traditional cultivar Bistrica has better tolerance to heat stress than the modern cultivar Toptaste. The cultivar, Bistrica, can be used as a basis in further plum breeding programs, as a source of tolerance for high temperature stress.

High temperatures have significant impacts on fruit tree production. Foliar spraying application of promoting agents can be a sustainable approach to managing high-temperature stress in orchards. The mechanism of certain improving agents on ph...

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.

Cacopsylla pyri L. (Hemiptera: Psyllidae) is one of the most serious economic pear pests in Eastern Croatia. Previous methods of pear control in the Republic of Croatia have led to the development of an insect population resistan to certain active ingredients. The objectives of this two-year study were to determine the optimal number of treatments for psylla control based on the monitoring of pest life cycle and to determine the effectiveness of processed kaolin in controlling the pear psylla in comparison with other chemical insecticides in four different treatments (T1. IPM-integrated protection program – diflubenzuron, spirotetramat, abamectin, acetamprid; T2. acrinatrin + abamectin, T3. kaolin clay, T4. control treatment). The research was conducted in 2017 and 2018 in a six-year-old experimental pear orchard on three varieties (Williams, Conference, and Abate Fetel). Monitoring of the pest population and its development was performed by visual inspection on two one-year shoots per tree of each variety in all replicates. The T1 treatment demonstrated the highest efficiency, between 84-95%, depending on the year, while the kaolin treatment had the lowest one, but it varied greatly from one year to the other (37-71%).

High temperature has an adverse effect on apple production worldwide. Photosynthesis is a process especially vulnerable to heat stress, which can reduce photosynthetic efficiency, plant growth, development, and ultimately yield. Although the effects of heat stress on apples have been partially examined, the photochemical reactions and heat tolerance of specific rootstocks have still not been sufficiently investigated. Identification of rootstocks with better photosynthetic performance and adaptation to heat stress enables the selection of rootstocks, which could contribute to stable yields and good fruit quality even at elevated temperatures. In this study, chlorophyll a fluorescence (ChlF) induction kinetics was used to investigate the heat tolerance between two apple rootstocks (M.9 and G.210). In addition, we employed lipid peroxidation measurements, hydrogen peroxide quantification, proline content, and total phenolic and flavonoid assessments. Analysis of chlorophyll fluorescence parameters and OJIP curves (different steps of the polyphasic fluorescence transient; O–J–I–P phases) revealed significant differences in their responses, with higher values of the PI_ABS parameter indicating better PS II stability and overall photosynthetic efficiency in M.9 rootstock. The higher contents of chlorophyll, carotenoids, proline, and significant increase in the accumulation of phenolics, and flavonoids in this rootstock also contributed to its better adaptation to heat stress. Oxidative stress was more pronounced in G.210 through higher H₂O₂ and MDA levels, which could point to its lower capacity to adjust to heat stress conditions. This research can provide a scientific basis for further breeding programs and growing plans due to climate change and the occurrence of extremely high temperatures.