Peter A. Roussos

Comparative effects of organic and conventional apple orchard management on soil chemical properties and plant mineral content under Mediterranean climate conditions

The effects of conventional and organic management systems on soil chemical properties and leaf nutrients under Mediterranean conditions were studied over a 2-year period on adjacent commercial apple orchards in Southern Greece. The soil in both orchards was characterised as a clay loam–clay and was uniform in morphological and physical properties. The results indicated no significant differences in soil chemical properties between the different management systems, including soil organic matter (SOM), pH, cation exchange capacity (CEC) and C/N ratio. However, soil samples from the conventional orchard exhibited significantly higher values (p< 0.01) of electrical conductivity (EC) and higher concentrations of K, Ca, Na, Cu and Zn, which were likely the result of chemical fertiliser application. Despite the fact that organic systems promote the accumulation of soil organic matter and fertility over time through the use of organic sources, in our study, the SOM values declined, suggesting that the type and the rate of organic matter input in the organic orchard were insufficient. The leaf nutrients, with the exception of P and Ca, were within the sufficiency range in both management systems. The present findings did not provide evidence of major differences in the leaf macronutrient content between conventionally and organically grown apple trees. Nevertheless, our leaf analysis revealed higher concentrations of Zn in the conventionally grown trees and opposite results for Cu, probably due to the extensive use of copper-containing fungicides in organic orchards in Greece.

Root promoting compounds detected in olive knot extract in high quantities as a response to infection by the bacterium Pseudomonas savastanoi pv. savastanoi

Olive knot crude extract has been found to promote rooting in vitro of Koroneiki olive explants. The analysis of this extract revealed the presence of the naturally occurring auxins indole-3-acetic acid (IAA) and indole-3-acetonitrile (IAN) in high quantities. Both auxins were found in higher amounts in the knots, formed in olive shoots after the infection by the bacterium Pseudomonas savastanoi pv. savastanoi, than in healthy shoots. Further research showed that the knots were rich in phenolic compounds and o-diphenols, as well as that they contained higher amounts of oleuropein (an o-diphenol) and another unidentified compound in contrast to healthy shoots. The analysis of polyamines showed higher concentrations of putrescine in the knots than in the healthy shoots, while it was not possible to detect any traces of spermidine or spermine in the olive knot extract. The results suggested a possible role and collaboration of auxins, phenolic compounds and polyamines, such as putrescine, in the root induction procedure of olive explants in vitro. Furthermore, a possible defense mechanism of olive tree against the bacterium was postulated, through the increased production of possible anticipins, like IAN and the unknown phenolic compound.

The Possible Role of Polyamines to the Recalcitrance of “Kalamata” Olive Leafy Cuttings to Root

The objective of this study was to investigate the role of endogenous polyamines (PAs) (the sum of free plus soluble conjugate plus insoluble bound) on rooting potential of leafy cuttings of an easy, that is,“Arbequina” and a difficult-to-root olive cultivar, that is, “Kalamata”. Subsamples of cuttings were taken for PAs analysis before planting in the mist system and during the early phases of rhizogenesis (EPR). “Arbequina” exhibited higher initial free and total PA content than “Kalamata”. Spermidine (Spd) was the predominant PA observed in both cultivars. A low content of free putrescine (Put) and Spd was found in both cultivars, whereas spermine (Spm) was occasionally detected. “Arbequina” as well as “Kalamata” exhibited the highest free Put and free Spd in summer and Put was the predominant PA among the free PAs. “Arbequina” exhibited the highest individual and total PAs in spring, followed by those in summer and autumn. In contrast, “Kalamata” had the maximum PAs in summer and the lowest in autumn. Changes in the endogenous content of individual and total PAs during the EPR were also observed. Treatment of “Kalamata” cuttings in autumn with both indole-3-butyric acid (IBA) and Put increased rooting compared to IBA alone. Among the PAs administered, Put was the most effective, whereas Spd and Spm failed to promote rooting. PAs, especially in their free form, seem to be involved in the rooting process of olive cuttings; Put application enhanced the rooting response of the difficult-to-root “Kalamata” olive cultivar.

Growth and biochemical responses of jojoba (Simmondsia chinensis (Link) Schneid) explants cultured under mannitol-simulated drought stress in vitro

Jojoba explants were cultured under four levels of mannitol (control plus 50, 100, 250 and 500 mM mannitol)-induced osmotic stress during the proliferation stage in vitro. Explants grown under control condition exhibited the highest growth, while the more severe the stress was, the lower was the growth of explants. Electrolyte leakage, lipid peroxidation, H2O2 content and proline concentration were highest and relative water content lowest under the highest level of osmotic stress. Concentration of phenolic compounds (total phenolic compounds, o-diphenols and flavanols, as well as protocatechuic, vanillic, p-coumaric and ferulic acids and rutin), putrescine and total polyamines decreased with increasing stress level. Mannitol, glucose and pinitol concentrations increased, whereas that of inositol decreased with increasing stress level. Explants were transferred to the rooting stage, separately per stress treatment. Explants grown under stress conditions during the proliferation stage exhibited lower rooting percentage than controls, as the stress became more severe, the lower was the rooting response. Jojoba tolerated osmotic stress to some extent (till 100–250 mM mannitol), exhibiting sufficient growth rate and good rooting response as well as low oxidative damage (based on electrolyte leakage and lipid peroxidation indices).

Growth, Nutrient Status, and Biochemical Changes of Sour Orange Plants Subjected to Sodium Chloride Stress

Sour orange is a valuable citrus rootstock. It is characterized as salt tolerant, based mainly on the mineral content of the leaves and roots under saline environment and to a lesser extent based on any biochemical indices. Therefore, the aim of the present experiment was to study both nutrient content and biochemical changes involved in this rootstocks tolerance. One-year-old sour orange (Citrus aurantium L.) trees growing in 5-L pots were subjected to four levels of sodium chloride salinity stress (control, 40 mM, 80 mM, and 120 mM sodium chloride) for 60 days. At the end of the stress period, plant growth was evaluated by measuring leaf, shoot, and root dry weights. Carbohydrates, chlorophylls, lipid peroxidation, and electrolyte leakage were also determined in leaves. Plant nutrient status was evaluated in leaf, shoot, and root samples, and the soil was also analyzed for nutrient content. Leaf sclerophylly indexes were determined to assess water stress induced by salinity. Leaf dry weight was not significantly affected, whereas shoot and root dry weights decreased with salt stress. Soil electrical conductivity and sodium and chloride concentrations increased with increasing salt concentration, whereas available potassium concentration decreased. Salt stress induced a significant accumulation of sodium and chloride in leaves, shoots, and roots. Potassium and phosphorus concentrations in leaves were enhanced under salt stress, whereas inconsistent changes were detected concerning magnesium, zinc, manganese, and copper concentrations. Sucrose and glucose concentrations were significantly reduced under salt stress while fructose concentration did not exhibit significant changes. Chlorophyll concentration was also reduced under stress. Based on lipid peroxidation and electrolyte leakage indexes, cell membrane integrity was maintained. According to leaf characteristics indexes, leaves’ water stress was negligible, even after 2 months under salt stress. Based on the present results, sour orange accumulated significant amounts of sodium and chloride ions, inducing a reduction of growth, possibly through a reduction of carbon assimilation rate under low chlorophyll content, resulting in reduced carbohydrate concentration in the leaves.

Spatial and temporal distribution of genes involved in polyamine metabolism during tomato fruit development.

Polyamines are organic compounds involved in various biological roles in plants, including cell growth and organ development. In the present study, the expression profile, the accumulation of free polyamines and the transcript localisation of the genes involved in Put metabolism, such as Ornithine decarboxylase (ODC), Arginine decarboxylase (ADC) and copper containing Amine oxidase (CuAO), were examined during Solanum lycopersicum cv. Chiou fruit development and maturation. Moreover, the expression of genes coding for enzymes involved in higher polyamine metabolism, including Spermidine synthase (SPDS), Spermine synthase (SPMS), S-adenosylmethionine decarboxylase (SAMDC) and Polyamine oxidase (PAO), were studied. Most genes participating in PAs biosynthesis and metabolism exhibited an increased accumulation of transcripts at the early stages of fruit development. In contrast, CuAO and SPMS were mostly expressed later, during the development stages of the fruits where a massive increase in fruit volume occurs, while the SPDS1 gene exhibited a rather constant expression with a peak at the red ripe stage. Although Put, Spd and Spm were all exhibited decreasing levels in developing immature fruits, Put levels maxed late during fruit ripening. In contrast to Put both Spd and Spm levels continue to decrease gradually until full ripening. It is worth noticing that in situ RNA-RNA hybridisation is reported for the first time in tomato fruits. The localisation of ADC2, ODC1 and CuAO gene transcripts at tissues such as the locular parenchyma and the vascular bundles fruits, supports the theory that all genes involved in Put biosynthesis and catabolism are mostly expressed in fast growing tissues. The relatively high expression levels of CuAO at the ImG4 stage of fruit development (fruits with a diameter of 3 cm), mature green and breaker stages could possibly be attributed to the implication of polyamines in physiological processes taking place during fruit ripening.

Plum ( Prunus domestica L. and P. salicina Lindl.)

Abstract 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.

Apricot ( Prunus armeniaca L.)

Abstract Apricot is considered to be one of the most delicious temperate fruit’s and is highly appreciated by consumers for its taste and aroma. Fruits characteristic flavor is a complex of sugars, organic acids, phenolic compounds, and volatiles, among others, which differ greatly among cultivars. The main carbohydrate is sucrose followed by glucose and fructose. The antioxidant capacity of apricot is attributed to the presence of phenolic compounds, among which rutin, chlorogenic acid, neochlorogenic acid, and the flavanols catechin and epicatechin are the most abundant, depending on the cultivar. Citric and malic acid are the dominant organic acids. Apricots are rich in β-carotene, giving the fruit its characteristic color. The fine flowery and fruity aroma are composed mainly of volatiles such as ethyl acetate, hexyl acetate, limonene, β-cyclocitral, γ-decalactone, 6-methyl-5-hepten-2-one, 2-hexenal, and hexanal with the various cultivars exhibiting different main volatile compound, to which the cultivar characteristic aroma is attributed.

Orange (Citrus sinensis (L.) Osbeck)

Abstract Of all the citrus species cultivated worldwide, orange ( Citrus sinensis (L.) Osbeck) is the most important. Fruits are characterized by sweet and pleasant taste and a fine aroma that is much appreciated by consumers. Sucrose is the main carbohydrate, and citric acid the dominant organic acid in the juice. It is considered as a rich source of antioxidants, such as ascorbic acid and phenolic compounds (mainly hesperidin and narirutin). It is quite rich in carotenoids (mainly violaxanthin, β-cryptoxanthin, and lutein). In pigmented oranges the color is due to the presence of anthocyanins, except in a few cultivars in which lycopene is the main pigment. The main amino acids found in the juice are proline, serine, and arginine while potassium is the main mineral found in the juice. The fine aroma of the oranges is due to the presence of a number of volatiles, with the most abundant being limonene.