Jean Giannettini

Genetic relationships between cultivated and wild olives of Corsica and Sardinia using RAPD markers

In order to ensure the genetic diversity of the Olea europaea complex,it is necessary to characterize the cultivated varieties and the wildpopulations. In the present study, we focused on the olives growing on twoMediterranean islands, Corsica and Sardinia. On these two islands, there areolives with many denominations, as well as forests of oleasters. Here, it wasproposed to determine the relationships among cultivated and wild olives.Some Italian denominations were studied in addition to assess the influenceof the mainland on the two islands in this respect.The 59 RAPD markers obtained showed the existence of manysynonymous, and homonymous. A dendrogram was constructed using theUPGMA method and a FCA was carried out. The results of these twoanalyses showed the existence of a genetic divergence between the oleastersand the cultivated varieties. They suggest that some of the Corsicanvarieties were probably selected from local wild forms, contrary to theSardinian varieties. They also show that there are feral forms growing onboth islands, which result from hybridization between oleasters andvarieties.

Comparison of photosynthesis and antioxidant performance of several Citrus and Fortunella species (Rutaceae) under natural chilling stress

Citrus plants originate from southeastern Asia, in a large area with various climates characterized by a broad range of temperatures. Some species have been diversified in temperate climates, others in subtropical climates. Temperature is assumed to be a key factor in citrus species adaptation and diversification of basic cellular functions. In a field experiment, the tolerance of the three fundamental Citrus species C. medica L., C. reticulata Blanco and C. maxima (Burm.) Merr., and Fortunella japonica (Thunb.) Swing. to photooxidative stress caused by seasonal climatic changes was evaluated on adult trees by measuring net photosynthesis (Pnet), stomatal conductance (Gs), maximum photosynthesis (Pmax) and chlorophyll fluorescence (Fv/Fm). In addition, seasonal changes in oxidative status, antioxidant enzymes (superoxide dismutase, catalase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase) and antioxidant metabolites (ascorbate and glutathione) were monitored. Mandarin and pummelo appeared to be the most tolerant, showing the lowest down-regulation of photosynthetic parameters, and the lowest accumulation of oxidized compounds associated with efficiency of their antioxidant system. Kumquat showed intermediate behaviour, with a large diminution of photosynthetic parameters and marked accumulation of hydrogen peroxide, whereas the malondialdehyde content remained low, with a strong induction of glutathione synthesis. Finally, citron appeared to be the most sensitive genotype with a marked decrease in photosynthetic performance, the largest accumulation of oxidative parameters, insufficient induction of antioxidant enzymes and down-regulation of ascorbate and glutathione synthesis.

Tetraploid Carrizo citrange rootstock (Citrus sinensis Osb.*Poncirus trifoliata L. Raf.) enhances natural chilling stress tolerance of common clementine (Citrus clementina Hort. ex Tan)

Low temperatures can disturb the development, growth and geographic distribution of plants, particularly cold-sensitive plants in the Mediterranean area, where temperatures can reach seasonally low levels. In citrus crops, scion/rootstock combinations are used to improve fruit production and quality, and increase tolerance to biotic and abiotic stresses. In the last decade, several studies have shown that tetraploid citrus seedlings or rootstocks are more tolerant to abiotic stress than their respective diploid. The objective of this study was to test whether the use of tetraploid rootstocks can improve the chilling tolerance of the scion. We compared physiological and biochemical responses to low seasonal temperatures of common Clementine (Citrus sinensis Osb.×Poncirus trifoliata L. Raf.) grafted on diploid and tetraploid Carrizo citrange rootstocks, named C/2xCC and C/4xCC, respectively. During the coldest months, C/4xCC showed a smaller decrease in net photosynthesis (Pn), stomatal conductance (Gs), chlorophyll fluorescence (Fv/Fm), and starch levels, and lower levels of malondialdehyde and electrolyte leakage than C/2xCC. Specific activities of catalase (CAT), ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) were higher in C/4xCC during the cold period, whereas chlorophyll, proline, ascorbate and hydrogen peroxide (H2O2) levels and superoxide dismutase (SOD) activity did not vary significantly between C/4xCC and C/2xCC throughout the study period. Taken together, these results demonstrate that tetraploid Carrizo citrange rootstock improves the chilling tolerance of common clementine (scion) thanks to a part of the antioxidant system.

Short- and long-term effects of carbohydrate limitation on sugar and organic acid accumulation during mandarin fruit growth

BACKGROUND The physiological roles of organic acids in fruit cells are not fully understood, especially in citrus, whereas the decline in titratable acidity during ripening shown by many citrus fruits is due to the utilization of citric acid. We induced carbohydrate depletion by removing source leaves at two key periods in mandarin development (early and full citric acid accumulation). Then, we assessed the resulting changes in the short term (within 48 h) and long term (several weeks until ripening). RESULTS Control mature fruits were characterized by elevated fresh weight, large diameters and high quantities of malic acid, citric acid and sucrose. At the same stage, fruits subjected to early or late defoliation had higher glucose, fructose, citric acid concentrations and lower sucrose concentrations. They differed only in their malic acid concentrations, which were higher in early defoliation fruits and similar in late defoliation fruits when compared to control fruits. Finally, fruits subjected to late defoliation were characterized by high proline and γ-aminobutyric acid concentrations, and low fructose and glucose concentrations. CONCLUSION We have shown that short- and long-term carbohydrate limitation modifies sugar and organic acid metabolism during mandarin fruit growth.

Effect of chronic arsenic exposure under environmental conditions on bioaccumulation, oxidative stress, and antioxidant enzymatic defenses in wild trout Salmo trutta (Pisces, Teleostei)

The present study evaluates the relation between chronic arsenic (As) exposure in the natural distribution area of wild brown trout (Salmo trutta), oxidative stress and antioxidant enzymatic defenses. Two rivers of the same watershed were evaluated to highlight the correlation between As accumulation and the resulting stress: (i) the Presa River, which has high chronic As levels (2281.66 µg/L) due to past mining activity, and (ii) the Bravona River (control river). This metalloid was measured in main fish tissues (gills, kidney, liver, muscle, gonads and fins) and water. As organotropism in S. trutta was kidney > liver > gill > fin > gonad > muscle. The HepatoSomatic Index (HSI) and somatic condition (CF) were used to compare fish population conditions from both sites. Arsenic can be absorbed by the gills and can induce oxidative stress and disturb antioxidant defenses. The aim of this study was to evaluate oxidative stress response by measuring malondialdehyde (MDA) content, as a marker of lipid peroxidation, and antioxidant enzymatic defenses (Superoxide dismutase (SOD), catalase CAT, glutathione peroxidase (GPx) and glutathione S-transferase (GST)), in the main tissues of control and exposed trout. The highest MDA content was found in the kidney and liver of exposed trout. SOD and CAT activities in exposed livers and kidneys were considerably increased while a significant rise of GPx activity was observed only in the liver. GST activity was found to be significantly induced in the liver of exposed trout. The results demonstrate that arsenic bioaccumulation can induce lipid peroxidation and substantial modifications in antioxidant enzymatic defenses in main wild trout tissues.

Biochemical characterization of the primary metabolism and antioxidant defense systems of acidic and acidless citrus genotypes during the major stages of fruit growth

Fruits are consumed not just for their taste but also for their nutritional value. The major primary metabolites in fruit are sugars and acids, whose contents change during fruit growth and determine ultimate fruit quality. Fruits are also a source of antioxidant metabolites, which are important to human health due to their role in reducing risk of cancer and cardiovascular diseases. Antioxidants are equally important in the plant as they help fight against oxidative stress. Here, we investigated the consequences of changes in the primary metabolism in acidic and acidless citrus genotypes during the major stages of fruit growth on the expression of antioxidant enzymes and the markers of cellular oxidation (hydrogen peroxide, malondialdehyde) in acidless (Iaffaoui orange and sweet lemon) and acidic (Salustiana orange and Villafranca lemon) citrus fruits. Glucose and fructose were the major sugars in the acidless lemon. Sucrose was the major sugar in the acidic lemon. Oranges shared a balance of glucose, fructose, and sucrose. Malic and citric acid concentrations were higher in acidic lemons than acidless fruits. Acidic genotypes had higher hydrogen peroxide concentrations than acidless genotypes, whereas MDA concentrations were higher in oranges than in lemons. Specific activities of ascorbate peroxidase, catalase, superoxide dismutase, and dehydroascorbate reductase were on the whole higher in acidic than acidless fruits. Principal component analysis revealed between-genotype divergence in antioxidant system, giving three groups: acidic lemons, acidless lemons, and oranges.

Somatic hybridization between diploid Poncirus and Citrus improves natural chilling and light stress tolerances compared with equivalent doubled-diploid genotypes

Key messageThe genome doubling of the allotetraploid somatic hybrid can confer greater tolerance to cold and light stress than the diploid parents and their respective tetraploid.AbstractAllopolyploids are generally known to display broader adaptation to abiotic stresses than their parental diploid species. In the Mediterranean area, Citrus species are subjected to abiotic constraints such as low temperature and high radiation. Tetraploids are known to resist these environmental constraints better, and so the use of new tetraploid rootstocks offers an alternative to overcome these threats to crop productivity. The objective of this study was to determine whether the use of an allotetraploid hybrid could provide greater tolerance to cold and light stresses than its diploid parents or respective doubled-diploid parents. We compared cold and light stress responses of the allotetraploid hybrid FlhorAG1 (FL-4x) with those of its diploid parents, the willow leaf mandarin (Citrus deliciosa Ten) (WLM-2x) and the Poncirus Pomeroy (Poncirus trifoliata (L.) Raf.) (POP-2x), and their respective doubled-diploids (WLM-4x and POP-4x, respectively) by measuring physiological and biochemical parameters. When subjected to cold and light stress, FL-4x showed lower photoinhibition (Fv/Fm) and less accumulation of oxidative markers (MDA and H2O2) than diploid and doubled-diploid WLM and POP genotypes. This was correlated with a greater increase for FL-4x in some antioxidant activities during cold stress (SOD, APX and GR) and light stress (SOD, APX and MDHAR mainly). Overall, our results suggest that greater antioxidant capability in FL-4x should make this allotetraploid hybrid more tolerant to low temperatures than the two WLM genotypes, and more tolerant to light stress than the two WLM and POP genotypes.