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

TreesInternational audienceCitrus 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

Physiological and biochemical response to photooxidative stress of the fundamental citrus species

International audienceDespite the economic importance of citrus, insights on the genetic response to stress are scarce. The aim of the present study was to compare fundamental citrus species for their response to photooxidative stress. The experiment was conducted under orchard conditions on three fundamental citrus species C. medica L., C. reticulata Blanco and C. maxima (Burm.) Merr., and on Fortunella japonica (Thunb.) Swing. We examined their respective net photosynthesis (Pnet), stomatal conductance (Gs) and chlorophyll fluorescence (Fv/Fm) on sun-acclimated leaves and shade-acclimated leaves returned under natural sunlight irradiance. To compare the respective response mechanism, we analyzed changes in oxidative status (hydrogen peroxide (H2O2) and malondialdehyde (MDA)), reactive oxygen species (ROS)-scavenging enzymes (superoxide dismutase (SOD), catalase, ascorbate peroxidase), recycling enzymes (monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase) and antioxidant metabolites (ascorbate and glutathione). Kumquat and pummelo exposed lower down-regulation and full recovery of photosynthetic parameters, lower accumulation of oxidized compounds associated with greater production of reduced glutathione (Gsh) and enhanced activity of the three ROS scavenging enzymes, especially SOD. Citron and mandarin showed a marked decrease and incomplete recovery in photosynthetic performance, mainly in Pnet and Fv/Fm, larger accumulation of oxidative parameters, slighter induction of antioxidant enzymes and down-regulation of reduced ascorbate (Asa) and Gsh synthesis. These results suggest that kumquat and pummelo have a greater tolerance to photooxidative stress than citron and mandarin

Nutrient Deficiency Tolerance in Citrus Is Dependent on Genotype or Ploidy Level

Plants require essential minerals for their growth and development that are mainly acquired from soil by their roots. Nutrient deficiency is an environmental stress that can seriously affect fruit production and quality. In citrus crops, rootstock/scion combinations are frequently employed to enhance tolerance to various abiotic stresses. These tolerances can be improved in doubled diploid genotypes. The aim of this work was to compare the impact of nutrient deficiency on the physiological and biochemical response of diploid (2x) and doubled diploid (4x) citrus seedlings: Volkamer lemon, Trifoliate orange × Cleopatra mandarin hybrid, Carrizo citrange, Citrumelo 4475. Flhorag1 (Poncirus trifoliata + and willow leaf mandarin), an allotetraploid somatic hybrid, was also included in this study. Our results showed that depending on the genotype, macronutrient and micronutrient deficiency affected certain physiological traits and oxidative metabolism differently. Tetraploid genotypes, mainly Flhorag1 and Citrumelo 4475, appeared resistant compared to the other genotypes as indicated by the lesser decrease in photosynthetic parameters (Pnet, Fv/Fm, and Gs) and the lower accumulation of oxidative markers (MDA and H2O2) in roots and leaves, especially after long-term nutrient deficiency. Their higher tolerance to nutrient deficiency could be explained by better activation of their antioxidant system. For the other genotypes, tetraploidization did not induce greater tolerance to nutrient deficiency

Caractérisation physiologique et biochimique de la tolérance au stress photooxydatif chez les espèces ancestrales d'agrumes

Le groupe des agrumes vrais est composé de trois principaux genres : Poncirus, Fortunella et Citrus. Ce dernier est constitué d une multitude d espèces dont trois seulement sont à l origine de cette importante diversité : le cédratier, le mandarinier et le pamplemoussier. Chacune de ces espèces est originaire de zones distinctes d Asie du Sud-est dans lesquelles les conditions climatiques ne sont pas les mêmes. L objectif de cette étude est d évaluer le comportement d un génotype de chacune des trois espèces ancestrales et celui d un génotype du genre Fortunella (kumquat) en réponse à deux types de stress photooxydatif, l un engendré par un froid naturel et l autre par une variation d intensité lumineuse. Ces génotypes ont été comparés au niveau physiologique, en déterminant la photosynthèse nette (Pnet), la conductance stomatique (Gs) et la fluorescence chlorophyllienne (Fv/Fm), puis au niveau biochimique en évaluant les activités des enzymes antioxydantes (superoxyde dismutase, catalase ) et les concentrations en peroxyde d hydrogène (H2O2), malondialdéhyde (MDA), ascorbate et glutathion. D après nos résultats, le cédratier présente une sensibilité marquée aux deux catégories de stress en raison des fortes diminutions de ses performances photosynthétiques, des accumulations excessives d H2O2 et MDA et de l activation insuffisante du système antioxydant. A l inverse, le pamplemoussier est tolérant aux deux types de stress au vu des faibles diminutions des paramètres physiologiques, des faibles accumulations d H2O2 et MDA et de l activation importante du système antioxydant. Le mandarinier présente un comportement proche du pamplemoussier aux basses températures et un profil similaire au cédratier en condition de stress lumineux. Enfin, le kumquat montre une réponse intermédiaire entre le cédratier et le mandarinier/pamplemoussier en situation de froid tandis que son comportement est proche du pamplemoussier en situation d excès de lumière.The "true citrus" group is composed of three main genera:Poncirus, Fortunella and Citrus.The latter consists of a multitude of species. Only three of them are responsible for this important diversity: citron, mandarin and pummelo. Each of these species originates from Southeastern Asia in a large area with various climates.The aim of this study is to evaluate the behaviour of a genotype belonging to each of the three fundamental species and that of a genotype from Fortunella genus (kumquat) in response to two kinds of hotooxidative stress.The former is caused by a natural chilling period and the latter by a change in light intensity.These genotypes were first compared at the physiological level by determining net photosynthesis (Pnet), stomatal conductance (Gs) and chlorophyll luorescence (Fv/Fm) and then at the biochemical level by assessing the activities of the main antioxidant enzymes (superoxide dismutase, catalase...) and the concentrations of hydrogen peroxide (H2O2), malondialdehyde (MDA), ascorbate and glutathione.According to our results, citron is sensitive to both types of stress with a marked decrease in photosynthetic performances, a large accumulation of H2O2 and MDA and insufficient activation of the antioxidant system. Conversely, pummelo is tolerant to both types of stress, showing the lowest down-regulation of physiological parameters and the lowest accumulation of H2O2 and MDA associated with efficiency of its antioxidant system. Mandarin exhibits a behaviour equivalent to pummelo atlow temperatures and a behaviour similar to citron under light stress. Finally, kumquat shows intermediate response between citron and mandarin/pummelo under chilling stress while its behaviour is close to pummelo under excess light.CORTE-BU (200962101) / SudocSudocFranceF

Study of tolerance to natural chilling stress in triploid citrus: Monitoring of photosynthetic and antioxidant performances

International audienceCONTEXT: Thanks to favorable pedoclimatic conditions, citrus production is extensively developed in Mediteranean area and mostly focused on fresh-fruit market. Nevertheless, it is well established that abiotic stresses, like low temperatures, reduce plant growth, disrupt photosynthesis and the fluidity of membrane cell. Seedlessness is one of the most consumer expectation on the fresh-fruit market. Polyploidy is an alternative developed to improve tolerance to abiotic stresses. However, little is known about the response of triploid citrus to low temperatures. The creation of triploid hybrid citrus is an alternative to develop innovative seedless commercial varieties, which present a greater abiotic stress tolerance.OBJECTIVES: Determine whether the triploidy can enhance tolerance to natural chilling temperatures of hybrid citru

Synthetic Polyploidy in Grafted Crops

International audienceSynthetic polyploids have been extensively studied for breeding in the last decade. However, the use of such genotypes at the agronomical level is still limited. Polyploidization is known to modify certain plant phenotypes, while leaving most of the fundamental characteristics apparently untouched. For this reason, polyploid breeding can be very useful for improving specific traits of crop varieties, such as quality, yield, or environmental adaptation. Nevertheless, the mechanisms that underlie polyploidy-induced novelty remain poorly understood. Ploidy-induced phenotypes might also include some undesired effects that need to be considered. In the case of grafted or composite crops, benefits can be provided both by the rootstock's adaptation to the soil conditions and by the scion's excellent yield and quality. Thus, grafted crops provide an extraordinary opportunity to exploit artificial polyploidy, as the effects can be independently applied and explored at the root and/or scion level, increasing the chances of finding successful combinations. The use of synthetic tetraploid (4x) rootstocks may enhance adaptation to biotic and abiotic stresses in perennial crops such as apple or citrus. However, their use in commercial production is still very limited. Here, we will review the current and prospective use of artificial polyploidy for rootstock and scion improvement and the implications of their combination. The aim is to provide insight into the methods used to generate and select artificial polyploids and their limitations, the effects of polyploidy on crop phenotype (anatomy, function, quality, yield, and adaptation to stresses) and their potential agronomic relevance as scions or rootstocks in the context of climate change

Enhanced Photosynthetic Capacity, Osmotic Adjustment and Antioxidant Defenses Contribute to Improve Tolerance to Moderate Water Deficit and Recovery of Triploid Citrus Genotypes

International audienceCurrently, drought stress is a major issue for crop productivity, and future climate models predict a rise in frequency and severity of drought episodes. Polyploidy has been related to improved tolerance of plants to environmental stresses. In Citrus breeding programs, the use of triploidy is an effective way to produce seedless fruits, one of the greatest consumer expectations. The current study used physiological and biochemical parameters to assess the differential responses to moderate water deficit of 3x genotypes compared to 2x genotypes belonging to the same hybridization. Both parents, the mandarin Fortune and Ellendale tangor, were also included in the experimental design, while the 2x common clementine tree was used as reference. Water deficit affects leaf water status, as well as physiological and detoxification processes. Triploid genotypes showed a better ability to maintain water status through increased proline content and photosynthetic capacity. Moreover, less oxidative damage was associated with stronger antioxidant defenses in triploid genotypes. We also found that triploidy improved the recovery capacity after a water deficit episode

Influence of Rootstock Genotype and Ploidy Level on Common Clementine (Citrus clementina Hort. ex Tan) Tolerance to Nutrient Deficiency

International audienceNutrient deficiency, in particular when this involves a major macronutrient (N, P, and K), is a limiting factor on the performance of plants in their natural habitat and agricultural environment. In the citrus industry, one of the eco-friendliest techniques for improving tolerance to biotic and abiotic stress is based on the grafting of a rootstock and a scion of economic interest. Scion tolerance may be improved by a tetraploid rootstock. The purpose of this study was to highlight if tolerance of a common clementine scion (C) ( Citrus clementina Hort. ex Tan) to nutrient deficiency could be improved by several diploid (2×) and their tetraploid (4×) counterparts citrus genotypes commonly used as rootstocks: Trifoliate orange × Cleopatra mandarin (C/PMC2x and C/PMC4x), Carrizo citrange (C/CC2x and C/CC4x), Citrumelo 4475 (C/CM2x and C/CM4x). The allotetraploid FlhorAG1 (C/FL4x) was also included in the experimental design. The impact of nutrient deficiency on these seven scion/rootstock combinations was evaluated at root and leaf levels by investigating anatomical parameters, photosynthetic properties and oxidative and antioxidant metabolism. Nutrient deficiency affects foliar tissues, physiological parameters and oxidative metabolism in leaves and roots in different ways depending on the rootstock genotype and ploidy level. The best known nutrient deficiency-tolerant common clementine scions were grafted with the doubled diploid Citrumelo 4475 (C/CM4x) and the allotetraploid FlhorAG1 (C/FL4x). These combinations were found to have less foliar damage, fewer changes of photosynthetic processes [leaf net photosynthetic rate ( P net ), stomatal conductance ( g s ), transpiration (E), maximum quantum efficiency of PSII ( F v / F m ), electron transport rate (ETR), ETR/ P net ], and effective quantum yield of PSII [ Y (II)], less malondialdehyde accumulation in leaves and better functional enzymatic and non-enzymatic antioxidant systems. Common clementine scions grafted on other 4× rootstocks did not show better tolerance than those grafted on their 2× counterparts. Chromosome doubling of rootstocks did not systematically improve the tolerance of the common clementine scion to nutrient deficiency

Tetraploid Citrumelo 4475 rootstocks improve diploid common clementine tolerance to long-term nutrient deficiency

International audienceAbstract Nutrient deficiency alters growth and the production of high-quality nutritious food. In Citrus crops, rootstock technologies have become a key tool for enhancing tolerance to abiotic stress. The use of doubled diploid rootstocks can improve adaptation to lower nutrient inputs. This study investigated leaf structure and ultrastructure and physiological and biochemical parameters of diploid common clementine scions (C) grafted on diploid (2x) and doubled diploid (4x) Carrizo citrange (C/CC2x and C/CC4x) and Citrumelo 4475 (C/CM2x and C/CM4x) rootstocks under optimal fertigation and after 7 months of nutrient deficiency. Rootstock ploidy level had no impact on structure but induced changes in the number and/or size of cells and some cell components of 2x common clementine leaves under optimal nutrition. Rootstock ploidy level did not modify gas exchanges in Carrizo citrange but induced a reduction in the leaf net photosynthetic rate in Citrumelo 4475. By assessing foliar damage, changes in photosynthetic processes and malondialdehyde accumulation, we found that C/CM4x were less affected by nutrient deficiency than the other scion/rootstock combinations. Their greater tolerance to nutrient deficiency was probably due to the better performance of the enzyme-based antioxidant system. Nutrient deficiency had similar impacts on C/CC2x and C/CC4x. Tolerance to nutrient deficiency can therefore be improved by rootstock polyploidy but remains dependent on the rootstock genotype