Partial Root-Zone Drying of Olive (Olea europaea var. "Chetoui") Induces Reduced Yield under Field Conditions

The productivity of olive trees in arid and semi-arid environments is closely linked to irrigation. It is necessary to improve the efficiency of irrigation techniques to optimise the amount of olive fruit produced in relation to the volume of water used. Partial root-zone drying (PRD) is a water saving irrigation technique that theoretically allows the production of a root-to-shoot signal that modifies the physiology of the above-ground parts of the plant; specifically reducing stomatal conductance (gs) and improving water use efficiency (WUE). Partial root-zone drying has been successfully applied under field conditions to woody and non-woody crops; yet the few previous trials with olive trees have produced contrasting results. Thirty year-old olive trees (Olea europaea ‘var. Chetoui’) in a Tunisian grove were exposed to four treatments from May to October for three-years: ‘control’ plants received 100% of the potential evapotranspirative demand (ETc) applied to the whole root-zone; ‘PRD100’ were supplied with an identical volume of water to the control plants alternated between halves of the root-zone every ten-days; ‘PRD50’ were given 50% of ETc to half of the root-system, and; ‘rain-fed’ plants received no supplementary irrigation. Allowing part of the root-zone to dry resulted in reduced vegetative growth and lower yield: PRD100 decreased yield by ~47% during productive years. During the less productive years of the alternate bearing cycle, irrigation had no effect on yield; this suggests that withholding of water during ‘off-years’ may enhance the effectiveness of irrigation over a two-year cycle. The amount and quality of oil within the olive fruit was unaffected by the irrigation treatment. Photosynthesis declined in the PRD50 and rain-fed trees due to greater diffusive limitations and reduced biochemical uptake of CO2. Stomatal conductance and the foliar concentration of abscisic acid (ABA) were not altered by PRD100 irrigation, which may indicate the absence of a hormonal root-to-shoot signal. Rain-fed and PRD50 treatments induced increased stem water potential and increased foliar concentrations of ABA, proline and soluble sugars. The stomata of the olive trees were relatively insensitive to super-ambient increases in [CO2] and higher [ABA]. These characteristics of ‘hydro-passive’ stomatal behaviour indicate that the ‘Chetoui’ variety of olive tree used in this study lacks the physiological responses required for the successful exploitation of PRD techniques to increase yield and water productivity. Alternative irrigation techniques such as partial deficit irrigation may be more suitable for ‘Chetoui’ olive production.This work was supported by the Ministero dell’Istruzione, dell’Università e della Ricerca of Italy: PRIN 2010–2011 “PRO-ROOT” and Progetto Premiale 2012 “Aqua”. MH acknowledges funding from a Marie Curie IEF (2010–275626). We are grateful to Dr Mohamed Ghrab (Olive Tree Institute) for technical assistance and scientific discussion. The comments of Georgios Koubouris (Hellenic Agricultural Organization) and two anonymous reviewers significantly improved this manuscript

Climate change and viability of fruit tree orchards in arid area

The Mediterranean region is facing temperature increases due to climate change. More warm conditions across the fruit and nut growing regions are expected to have a great and negative impact in Tunisian arid regions. Chilling trends among the agricultural production areas and their incidence on flowering and fruiting of typical fruit species were investigated. The results showed important declines in winter chill accumulation over the main arid production areas. This lack of chill jeopardizing the flowering and fruiting of fruit species. However, fruit species and cultivars within each fruit species expressed different flowering and fruiting behaviors to warm climate depending on their chilling and heat requirements. Consequently, thermal requirements are a key factor for sustainable fruit trees’ orchards and to select suitable cultivation area. Adoption of appropriate genetic resources could be used to mitigate the harmful effect of global warming in arid regions

Eco-physiological evaluation of different scion-rootstock combinations of almond grown in Mediterranean conditions

Introduction. Recent management trends in almond orchards have focused on intensification and high-density plantings using Prunus rootstock cultivars with different vigor traits. This investigation aims to prospect precocious detection of adequate scion-rootstock combination for almond. Materials and methods. Five almond cultivars (‘Tuono’, ‘Lauranne’, ‘Soleta’, ‘Belona’ and ‘Guara’) grafted on three peach and plum based rootstocks of different degrees of vigor (‘Garnem’, ‘Rootpac-40’ and ‘Rootpac-20’) were trained in super high-density planting in an experimental orchard. Tree vigor, tree water status, leaf chlorophyll content and quantum yield of photosynthesis system II (PSII) were monitored over two budding seasons. Results and discussion. ‘Garnem’ and ‘Rootpac-40’ were respectively the most and the medium vigorous rootstocks and induced the best tree water status, chlorophyll content and quantum yield of PSII for the tested almond cultivars. Scions grafted on ‘Garnem’ had the highest values of trunk cross-sectional area (TCSA), and almond scions were higher on ‘Garnem’, intermediate on ‘Rootpac-40’ and lower on ‘Rootpac-20’. Scions grafted on ‘Rootpac-20’ seemed to be the most dwarf phenotype. Moreover, ‘Rootpac-20’ performed the lowest values of stem water potential and showed various visual symptoms of chlorosis. Conclusion. Overall, ‘Rootpac-40’ exhibited a medium capacity to control tree vigor and well adapted to Mediterranean soil conditions

Responses of olive trees (cv. Chemlali) after five years of experiment to potassium mineral nutrition under rainfed condition

Optimal potassium nutrition is essential to maximize olive tree production. In Tunisia, olive trees are mainly conducted under rainfed conditions and subjected to water and nutrient deficits. An experiment was established in semi arid region to study the response of olive tree to potassium mineral nutrition using potassium sulphate in reference to Control. Potassium was supplied by foliar spray and soil spreading at two levels. Foliar treatments were 50 and 100% of tree requirement. For soil spreading, 100% and 200% of the tree needs were applied. After five of experiment, yield was significantly higher for 100% foliar spray than the control. Leaf mineral analysis revealed a significant increase of K foliar content in response to K supply. Foliar nutrition at 100% of tree needs improved the cumulative yield and olive quality. An increase of average fruit weight, pit ratio was observed for foliar spray treatment. However, oil quality seems to be unaffected with insignificant differences of poly phenols content and fatty acid composition

Responses of olive trees (cv. Chemlali) after five years of experiment to potassium mineral nutrition under rainfed condition

Optimal potassium nutrition is essential to maximize olive tree production. In Tunisia, olive trees are mainly conducted under rainfed conditions and subjected to water and nutrient deficits. An experiment was established in semi arid region to study the response of olive tree to potassium mineral nutrition using potassium sulphate in reference to Control. Potassium was supplied by foliar spray and soil spreading at two levels. Foliar treatments were 50 and 100% of tree requirement. For soil spreading, 100% and 200% of the tree needs were applied. After five of experiment, yield was significantly higher for 100% foliar spray than the control. Leaf mineral analysis revealed a significant increase of K foliar content in response to K supply. Foliar nutrition at 100% of tree needs improved the cumulative yield and olive quality. An increase of average fruit weight, pit ratio was observed for foliar spray treatment. However, oil quality seems to be unaffected with insignificant differences of poly phenols content and fatty acid composition

Abscission of orange fruit (Citrus sinensis (L.) Osb.) in the Mediterranean basin depends more on environmental conditions than on fruit ripeness

Orange fruit abscission usually occurs at the final stage of fruit maturation but in some areas of citrus production, in advance of the usual harvest period, and sometimes suddenly and intensely. The reasons for this precocious citrus fruit abscission remains unclear. Therefore, the aim of this study was to try to clarify what the determinants of this phenomenon are. A multi-site experimentation was carried out on six orange cultivars, in Corsica, Spain and Tunisia where the phenomenon of early massive fruit drop varies. Climatic parameters, fruit maturity parameters and fruit detachment force (FDF) were recorded along the fruit maturation period. Respectively to the fruit drop, the FDF decreased in Tunisia and in Spain until the fruit falls, whereas in Corsica, it remained relatively constant throughout fruit maturation. Although data on fruit maturity parameters (rind color, acidity and total soluble solids) differed at the three sites, their evolution was similar during the period of maturation. FDF was not related to changes in any fruit maturity parameters, and more likely depended on changes in temperatures on days when the mean temperature was above 13 °C. Massive fruit abscission could be linked to the earlier more rapid restart of vegetative growth in Tunisia and Spain than in Corsica

Abscission Study during Citrus Fruit Maturation in Corsica: Unfavorable Environmental Conditions for Fruit Shedding

International audienceCitrus fruit development and ripening are complex processes involving physiological and biochemical changes that are under hormonal, nutritional and environmental control. One of the most evident phenomena in late maturation is shedding of ripe fruit. A study made in Spain on sweet oranges showed that fruit shedding was related to the increase of sugars content of fruit pulp juice. To investigate this potential relationship between fruit abscission and internal maturity parameters we investigated the fruit maturity process of 10 clementine x mandarin hybrids and 9 commercial sweet orange varieties with different maturity period. Morphological and biochemical analyses (acidity, total soluble solids, fruit weight thickness of the flavedo, thickness of the peduncle, external colo) were carried out on fruit sets of the different varieties during the maturation process, from December to June. The abscission initiation was evaluated by measuring the force required to detach the fruit of the peduncle. Analysis showed that under the local conditions, abscission was generally not expressed even through fruit maturation was evolving. Therefore, we suppose that even though the local conditions have an important effect, abscission of citrus fruit results also from environmental-genotype interactions. Moreover, evolution of abscission and fruit parameters are not correlated suggesting the independence in the process of maturation and abscission under the environmental conditions of Corsica