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BACKGROUND: Kiwifruit plants are extremely sensitive to hail storms. Black anti-hail nets are the most frequently used in kiwifruit culture, to protect both the plant and current as well as future production. OBJECTIVE: The present trial aimed to assess if the black hail net could also serve as an amelioration agent against high temperature and irradiance during the summer months. METHODS: The photosynthetic capacity, the yield, and fruit quality (carbohydrates, organic acids, phenolic compounds, and antioxidant capacity) of “Hayward” kiwifruit cultivar, both at harvest and after three months of storage were evaluated. RESULTS: Photosynthetic capacity under the net was slightly higher compared to control, while leaf temperature was always lower during the summer and autumn. The yield was significantly enhanced under the net, while the fruits exhibited higher titratable acidity, organic acids, and ascorbic acid concentration. After the storage, fruits produced from vines grown under net still had higher organic acid content, as well as total soluble solids but lower antioxidant capacity compared to control. CONCLUSIONS: Net installation above kiwifruit canopy seems to alleviate the effects of high temperature and heat load on kiwifruit vines, under saturating light intensity, inducing higher yields with good fruit quality.

BACKGROUND: Strawberry is usually cultivated in unheated glasshouses or outdoors, suffering many times by low temperatures during the winter period, with the danger of plant losses. OBJECTIVE: To investigate the efficacy of various alleviating agents against chilling and freezing stress. METHODS: Strawberry plants were foliarly treated with various alleviating substances, i.e. glycine betaine, trehalose, salicylic acid and proline and exposed to 5 °C (chilling treatment) for three weeks followed by a three hour exposure to – 10 °C (freezing treatment), while control plants were growing under 20 °C. At the end of each period polyamine and carbohydrate concentration, antioxidant enzymes activities, total phenols and proline concentration, chlorophyll concentration, lipid peroxidation, electrolyte leakage and H2O2 production in the leaves were measured. RESULTS: All applied products alleviated chilling stress, inducing lower electrolyte leakage, but higher sucrose and fructose concentration in the leaves compared to control. Under freezing temperature, salicylic acid proved to be the most efficient based on the lowest leaf damage observed, followed by trehalose and proline. CONCLUSIONS: Salicylic acid was the best alleviation agent based on leaf damage evaluation, by inducing low chlorophyll a degradation, low superoxide dismoutase, peroxidase and polyphenol oxidase activities as well as low putrescine concentration.

Strawberry, the most significant berry crop, is characterized as a salt-sensitive plant. The present study aimed to examine ways to alleviate salinity symptoms (34 mM of NaCl in irrigation water) in strawberry plants. For this purpose, the osmolyte glycine betaine was foliarly applied, a mixture of bentonite–zeolite was added to the substrate, and a microbial product based on Bacillys amyloliquefaciens as a soil drench were tested in terms of plant growth and nutrient status, yield, fruit physiological and organoleptic characteristics, as well as phytochemical properties (phenolic compounds, carbohydrates, organic acids, anthocyanins, and antioxidant capacity), and soil physicochemical properties. Salinity severely reduced plant growth and yield, while the effects on fruit quality were also distinct. Treatments alleviated to some extent these negative effects. Plant nutrient content was not severely affected by product application, and neither were most of the soil physicochemical properties. Among the products applied, the mixture of bentonite plus zeolite and glycine betaine proved to be more efficient in ameliorating toxicity symptoms, as both treatments preserved plant hydric status and plant growth, while glycine betaine resulted in an almost 30% higher yield than the treatment with saline water.

The objective of this study was to role the effect of phenolic compounds on the rooting potential of leafy cuttings of the recalcitrant to root olive cultivar ‘Kalamata’ and the easy to root ‘Arbequina’. Subsamples of cuttings were taken for analysis before planting (day 0) in the mist system and during the early phases of rhizogenesis (EPR). ‘Kalamata’ presented higher initial (day 0) total phenols in summer and total o-diphenols in autumn and spring compared to ‘Arbequina’, while ‘Arbequina’ had significantly higher initial total flavonoids and flavanols in autumn. A positive correlation was found between initial total phenols and rooting ability of ‘Arbequina’. In ‘Kalamata’ a positive correlation was established between initial total o-diphenols and rooting percentage while total flavonoids were negatively correlated with rooting. Generally, total phenols, o-diphenols, flavanols and flavonoids did not differ between the two cultivars and their concentration reduced significantly 15 days after planting. Furthermore, ‘Arbequina’ presented higher initial tyrosol, chlorogenic acid, luteolin-7-glucoside, rutin, quercetin and luteolin in summer and autumn compared to ‘Kalamata’. The above phenolics were positively correlated with the rooting of ‘Arbequina’. Significant changes were observed in the concentration of the individual phenolics during the EPR, whereas chlorogenic acid, rutin, quercetin and luteolin concentration increased significantly from day 1 to 5. In conclusion, there is a clear relationship between the phenolic profile and adventitious rooting of the two olive cultivars and in fact chlorogenic acid and rutin can be proposed as olive rooting enhancers.

Two plant growth regulators (PGRs), one auxin analog i.e. triclopyr and one cytokinin i.e. forchlorfenuron were applied on two apricot cultivars (“Nafsika” and “Niovi”) during the early stages after fruit set (cytokinin) and at the beginning of pit hardening (auxin). The two PGRs were applied either alone or in combination, each at the time indicated above. The fruit growth rate along with fruit physiological, organoleptic and phytochemical characteristics was assessed during two successive years. In all treatments where auxin was included, the growth rate of the fruits was significantly enhanced. Fruit weight increased significantly with auxin (by 30% in “Niovi” and 34% in “Nafsika”), as well as the diameter in chicks and suture line along with fruit length, without altering fruit shape, as confirmed by fruit shape index and sphericity calculations. Although the concentration of carbohydrates was not significantly different among treatments, the overall carbohydrate content of the fruit was significantly enhanced by auxin application. Total phenolic compounds as well as individual phenolic ones and antioxidant capacity of the fruit were not influenced by PGRs application. Cytokinin did not enhance fruit quality parameters, while at the same time retarded maturation, as the fruits retained the green color, firmness was quite high as were also the total organic acids and titratable acidity. The present findings support even further the use of auxin as the PGR of choice for stone fruits and especially for apricot, while cytokinin do not seem to be able to improve fruit quality characteristics.

Aim of study: To assess the role of polyphenol oxidase (PPO), peroxidase (POD) and indole-3-acetic acid oxidase (IAAox) during adventitious rooting (Ar) in semi-hardwood cuttings of the easy-to-root olive cv. ‘Arbequina’ and the difficult-to-root cv. ‘Kalamata’. Simultaneously, a histological study was carried out in both cultivars to investigate the tissue related with Ar development. Area of study: The rooting experiments were carried out in ‘Kostelenos’ nurseries (Troizinia, Greece) and in Agricultural University of Athens. Material and methods: Plant material to set up the experiment was collected from current year shoots from 15-year-old mother plants of ‘Arbequina’ and ‘Kalamata’ at three different seasons (summer, autumn and spring). The auxin indole-3-butyric acid (IBA) at 2000 mg L -1 was used as rooting inducer. Main results: Analysis revealed that ‘Kalamata’ had significantly higher enzymatic activities before experiment onset and during Ar compared to ‘Arbequina’. Control cuttings of both cultivars exhibited increased enzymatic activities compared to IBA treated ones. IAAox was on average three times higher in ‘Kalamata’ than in ‘Arbequina’ and exhibited significant peaks during Ar. Similar peaks of POD and PPO activities were also detected. Histological analyses in ‘Kalamata’ revealed a continuous sheath of sclerenchyma ring and increased cortex thickness. Significant cell proliferation occurred in the phloem region in ‘Arbequina’ 15 days after planting and afterwards the root initials started developing in the secondary phloem from cambial cells. Research highlights: The differences in enzymatic activities as well as in stem anatomy could partly justify the different rooting ability of both cultivars.

Two years old “Koroneiki” olive trees were subjected to drought stress after foliar application of products with known ameliorating function, i.e. glycine betaine (GB), kaolin clay particles (KL) and 5‐hydroxybenzimidazole (Ambiol). Measurements were taken after product application, within the stress period and after re-watering. Lipid peroxidation and electrolyte leakage, as well as antioxidant defence factors (enzymes such as catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD), guaiacol peroxidase (POD), glutathione reductase (GR) and phenolic compounds and ascorbic acid) were assayed. Drought induced a significant increase of lipid peroxidation and an elevation of the activity of SOD, POD and APX, while a drastic rise of oleuropein was also determined. KL application resulted in increased total phenol concentration as well as an increased activity of SOD, POD under drought. GB application increased the concentration of total flavanols during the drought period while right after application a sharp increase of oleuropein concentration was detected. Ambiol application decreased the total phenol concentration during the stress period, but enhanced POD and APX activity and total ascorbic acid concentration. During the relief period few significant differences were determined. All products alleviated to some degree the stress imposed by water deprivation, with Ambiol and KL being more efficient in preventing oxidative damage of olive trees. Based on the present results it could be assumed, that the combined use of alleviating products with different mode of action, could trigger multiple defence mechanisms, resulting in more efficient mitigation of abiotic stress.

The aim of the present study was to investigate the effects of exogenous application of kaolin clay particles, glycine betaine and Ambiol on olive (Olea europaea L.) plants subjected to drought stress. Two years old self-rooted cv. Chondrolia Chalkidikis olive trees were subjected to two irrigation regimes, i.e. the fully irrigated and the water stressed trees, while they were treated with the three pre-mentioned products. Drought decreased the relative water content, the actual water content and the succulence of leaves significantly, while leaf tissue density was increased. Carbon assimilation rate, stomatal conductance and intrinsic water use efficiency were significantly reduced under drought stress conditions, while intercellular CO2 increased. Among the alleviating products tested, kaolin clay particles had a significant positive effect on leaf water content, succulence, leaf tissue density and leaf temperature under both drought and well irrigated conditions. Glycine betaine and kaolin clay particles when applied to drought stressed trees, resulted in increased CO2 assimilation rates compared to control. Furthermore, kaolin clay particles treated leaves exhibited high diurnal CO2 assimilation rates under drought conditions. Based on the results of the present study, kaolin clay particles and glycine betaine proved to be the most effective, among the applied products, on alleviating the negative effects of drought stress.

Rooting experiments were performed in two seasons (summer and autumn, 2008). The effect of two rooting media (organic and a mixture of peat:perlite, 1:1), two hormones (IBA and NAA) at four different concentrations (500, 1000, 2000, 4000 ppm), and the combinations of these hormones on rooting ability of three olive cultivars ('Arbequina', 'Kalamata' and 'Mastoidis') was studied. Starch and sugar analyses of the base of cuttings were performed at 0, 3 and 7 days after they were put under a mist propagation system. The results showed that cuttings of the three cultivars rooted better in the organic substrate. 'Arbequina' gave the highest percentage of rooted cuttings (up to 96%), followed by 'Mastoidis' (up to 60%) and 'Kalamata' (2-5%). Hormone treatment affected the rooting ability of cultivars differently. Thus, 'Arbequina' had the highest rooting percentage with IBA (2000 ppm) in summer and IBA+NAA (1000 ppm) in autumn. NAA (1000 ppm) gave the best results for both seasons in 'Mastoidis' cultivar while IBA (500 ppm) gave the highest rooting percentage in 'Kalamata' (5% in summer). Initially, 'Arbequina' had higher stachyose, mannitol and total soluble sugar concentrations than the other cultivars, while 'Kalamata' had the highest starch concentration. The pattern of changes in sugar concentrations at 3 and 7 days after planting was different for each cultivar. Initial internal sugar concentrations and their metabolism might be important during the early period of the rooting process.

Three apricot (Prunus armeniaca L.) cultivars were subjected to different degrees of fruit thinning during pit hardening. At harvest fruit quality characteristics were assessed, along with phytochemicals’ concentration, such as carbohydrates, phenolic compounds and organic acids. Antioxidant capacity of the pulp was estimated by diphenyl picryl hydrazyl and ferric reducing antioxidant power assays. Thinning improved fruit weight in two of the three cultivars with a subsequent decrease in fruit firmness, without significant effect on total soluble solid content and titratable acidity. The skin color was not influenced by thinning, but carbohydrate concentration and sweetness index increased. Total phenol concentration increased with thinning, without any similar increase of the major individual phenolic compounds detected (neo-chlorogenic acid, chlorogenic acid, rutin, catechin, epicatechin, ferulic acid, p-coumaric acid and caffeic acid). The antioxidant capacity of the pulp was not influenced by thinning. In overall, thinning enhanced the pomological traits of apricot fruits as well as their phytochemical content.

Two years old self-rooted Koroneiki olive trees (Olea europaea L.) were subjected to two irrigation regimes, i.e. the fully irrigated and the severely water stressed trees, while they were treated with three alleviating products of different mode of action. The products used were the osmolyte glycine betaine, the antioxidant Ambiol and the heat and irradiance reflecting kaolin clay particles. The effects of product application and water regime on leaf characteristics, shoot and root growth, photosynthesis, leaf compatible solids (carbohydrates) concentration and yield were evaluated. All products applied, exhibited significant alleviating action, based on the relative alleviation index. Irrigated trees exhibited greater growth than drought stressed ones, while the ameliorating products maintained the water content of the leaves under drought conditions and resulted in lower leaf tissue density. On the other hand carbon assimilation rate, stomatal conductance and intrinsic water use efficiency were significantly reduced under drought stress, while the opposite stood for intercellular CO2. Drought stress resulted in elevated sucrose leaf concentration, while the application of Ambiol increased stachyose concentration and that of glycine betaine did the same with the mannitol concentration. Among the alleviating products tested in this experiment Ambiol and glycine betaine had a significant positive effect on leaf water content, photosynthesis and yield under both drought and well irrigated conditions.

Strawberry plants cv. Camarosa were treated with different plant growth stimulators, in order to examine their effect on both yield and product quality. The treatments comprised an untreated control and a mixture of a seaweed extract plus a commercial mixture of nitrophenolates and a commercial mixture of an auxin (phenothiol) plus gibberellic acid at two dose rates. The plant growth stimulators increased marketable yield and fruit size, while they had no significant impact on fruit juice pH, titratable acidity and total soluble solids concentration. Furthermore, they had no significant effect on fruit organic acid and carbohydrate concentration and on fruit color, although they enhanced total anthocyanin concentration. The antioxidant activity of the fruit juice was slightly higher in the fruits of control treatment, which could be the result of their higher total phenol, o-diphenol, flavonoid and flavanol concentration. When a taste panel took place, the panelists gave the best score to those fruits deriving from plants treated with the mixture of auxin plus gibberellic acid.

Plum is highly appreciated by consumers, both as fresh for its characteristic taste and as dry for its action as a natural laxative. It is rich in sucrose, fructose, and glucose, with the dominant carbohydrate differing among cultivars. Plums are rich in anthocyanins, mainly cyaniding-3-glucoside and cyaniding-3-rutinoside, with their concentration differing among cultivars, giving the fruit its characteristic color. The majority of the anthocyanins are found in the peel, where high amounts of procyanidins are also present. Chlorogenic acid and neochlorogenic acid are the major phenolic compounds, with great differences in concentration among cultivars. The major vitamin is ascorbic acid, and β-carotene is the dominant carotenoid present. The distinctive aroma of plum fruits is the result of various volatile compounds differing among cultivars, with the major ones being hexanal, butyl acetate, (E)-2-hexenal, butyl butyrate, hexyl acetate, linalool, 1-hexanol, nonanal, γ-decalactone, γ-dodecalactone, and (Z)-3-hexen-l-ol.