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In recent years, many farmers use new types of fertilizers to enhance fruit set and development and enhance the resilience of olive trees to climate change. In parallel, NO3− leaching in the soil and water threat the environment pointing toward a more sustainable nutrient management. This study investigated the effect of AMINO-16©, a commercial product derived from hydrolysis/extraction of protein-rich plant material and contains sixteen L-amino acids, on vegetative growth, flowering, nutritional status, yield, and oil qualitative characteristics of 'Koroneiki' olives on the Mediterranean island of Crete in Greece. We conducted a field experiment with amino acid foliar sprays for two growing seasons in a commercial irrigated olive grove. Treatments comprised (a) no amino acid application (Control), (b) three applications (summer 2014, winter 2015, and spring 2015) of AMINO-16 (A16-A), and (c) one application (winter 2015) of AMINO-16 (A16-B). The A16-A treatment (three sprays) significantly increased the number of inflorescences, the fruit set, and the number of fruits per shoot. Fruit yield and olive oil yield were higher than those of the control by 10.6 and 18%, respectively. In addition, leaf nutrient levels and the quality characteristics of olive oil in both treatments were not differentiated from the control. Overall, foliar fertilization with amino acids could enhance plant growth. Future research using amino acids at different reproductive and vegetative stages of olive trees is likely to further improve olive oil yield and quality. [ABSTRACT FROM AUTHOR]

The olive tree (Olea europaea L.) is the main fruit tree in most of the arid and semi-arid regions of Tunisia, which is where the problem of salinity is more pronounced. Salinity is one of the main factors that affects the productivity of olive trees, so the objective of this experiment was to study the effects of salinity on the photosynthesis, water relations, mineral status, and enzymatic activity of two cultivars of Olea europaea L., 'Chemlali' and 'Koroneiki'. The trial was conducted under controlled conditions in a greenhouse for a period of 49 days and included two treatments: T0 control and T100 (irrigation with 100 mM of NaCl solution). Under salinity stress, the photosynthesis, stomatal conductance, and leaves of both cultivars were negatively affected. 'Chemlali' showed greater tolerance to NaCl salinity, based on a progressive decrease in osmotic potential (Ψπ) followed by a progressive and synchronous decrease in gs, without a comparable decrease in photosynthesis. The water use efficiency (WUE) improved as a result. In addition, the K+/Na+ ratio in 'Chemlali' rose. This appears to be crucial for managing stress. Conversely, enzymatic activity showed an accumulation of glutathione peroxidase (GPX) in stressed plants. The catalase (CAT) and ascorbate peroxidase (APX) content decreased in both stressed varieties. It can be concluded that the cultivar 'Koroneiki' is more susceptible to salt stress than the cultivar 'Chemlali', because the accumulation of GPX and the decreases in CAT and APX were more pronounced in this cultivar. [ABSTRACT FROM AUTHOR]

Olive cultivation in hot arid areas is hindered by the scarcity of irrigation water. The exploitation of saline water has been proposed as a solution to partially cover plant water demands. This paper presents the effects of salinity [0, 60 and 120 mM sodium chloride (NaCl)] on physiological and reproductive functions of cultivars Koroneiki and Amphissis in a closed hydroponic system. Shoot growth was markedly reduced in high salinity dose in Amphissis (-81%) and Koroneiki (-75%). The photosynthetic rate was significantly reduced at 120 mM NaCl for both cultivars, as well as chlorophyll and carotenoids content (43% and 44%, respectively). The Na+ content in all plant parts increased in both salinity doses especially in Amphissis while K concentration decreased for both cultivars. Inflorescences in Amphissis were severely damaged due to salinity. Consequently, pollen sampling and in vitro germination study was only feasible for Koroneiki. Indeed, Koroneiki pollen germination was reduced at 60 mM NaCl (-42%) and at 120 mM NaCl (-88%). Pollen tube length was also reduced by 15% and 28% for the middle and high salinity dose, respectively. The results of the present study indicate that Amphissis is more sensitive in high salinity doses compared to Koroneiki and that reproductive functions are severely affected by salinity. [ABSTRACT FROM AUTHOR]

The olive tree (Olea europaea L.) is one of the main crops of the Mediterranean region which suffers from drought and soil salinization. We assessed the photosynthetic rate, leaf water content and antioxidative enzyme activity (APX, GPX, SOD and CAT) of three Greek olive cultivars ('Amfisis', 'Mastoidis' and 'Lefkolia Serron') subjected to drought and salinity stresses. Hyperspectral reflectance data were acquired using an analytical spectral device (ASD) FieldSpec® 3 spectroradiometer, while principal component regression, partial least squares regression and linear discriminant analysis were used to estimate the relationship between spectral and physiological measurements. The photosynthetic rate and water content of stressed plants decreased, while enzyme activity had an increasing tendency. 'Amfisis' was more resistant to drought and salinity stress than 'Mastoidis' and 'Lefkolia Serron'. The NDVI appeared to have the highest correlation with the photosynthetic rate, followed by the PRI. APX enzyme activity was the most highly correlated with the 1150–1370 nm range, with an additional peak at 1840 nm. CAT enzyme activity resulted in the highest correlation with the visible part of the spectrum with two peaks at 1480 nm and 1950 nm, while GPX enzyme activity appeared to have a strong correlation within all the available spectral ranges except for 670–1180 nm. Finally, SOD activity showed high correlation values within 1190–1850 nm. This is the first time the correlation of hyperspectral imagery with photosynthetic rate and antioxidant enzyme activities was determined, providing the background for high-throughput plant phenotyping through a drone with a hyperspectral camera. This progress would provide the possibility of early stress detection in large olive groves and assist farmers in decision making and optimizing crop management, health and productivity. [ABSTRACT FROM AUTHOR]

Olive tree growth and reproduction are severely affected by temperature extremes, compromising fruit yield. In that aspect, the olive varieties "Koroneiki" and "Mastoidis" were employed in a mild cold stress experiment, imitating night frost incidents to assess their biochemical, physiological and reproductive functions in relation to genotype. The physiological performance of the stressed plants was not significantly altered, suggesting that both cultivars were well adapted to mild cold night stress. The biochemical response of the plants, regarding antioxidant enzymes, H2O2 and TBARS accumulation, confirmed that both cultivars could cope with the stress applied. The mRNA levels of the PPO gene, which participates in hydroxytyrosol biosynthesis and plant defense, were elevated after 24-h stress at 0 °C, in both cultivars with "Mastoidis" plants exhibiting higher levels for a longer period. Three more genes involved in hydroxytyrosol biosynthesis upregulated their expression levels as a response to cold stress. The numerous plant phenology aspects measured reinforced the conclusion that both cultivars responded to the stress applied. The results of the present study may contribute to better understanding olive tree adaptive responses to low temperature events, an abiotic stress condition that is often present in an open plantation, thus assisting farmers on breeding and cultivar selection. [ABSTRACT FROM AUTHOR]

• Salinity treatments induced negative effects on photosynthesis, stomatal conductance, leaf chlorophyll index, plant growth and dry matter accumulation for both cultivars. • 'Chemlali' has a higher resistance to increasing NaCl salinity. • Mannitol accumulation increased under salinity stress for 'Chemlali' and seems to play a major role in stress tolerance. • GA3 application alleviated the negative effects of salt stress on the ecophysiological parameters especially for 'Koroneiki'. Soil salinization is considered as one of the most important risks for agricultural soils. The objective of this experiment was to study the ecophysiological and the biochemical behaviour of two cultivars of Olea europaea L., 'Chemlali' and 'Koroneiki' under two salinity levels (100 and 200 mM NaCl) and the potential alleviation induced by gibberellic acid (GA3) foliar sprays. Salinity treatments significantly decreased photosynthetic assimilation rate and stomatal conductance compared to the control for both cultivars, but 'Chemlali' showed a higher resistance to increasing NaCl salinity compared to 'Koroneiki'. Leaf chlorophyll index also reduced gradually with increasing salinity concentration compared to the control. At the end of the experiment, a decrease in growth and dry matter accumulation was observed. Under high salinity stress, a significant decrease in root DW was recorded by 37% and 59% for 'Chemlali' and 'Koroneiki', respectively. High salinity stress decreased also shoot DW up to 51% for 'Chemlali'. However, mannitol concentration increased under increasing salinity levels compared to control for 'Chemlali' cultivars. Interestingly, foliar application of GA3 alleviated the negative effects of salinity on ecophysiological parameters especially for 'Koroneiki'. Indeed, GA3 improved photosynthetic assimilation up to 14% for 'Chemlali' and 36% for 'Koroneiki' compared to high salinity treatment. Both cultivars showed an increase in leaf chlorophyll index after applying GA3. Under high salinity combined with GA3, growth and dry weight were increased compared to salt stressed plants without GA3. The obtained results report that 'Chemlali' cultivar is more tolerant to salinity than 'Koroneiki' and suggest that GA3 plays an important role to reduce negative effects of NaCl salinity. [ABSTRACT FROM AUTHOR]