Factors affecting olive fruits and oil production

Olive trees nowadays

Olive is one of the main species grown in the Mediterranean basin, especially in less-favored areas. However, olive oil which derives from olive tree fruits crush and often called “green gold”, not only because of its relatively high price compared to other oils used for human nutritional needs, but also because of the high nutritional value that characterizes it. In addition, the cost of all required work related to the production of olive oil remains high, even over 50% of the total cost of production. Therefore, it is still necessary to obtain a deeper knowledge about cultivation treatments in olive groves, which, as mentioned below, are mainly aimed at increasing the yield of olives and consequently the increased production of olive oil.

Factors affecting olive groves productivity

Irrigation

Although it is possible to cultivate olive trees even in areas characterized by the presence of arid climate, the provision of water, especially in critical periods such as hardening of the core, has a positive effect on the productivity of olive trees. More specifically, some scientists claim that Frantoio trees grown in places located on Mediterranean climate zone planted in rows at 5×3.9m distances and adequately irrigated are more efficient, at least in terms of the number of olives harvested and the amount of olive produced. However, some scientists claim that irrigation has only favored the number of olives harvested and their average fresh weight. Nevertheless, the same tension was not observed in the oil content of the olives, which was reduced compared to other interventions involving the irrigation of olive trees at different intervals throughout the experiment.

Similar results were presented by other researchers who studied the effect of deficient irrigation regimes on densely planted olive trees of the Arbequina variety. More specifically, these scientists claim that in conditions of moderate intensity of water stress, the amount of olive oil produced by the olive trees that underwent the above treatment increased significantly, declaring that the reason this phenomenon occurs is still unknown. Another important finding derived from the same scientists team is that the lack of irrigation of the olive trees generally accelerated the ripening of olive fruits, making it possible to harvest the olives early, thus avoiding their collection in late autumn, where they may appear in autumn.

Additionally, in Cordovil olive trees, it was observed that the productive potential of these trees decreased more sharply in years of reduced production, in cases where they were either irrigated only at critical stages of olive growth, or are not irrigated. However, the olive trees that were irrigated with an amount of water equal to 60% of the soil water capacity showed the highest production of olive oil in a period of 2 years compared to all other interventions.

In another variety of olive trees (Chemlali), some of which were irrigated with saline water, it was also observed that irrigation of these olive trees showed similar results to those mentioned above, in terms of reducing the oil content of the fruits and increasing the olive fruits produced. In addition, in trees of the same variety that were not irrigated, it was observed that their fruits showed the highest oil content throughout the experiments. Another interesting finding from the same research is that the composition of the olives may also be significantly affected by rainfall before the harvest season.

Also, the distribution of irrigation affected, in addition to the amount of olive oil produced and its various organoleptic characteristics. It has been observed that in Cordovil olive trees, the olive oil that had the best organoleptic characteristics derived from olive trees that were watered only at critical stages of olive tree growth (before flowering, at the beginning of the hardening period of the core) shortly before harvest.

Weather conditions

Weather conditions, as is well known, affect both plant growth and productivity. For example, scientists searched about the efficiency of olive tree varieties in semi-mountainous areas located on places in the Mediterranean climate zone. In these conditions it has been observed that the production of olives and olive oil was influenced by both the variety and the year in which the trees are located (productive or not). Also, the production of olive fruits and olive oil was more strongly associated with the number of fruits, rather than their oil content. Therefore, scientists recommend the use of varieties of olive trees that produce a large number of olives and at the same time are characterized by high oil content.

Pruning

In olive trees, the type of pruning that needs to be applied depends on many and varied factors. Moreover, scientific studies have been carried out, which refer to mechanical and manual practices of pruning olive trees where these are densely established in places located on the Mediterranean climate zone. More specifically, scientists report that the effects of pruning interventions on olive production are related to the variety of cultivated olive trees and possibly to their vigorousness. Also, in some varieties that were well adapted to the current climatic conditions, the amount of biomass produced due to pruning did not necessarily affect the amount of olives produced per tree.

Similar experiments conducted in Latin America reveal that in Arbequina olive trees irrigated with enough water to meet their needs, the reference year and the severity of the pruning affected the oil content of the fruit, as well as the dry weight of each fruit separately. In addition, the factors affecting the production of olives and olive oil were also influenced by the season when the pruning was carried out, since in the experimental plots that were pruned in the winter (removal of 75 cm from the perimeter of the tree), the production of olives and olive oil appeared increased. compared to other treatments. However, strict pruning of olive trees during the summer, according to the same scientists is not recommended, due to the reduced productivity of olive trees.

Soil amendments

It is well known that both the composition of the soil and the addition of organic matter to it affect the efficiency of the cultivated species. It has been shown that in olive trees of the Chemlali variety in the treatment concerning the addition of composted materials in combination with the supply of saline irrigation water, was observed increased olive oil production, as well as the ratio of flesh to core in the fruits increased compared to other treatments.

In contrast, studies concerning the effect on addition of organic by-products (including the addition of sheep manure and the addition of municipal solid waste) in olive tree productivity found that statistically significant differences in olive production occurred only in the last year of the experiment, in experimental plots where sheep and those where green manure vermicompost was added.

Discussion

From all the above, it is clearly understood that the yield of olive trees depends mainly on the characteristics of the variety cultivated. However, their productivity is affected both by abiotic factors (climatic conditions, soil) and by the extent of various cultivation cares carried out. More specifically, research aimed at finding the water needs of olive trees – which are related either to its quantity or to its distribution during the year in critical phases of olive fruit growth – can provide valuable information on production of olives and olive oil. Similarly, pruning season combined with pruning rigidity strongly affects the productivity of olive trees. Finally, another important factor that affects the production of olive trees is the composition of the added by-products, rich in organic matter, as they affect the amount of olives produced and consequently the amount of olive oil produced.

References

Albarracín,V, Hall,A.J., Searles,P.S., Rousseaux,M.C. (2017), Responses of vegetative growth and fruit yield to winter and summer mechanical pruning in olive trees, Scientia Horticulturae, 225, 185-194. http://dx.doi.org/10.1016/j.scienta.2017.07.005

Centeno,A., Hueso,A., Gómez-del-Campo,M. (2019), Long-term evaluation of growth and production of olive cultivars in super high-density orchard under cold-weather conditions, Scientia Horticulturae, 257, 108657. https://doi.org/10.1016/j.scienta.2019.108657

Chehab,H., Tekaya,M., Hajlaoui,H., Abdelhamid,S., Gouiaa,M., Sfina,H., Chihaoui,B., Boujnah,D., Mechri,B. (2020), Complementary irrigation with saline water and soil organic amendments modified soil salinity, leaf Na +, productivity and oil phenols of olive trees (cv. Chemlali) grown under semiarid conditions, Agricultural Water Management, 237, 106183. https://doi.org/10.1016/j.agwat.2020.106183

Ghrab,M., Gargouri,K., Bentaher,H., Chartzoulakis,K., Ayadi,M., Ben Mimoun,M., Moncef Masmoudi,M., Ben Mechlia,N., Psarras,G. (2013), Water relations and yield of olive tree (cv.Chemlali) in response to partial root-zone drying (PRD) irrigation technique and salinity under arid climate, Agricultural Water Management, 123, 1-11. http://dx.doi.org/10.1016/j.agwat.2013.03.007

Gucci,R., Caruso,G., Gennai,C., Esposto,S., Urbani,S., Servili,M. (2019), Fruit growth, yield and oil quality changes induced by deficit irrigation at different stages of olive fruit development, Agricultural Water Management, 212, 88-98. https://doi.org/10.1016/j.agwat.2018.08.022

Iniesta,F., Testi,L., Orgaz,F., Villalobos,F.J. (2009), The effects of regulated and continuous deficit irrigation on the water use, growth and yield of olive trees, European Journal of Agronomy, 30, 258-265.
Ramos,A.F., Santos,F.L. (2010), Yield and olive oil characteristics of a low-density orchard (cv. Cordovil) subjected to different irrigation regimes, Agricultural Water Management, 97, 363-373. https://doi.org/10.1016/j.agwat.2009.10.008

Rosecrance,R.C., Krueger,W.H., Milliron,L., Bloese,J., Garcia,C., Mori,B. (2015), Moderate regulated deficit irrigation can increase olive oil yields and decrease tree growth in super high density ‘Arbequina’ olive orchards, Scientia Horticulturae, 190, 75-82. http://dx.doi.org/10.1016/j.scienta.2015.03.045

Roussos,P.A., Gasparatos,D., Kechrologou,K., Katsenos,P., Bouchagier,P. (2017), Impact of organic fertilization on soil properties, plant physiology and yield in two newly planted olive (Olea europaea L.) cultivars under Mediterranean conditions, Scientia Horticulturae, 220, 11-19. http://dx.doi.org/10.1016/j.scienta.2017.03.019

Tejada,M., Benítez,C. (2020), Effects of different organic wastes on soil biochemical properties and yield in an olive grove, Applied Soil Ecology, 146, 103371. https://doi.org/10.1016/j.apsoil.2019.103371

Vivaldi,G.A, Strippoli,G., Pascuzzi,S., Stellacci,A.M., Camposeo,S. (2015), Olive genotypes cultivated in an adult high-density orchard respond differently to canopy restraining by mechanical and manual pruning, Scientia Horticulturae, 192, 391-399. http://dx.doi.org/10.1016/j.scienta.2015.06.004

Wiesman,Z. Chapter 8: Olive-harvesting biotechnologies in: Desert Olive Oil Cultivation: Advanced Biotechnologies (2009), Academic Press. https://doi.org/10.1016/B978-0-12-374257-5.00008-7

Approaches in controlling Verticillium dahliae spread

The impact of Verticillium dahliae existence in crop production

The ascomycete Verticillium dahliae is characterized as a pathogen of great economic importance, because of its detrimental action to healthy plants, in combination of the large number of plant species that become vulnerable to it. More specifically, this fungus is detrimental to the health of almost all dicotyledons tree species, to the point that they may undergo universal wilting.

As mentioned above, the number of plant species affected by the pathogenicity of this fungus is large and in these specires are included plant species of great economic importance, such as olives and other cultivated plant species like cotton and potatoes. Therefore, these losses concern producers directly (reduced quantity and degraded quality of harvested products), but also indirectly, through the possible loss of established plants, especially in arboricultures. Also, the presence of this pathogen is worrying not only in the field, but also in nurseries where propagules are produced and the control of V.dahliae presents difficulties.

Spreading and control measures regarding Verticillium dahliae

The dissemination of V.dahliae takes place mainly through microsclerotia, structures that contribute to its further spread. These microsclerotia become contagious when secretions produced by the roots of host plants are present and reproduce on the dead tissues of the host in the final stages of the fungal biological cycle.
Also, the infectivity of this fungus is related to the anatomical traits of plants, at least as far as concerns tree species. More specifically, the intensity of the appeared symptoms is affected by the ability of plants to isolate and replace parts where they had been infected by the fungus. Therefore, the chances of survival of a tree capable of partitioning and timely repair all infected parts of the woody vascular system (xylem) are increased compared to other plant species, where the isolation and repair of these parts is carried out slowly or not at all.

As it becomes noticeable, the strategies involved in V.dahliae control if is entered in the field by any way, is focused on reducing the number of microsclerotia available to soil. In addition, despite the fact that some cultivation measures reduce their population on soil, their management is still problematic, due to their survival in this for a long time (at least a decade) and due to their survival regardless of host existence, even at great depth.

Due to the above mentioned problems and due to the lack of techniques aimed at healing the infected trees, control of V.dahliae is based on the observance of preventive measures. More specifically, the existing measures include the selection of healthy propagating material, planting of varieties that are resistant or even tolerant to the fungus, varieties that may result from cross-breeding of existing varieties with others from genetic material banks, and even from wild relative species.

In addition, measures focusing on the indirect suppression of further transmission of the pathogen, such as thorough cleaning of agricultural machinery as well as the burn of infected plants or the residues they leave, contribute significantly to reducing the spread of the infection.

Also, although crop rotation is considered by some as a measure to restrict V.dahliae spread is not considered economically viable, as the large number of host plants in combination with the longevity of microsclerotia make its implementation difficult. However, maintaining a history of previously cultivated plant species and species of pathogens that have previously appeared in the field would facilitate the selection of plants or varieties to be cultivated.

As previously mentioned, the control of this pathogen is carried out mainly by taking precautionary measures. However, scientists have focused on eradicating – or even limiting – the transmission of V.dahliae, either through the usage of fungicidal chemicals or through biological control methods, such as the use of biological preparations or composted materials.

Regarding the control of V.dahliae with the use of chemical preparations or in combination with using other methods on parallel, such as solarization, they showed remarkable results. More specifically, the use of prochloraz in combination with the addition of complexes in vitro and field conditions has been shown to be effective, at least in terms of the effectiveness of these substances in vitro conditions.

Also, in the past, phosphorous fungicides with systemic action were used, which are considered environmentally friendly, due to their decomposition through physiological processes. However, although these preparations have a more generic fungicidal action, in the case of V.dahliae they inhibited its growth to a considerable extent and therefore the conclusion is that they acted as fungistatics and not as fungicides in vitro.

In addition to the control measures taken against the pathogen using chemical substances, the use of biological preparations is being investigated in the context of organic agriculture. More specifically, in the case of insect pathogenic fungi solutions tested in vitro, it was observed that they not only suppress the growth of V.dahliae hyphaes, but also significantly inhibit the formation of microsclerotia and consequently the further spread of the pathogen. This effect is probably due to the production of secondary metabolites, which may suppress the growth of the pathogen (and several other pathogens). In addition, scientists claim that the effectiveness of these fungi, although affected by pH – a phenomenon observed in the action of various fungicides – is not affected by relatively high temperatures and ultraviolet radiation.

Finally, alternative ways of controlling V.dahliae may potentially be the colonization of fungi and bacteria competing with the fungus in seedlings, as well as the use of composted materials, which is mentioned below.

Regarding the biological control of this pathogen, the addition of composted materials to the soil, either individually or in combination with using various other materials, is also included. More specifically, remarkable results have been observed in terms of long-term control of the pathogen in sandy soils, when interventions involve the addition of chitin-rich material and/or the incorporation of fresh plant mass into the soil combined with the addition of thick plastic sheet.

In addition, in suppressing the growth of V.dahliae, they have been also used in the past in clay loam soils composted waste from fruit extraction, such as marcs or by-products from dairy production with remarkable – albeit temporary – results in the eradication of V.dahliae.

References

Arici, S.E and Demirtas, A.E (2019) The effectiveness of rhizosphere microorganisms to control Verticillium wilt disease caused by Verticillium dahliae Kleb.in olives. Arabian Journal of Geosciences, 12, 781. https://doi.org/10.1007/s12517-019-4962-3

Borza, T., Peters, R.D., Gao, X., Wang-Pruski, G. (2019) Effects of phosphite on the in vitro growth of Verticillium nonalfalfae and Verticillium dahliae and on their in vivo ability to infect potato plants. Eur J Plant Pathol, 155, 1333-1344. https://doi.org/10.1007/s10658-019-01859-z

Keykhasaber, M., Thomma, B.P.H.J., Hiemstra, J.A. (2018) Verticillium wilt caused by Verticillium dahliae in woody plants with emphasis on olive and shade trees. Eur J Plant Pathol, 150, 21-37.

Korthals, G.W., Thoden, T.C., Van den Berg,W., Visser, J.H.M. (2014) Long-term effects of eight soil health treatments to control plant-parasitic nematodes and Verticillium dahliae in agro-ecosystems. Applied Soil Ecology, 76, 112-123. http://dx.doi.org/10.1016/j.apsoil.2013.12.016

Kurt, S., Dervis. S, Sahinler, S. (2003) Sensitivity of Verticillium dahliae to prochloraz and prochloraz–manganese complex and control of Verticillium wilt of cotton in the field. Crop Protection, 22, 51-55.

López-Escudero, F.J., Mercado-Blanco, J. (2011) Verticillium wilt of olive: a case study to implement an integrated strategy to control a soil-borne pathogen. Plant Soil, 344, 1-50.

Lozano-Tovar, M.D., Garrido-Jurado,I., Quesada-Moraga,E., Raya-Ortega,M.C., Trapero-Casas,A. (2017) Metarhizium brunneum and Beauveria bassiana release secondary metabolites with antagonistic activity against Verticillium dahliae and Phytophthora megasperma olive pathogens. Crop Protection, 100, 186-195. http://dx.doi.org/10.1016/j.cropro.2017.06.026

Romanyà,J., Sancho-Adamson,M., Ortega,D., Isabel Trillas,M. (2019) Early stage effects of Verticillium wilt of olive (WVO) on nutrient use in young olive trees grown in soils amended with compost and mineral fertilisation. Plant Soil, 436, 193-209. https://doi.org/10.1007/s11104-018-03923-9

Tubeileh, A.M., Stephenson,G.T. (2020) Soil amendment by composted plant wastes reduces the Verticillium dahliae abundance and changes soil chemical properties in a bell pepper cropping system. Current Plant Biology, 22, 100148. https://doi.org/10.1016/j.cpb.2020.100148

Tymon, L.S., Morgan, P., Gundersen, B., Inglis, D.A. (2020) Potential of endophytic fungi collected from Cucurbita pepo roots grown under three different agricultural mulches as antagonistic endophytes to Verticillium dahliae in western Washington. Microbiological Research, 240, 126535. https://doi.org/10.1016/j.micres.2020.126535

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Wild Vegetables in everyday life

Wild Vegetables usefulness

The contribution of Wild Vegetables in our everyday life is multibranched. In particular, these plant species are mainly used in our nutrition, as well as medicines in terms of traditional medicine either unprocessed (as cataplasms or powder) or as commercially available medicines.

Furthermore, the usage of Wild Vegetables as medicines is not restricted to humans, but these can also be used in animal breeding. Also, these species can be utilized in agricultural sector either to control soil borne pathogens or in order to hamper fungi development spotted on fruits and vegetables after their harvest. Moreover, wild vegetables contain, like Medicinal and Aromatic Plants bioactive substances and secondary metabolites whose presence is responsible for all above mentioned uses.

Additionally, it is worth mentioning the potential utilization of these species on the development of ecotourism, mainly in areas where used to thrive and consequently bringing to light traditional recipes that were possibly obsolete.

Bond between society and Wild Vegetables

Wild Vegetables held a prominent position, mainly in periods characterized by sociopolitical turbulence. However, despite the attempts aimed to promote these species on gourmet cuisine and recognize them as healthy foodstuffs, these species are still undervalued. This contempt for these species is due to the abandonment of rural activities and generally due to the lacking contact between human and nature.

Nevertheless, this phenomenon has been observed from the Renaissance era – in an era that food scarcity didn’t exist – due to several reasons. One of those was the establishment of the stereotype that wild vegetables were cheap food which only poor people eat. Moreover, the introduction of new cultivated plant species, such as sugar beets had redefined the peoples’ nutritional habits. Furthermore, scarce education about Wild Vegetables fosters the perpetuation of the above mentioned phenomenon.

Factors influencing Wild Vegetable collection

Despite the almost obscure importance of wild vegetable species in our everyday life, there are still people who collect these plants. Referring to the capability of these plant collection, this is influenced by many factors. The most important of them has to do with the accessibility on places where these thrive, as well as the reason that someone collects them.

Moreover, in these factors are included the distance of households from markets which distribute them,even the gender of the head of the household. For example, women prefer gathering wild vegetables, while men prefer other activities that have to do with food gathering, such as hunting or fishing. Last but not least, the difficulty in their cleaning and consequently in their preparation on meals has a significant impact on the likelihood of collecting them, because nowadays it is difficult to find time cleaning them.

Wild Vegetables as part of Mediterranean Diet

As previously stated, wild vegetables are mainly used for peoples’ nutrition. However, it is important to focus on Mediterranean Diet, because of the fact that these plants are eaten together with extra virgin olive oil, which is believed to be the basis of this nutritional system.

These plant species are characterized by high nutritional value, because these contain antioxidants in significant amounts as compared to other consumption sources, such as wine. Also, it has been proved that when Cretan Diet, a nutritional model based on the principles of Mediterranean Diet is adopted by someone, has less possibilities to suffer from cardiovascular diseases.

Proposals for promoting Wild Vegetable importance in everyday life

While wild vegetables remain almost unnoticed by people, there are several actions to be taken in order to demonstrate the actual importance of these species in our everyday life.

First and foremost, there is the urgent need to inform society about the beneficial uses of wild vegetables by any means (mainly via internet and media). Also, in this attempt can contribute famous chefs or people who have deeper knowledge about these plants than the general public.

Moreover, the production of wild vegetable propagules combined with promotion of their cultivation through financial incentives would make feasible to cultivate these plants more extensively. Last but not least, some species of these plants can be potentially utilized on plant breeding, due to their adaptability on harsh weather conditions.

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Human and Medicinal and Aromatic Plants (MAPs)

Medicinal and Aromatic Plants in everyday life

From the ancient times, Medicinal and Aromatic plants hold a prominent position in people everyday life. In particular, these plants were used in traditional medicine for their diuretic, antihypertensive and even contraceptive properties, causing less side effects on patients.

Nowadays the amount of knowledge and usages known for Medicinal and Aromatic plants have been significantly increased due to the detection of bioactive compounds contained, such as flavonoids and secondary metabolites. These metabolites are extremely important – mainly concerning pharmaceutical industry – because of their contribution to drug development those which either derive solely from plants or drugs having more complicated synthesis (synthetic medicines), whose active compound derives from a molecule similar in composition to those extracted from plant tissues. Furthermore, as for essential oils that can be extracted from Medicinal and Aromatic plants, these can be potentially used not only individually but in combination with other substances thus enhancing their efficiency.

As for human nutrition, Medicinal and Aromatic plants can be used as spices on dishes, as tisanes, as well as diet supplements. Furthermore, these can be potentially used in food industry either to improve nutritional value of some foods or as natural food preservation additives.

Medicinal and Aromatic Plants and biodiversity

Unfortunately, many Medicinal and Aromatic plant species are still on the verge of extinction, especially those which are commercially exploitated. This phenomenon continues to exist due to anthropogenic actions detrimental to the environment, such as forest areas degradation and the rapid development of agricultural practices. Moreover, Medicinal and Aromatic plants collection in a wrong manner (plants uprooting) is a habit that contributes to the gradual extinction of these species. Also, the extent of this phenomenon is affected by abiotic factors, such as the annual rainfall distribution which is crucial for plants survival.

Proposals for Medicinal and Aromatic Plants conservation

As previously stated, despite the fact that Medicinal and Aromatic plants exploitation continues, there are ways that society can eradicate -or at least limit- the extent of this continual situation, mainly protecting them by any means.
Specifically, in these means are included the cultivation of Medicinal and Aromatic plants more extensively in places away from their biotopes that thrive, as well as the erection of botanical gardens accessible to the general public in order the collection of these plants can be feasible limiting degradation of these biotopes that plants prosper. Also, Medicinal and Aromatic plants can be potentially cultivated by farmers, because of the high income that offer to them, combined with their potential use in crop rotation systems.

Furthermore, there have been recorded many scientific attempts focused on the preservation of Medicinal and Aromatic plants, mainly using tissue culture techniques especially in plant species showing great financial interest. It is interesting to note the potential usefulness of gene bank existence due to the capability to preserve plant propagules in case these plants species extinct.

Beyond all those ways of Medicinal and Aromatic plant conservation mentioned above, there are more ways to protect these plants indirectly, by informing general public either by professionals that are familiar with the usage of Medicinal and Aromatic plants in alternative therapeutic methods or by media.

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