How Temperatures May Affect the Synthesis of Fatty Acids during Olive Fruit Ripening: Genes at Work in the Field

A major concern for olive cultivation in many extra-Mediterranean regions is the adaptation of recently introduced cultivars to environmental conditions different from those prevailing in the original area, such as the Mediterranean basin. Some of these cultivars can easily adapt their physiological and biochemical parameters in new agro-environments, whereas others show unbalanced values of oleic acid content. The objective of this study was to evaluate the effects of the thermal regime during oil synthesis on the expression of fatty acid desaturase genes and on the unsaturated fatty acid contents at the field level. Two cultivars (Arbequina and Coratina) were included in the analysis over a wide latitudinal gradient in Argentina. The results suggest that the thermal regime exerts a regulatory effect at the transcriptional level on both OeSAD2 and OeFAD2-2 genes and that this regulation is cultivar-dependent. It was also observed that the accumulated thermal time affects gene expression and the contents of oleic and linoleic acids in cv. Arbequina more than in Coratina. The fatty acid composition of cv. Arbequina is more influenced by the temperature regime than Coratina, suggesting its greater plasticity. Overall, findings from this study may drive future strategies for olive spreading towards areas with different or extreme thermal regimes serve as guidance for the evaluation olive varietal patrimony.

Olive oil characterization of cv. 'Arauco' harvested at different times in areas with early frost in Mendoza, Argentina

BACKGROUND

'Arauco' is the only autochthonous olive cultivar from Argentina. Little has been reported so far regarding the management of this crop. In this work, variations in fruit and chemical characteristics of olives harvested over a wide range of dates and seasons are reported for this cultivar at two sites in Mendoza province in central west Argentina.

RESULTS

During the harvest periods studied, fruit oil content on a dry basis remained at its maximum and was stable, but fruit oil content on fresh basis increased as water content decreased with delay in harvest date. Harvest date affected the maturity index of fruits as well as the oxidative stability and phenolic content of oil. In contrast, the fatty acid profile was not consistently affected by harvest date. Environmental conditions, mainly the occurrence and intensity of frosts, strongly influenced oil quality as well as maturity with delay in harvest date.

CONCLUSION

The most appropriate harvest time to obtain Arauco oil with a high oil yield and good chemical quality was before mid-May and with maturity index lower than 2. Fruits harvested after mid-May were exposed to minimum temperatures between -1.2 °C and - 4.0 °C, producing oil with low phenolic compounds and oxidative stability. © 2019 Society of Chemical Industry.

Multi-environment evaluation of oil accumulation pattern parameters in olive

The pattern of olive oil accumulation is of paramount importance in olive because its influence in determining final oil yield and optimal harvesting date. In this work, we have evaluated the genetic and environment influence on the olive oil accumulation pattern. For that purpose, a set of cultivars and breeding selections planted in a multi-environment trial was evaluated in two consecutive harvest seasons. Significant effect of the environment, genotype and their interaction were observed for the maximum oil content reached and the rate of oil accumulation. On the contrary, the date of maximum oil content seems to depend only on the environment. The two breeding selections evaluated showed, in general, high stability and adaptability in oil accumulation parameters. Among the potential environmental factors that could affect oil accumulation, PLS analysis suggests that temperature could play a determinant environmental effect in the oil accumulation parameters tested in this study. These results underline the relevance of using multi-environment trials for adequate characterization of genotypes showing either good behaviour in variable environments or only under specific environmental conditions.

Long-term Effect of Intra-Row Spacing on Growth and Productivity of Super-High Density Hedgerow Olive Orchards (cv. Arbequina)

Intra-row spacing is known to determine early productivity of super-high density olive orchards depending on growing conditions, cultivar growth characteristics, planting geometry and subsequent pruning management but few experiments have been carried out in this olive hedgerow orchard design. In 2008 an experiment of 4-m spaced hedgerows was established with 8 intra-row spacings (from 1.0 to 2.5 m) in Toledo (Spain) resulting in orchards of density ranging from 2,500 to 1,000 trees ha^-1. Tree growth was evaluated as height, trunk diameter and leaf area during the first 4 years. Hedgerow porosity was calculated from the 4th until the 9th year. In the 8th year hedgerow height, width, leaf area and branch angles were measured. Olives were harvested from 3rd to 9th year for measurements of fruit characteristics and productivity. Tree growth was not affected by intra-row spacing during the first 4 years. In the 8th year leaf area, external surface area and volume per tree were significantly greater in the more spaced trees; but hedgerow characteristics of leaf area per hectare, number of effective leaf layers horizontally through the hedgerow, and leaf density were not affected. In the more spaced trees insertion angles of branches to the vertical were significantly greater, mainly in the lower canopy. Intra-row spacing did not affect fruit characteristics. Oil production ha^-1 decreased linearly with spacing during the first 4 harvests while production per tree increased significantly with spacing after the 3rd harvest. As a result, oil production ha^-1 from the seven harvests combined only increased for tree spacing less than 1.2 m; wider spacing had no effect. Annual oil production ha^-1 increased linearly as porosity was reduced by greater tree density and canopy development along the seasons.

Effects of the source:sink ratio on the phenotypic plasticity of stem water potential in olive (Olea europaea L.)

The aims of this work were to quantify (i) the effect of the source:sink ratio on stem water potential (SWP) and (ii) the phenotypic plasticity of SWP and its relationship to oil yield components in olive. Trees with a 3-fold variation in the source:sink ratio (crown volume/fruit number per tree) were monitored in 2007-2008 and 2008-2009 in a fully irrigated orchard in Mendoza, Argentina. The combination of rainfall, irrigation, and evaporative demand led to a steady SWP largely above -1.65 MPa in 2007-2008 and a marked seasonal decline from -1.13 MPa to -2.04 MPa in trees with a medium and low source:sink ratio in 2008-2009. Plasticity was quantified as the slope of the norm of reaction for each trait. Across seasons, trees with a high source:sink ratio had a higher SWP than their counterparts with a medium and low source:sink ratio. Plasticity of SWP was highest in olives with a low source:sink ratio (slope=1.28) and lowest for trees with a high source:sink ratio (slope=0.76). The average SWP for each source:sink ratio and season was unrelated to both the source:sink ratio and yield components. On the other hand, the plasticity of SWP was positively associated with fruit number and negatively associated with the source:sink ratio, fruit weight, and fruit oil weight. The plasticity of the SWP was unrelated to SWP per se. It is concluded that understanding the effect of the source:sink ratio on plant water relations would benefit from a dual perspective considering the trait per se and its plasticity. A dual approach would also allow for more robust plant-based indicators for irrigation.

Phenotypic plasticity of stem water potential correlates with crop load in horticultural trees

Conceptual models accounting for the influence of source:sink ratio on water relations of trees are theoretically relevant from a physiological perspective and practically important for irrigation scheduling. Midday stem water potential of horticultural trees often declines with increasing crop load but the actual response depends on environmental, management and plant factors. Here we advance a quantitative synthesis of the response of stem water potential to crop load from the perspective of phenotypic plasticity, defined as 'the amount by which the expression of individual characteristics of a genotype are changed by different environments'. Data sets of stem water potential for contrasting crop loads were compiled for apple (Malus domestica L. Borkh.), olive (Olea europea L.), peach (Prunus persica L.), pear (Pyrus communis L.) and plum (Prunus domestica L.). Phenotypic plasticity of stem water potential was calculated as the slope of the linear regression between stem water potential for each crop load and the environmental mean of stem water potential across crop loads. Regression lines for trees with different crop load diverged with decreasing environmental mean stem water potential. For the pooled data, plasticity of stem water potential was a linear function of relative crop load. This represents a significant shift in perspective: the effect of crop load on the trait per se (stem water potential) is environmentally contingent, but the effect of crop load on the plasticity of the trait is not. We conclude that research on the effects of crop load on tree water relations would return more robust results if plant traits are considered from the dual perspective of the trait per se and its plasticity.