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International audience; Characterization of a seemingly new spherical virus isolated from severely affected plum trees in south-western France indicated that its divided genome is composed of two single-stranded, polyadenylated RNAs of approximately 7.4 and 3.7 kb. Its particles are composed of three coat protein subunits of approximately 23, 23.5, and 24.5 kDa. Partial sequencing of the genomic RNAs indicated that this new virus, tentatively named stocky prune virus (StPV), is distantly related to the two sequenced cheraviruses, cherry rasp leaf virus (CRLV) and apple latent spherical virus (ALSV). StPV should be regarded as a new member in the unassigned genus Cheravirus.

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International audience; A novel virus was identified in banana (Musa spp). Analysis of the last 2917 nucleotides of its positive strand genomic RNA showed five open reading frames corresponding, from 5′ to 3′, to a truncated ORF coding for a replication-associated protein, three ORFs coding for a movement-associated triple gene block (TGB) and a capsid protein (CP) gene. This genome organization is similar to that of some members of the Flexiviridae family such as potexviruses and foveaviruses. This virus was named Banana virus X (BVX). Comparative sequence analysis showed that BVX is only distantly related to other members of the Flexiviridae family, in which it appears to define a new genus. BVX produces defective RNAs derived from its genomic RNA by non-homologous recombination. Three distinct pairs of donor/acceptor recombination sites involving short direct nucleotide repeats were characterized, accounting for deletions of 1268, 1358 and 1503 nucleotides. Contrary to the situation encountered for Potexviruses, these recombination sites are located within the TGB1 and CP genes and result in a truncated TGB1 protein.

A polyvalent nested reverse transcription-polymerase chain reaction (RT-PCR) test using degenerate primers containing inosine (polyvalent degenerate oligonucleotides [PDO]) was developed for filamentous fruit tree viruses belonging to the genera Trichovirus, Capillovirus, and Foveavirus. The 362-bp product was amplified from nucleic acid extracts obtained from Prunus and Malus leaf samples. All the viruses targeted were detected, demonstrating the polyvalence of the test. The variability of a collection of Apple chlorotic leaf spot virus isolates was analyzed using the sequence of the PDO RT-PCR amplified cDNAs. The technique was also used to screen stone fruit materials infected with known agents or with virus-like graft-transmissible diseases of unknown etiology. The results obtained further validated the broad specificity of the assay, with positive amplification obtained for uncharacterized or partially characterized viruses associated with cherry and peach disorders. Sequencing the amplified PCR products either directly or after cloning allowed the identification of variants of known agents and the tentative identification of two new agents, a Trichovirus and a Foveavirus. In addition, sequence comparisons demonstrated that the sequence of the targeted region is phylogenetically informative and of predictive taxonomic value.

Prunus davidiana (Carr.), a wild species with poor fruit quality that is related to peach [Prunus persica (L.) Batsch], is used as a source of resistance to pests and diseases in peach breeding programs. Two genotypes of P. davidiana were studied for fruit biochemical composition and compared to three genotypes of P. persica (`Summergrand', `Bailey' and `Pamirskij'), and two P. persica × P. davidiana hybrids. Fruit of P. davidiana clones had higher malic acid, neochlorogenic and cryptochlorogenic acid and lower sucrose concentrations than fruit of all P. persica genotypes, even poor-quality Bailey. Differences in biochemical composition could be related to sensory evaluation. P. persica × P. davidiana hybrids had intermediate values between their parents for neochlorogenic acid concentration. They were similar to the P. persica parent for total soluble sugar, malic and citric acid, amino acid and catechin concentrations, indicating possible rapid progress for fruit quality in a breeding program.

International audience; Analysis of the P1C124 source (associated with the cherry necrotic mottle leaf (CNML) disease) revealed the presence of two different viral agents. The complete nucleotide sequence of one of these agents, P1A, had an overall nucleotide sequence similarity of 83% with a previously sequenced North American isolate of Cherry green ring mottle virus (CGRMV) and should therefore be regarded as an European isolate of CGRMV. Approximately 2 kb of the 5′ end of the genome of the second agent, P1B, were also sequenced and were shown to be 82% homologous with Cherry necrotic rusty mottle virus (CNRMV), another member of the Foveavirus genus. The possible involvement of CGRMV-P1A and of CNRMV-P1B in the etiology of the CNML disease is discussed.

International audience; Peach asteroid spot (PAS) and peach sooty ringspot (PSRS) are two diseases of stone fruit trees of unknown aetiology. The use of a cRNA probe of the newly described Apricot latent virus (ApLV), a tentative member of the Foveavirus genus, indicated the presence of cross-hybridizing agents in PAS isolate LA2 and in PSRS isolates Caserta 12 and Clava J4. Analysis of dsRNA patterns revealed in each case the presence of a major dsRNA band of about 9.6 kbp. The purified dsRNAs were used to obtain cDNA clones for isolates LA2 and Caserta 12. Sequence analysis of a 1.1 kbp cDNA clone from isolate LA2 showed very high homology with the known ApLV sequence, indicating that this isolate represents a closely related variant of ApLV. Sequence analysis of a 3.06 kbp Caserta 12 cDNA clone representing the 3′ region of the genome revealed a genomic organization similar to that reported for other members of the Foveavirus genus, including the triple gene block and a large, 43.6 kDa coat protein. Sequence comparison with the CP gene of ApLV, the only sequenced region so far for this virus, showed an overall homology of 78%. These results indicate that the foveavirus represented by the Caserta 12 isolate of PSRS disease may be regarded as a distant variant of ApLV. The present results indicate that the viral agents associated with peach asteroid spot and peach sooty ringspot diseases might be variants of the recently described ApLV.

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The protein level and regulation of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31, involved in malic acid synthesis) was studied during the fruit development of two grape (Vitis vinifera L.) varieties, ‘Cabernet Sauvignon’ and ‘Gora Chirine’, with berries of normal and low organic acid content, respectively. The protein level and in vitro activity were higher in the low-acid variety than in the normal-acid variety for most stages. In vivo PEPC activity, measured using 14 CO2 labelling, was significantly higher in the low-acid variety than in the normal-acid variety about 1 week before and 1 week after veraison (the day which corresponds to the onset of ripening). However, partitioning into malate was the same for both varieties. Antibodies raised against the N-terminal part of SorghumPEPC recognised the grape berry PEPC, indicating the presence of the consensus phosphorylation site involved in PEPC regulation. PEPC phosphorylation status was estimated by studying sensitivity to pH and malate. Grape berry PEPC appeared more sensitive to low pH and malate during ripening (IC50 malate, 0.2–0.7 mM) compared to during the earlier stages of development (IC50 malate, 1.2–2 mM) for both varieties. Therefore, in the normal-acid variety, PEPC seems to participate in controlling malic acid accumulation but does not seem to control the differences in malic acid concentration observed between the two varieties.

International audience; The synthesis of organic acids was studied during fruit development of two peach (Prunus persica L, Batsch) cultivars, Fantasia and Jalousia, having fruits with high and low organic acid content, respectively. The malate content was higher in cv. Fantasia than in cv, Jalousia at the end of the first rapid growth stage (50 days after bloom [DAB]). Malate and citrate contents,were higher in Fantasia than in Jalousia during the second rapid growth stage (from 100 DAB to maturity). The expression of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31), which is involved in organic acid synthesis, was studied during peach fruit development. PEPC mRNA levels, and protein levels on a total soluble protein basis, peaked at 23 and 108 DAB in Fantasia. In Jalousia, they were very low at 23 DAB and reached levels similar to Fantasia at 108 DAB, For both cultivars, in vitro PEPC activity expressed on a dry weight basis was maximal at 24 DAB, decreased from 24 to 60 DAB, and then remained constant. The activity of peach fruit PEPC appeared extremely sensitive to malate (I-0.5 of 100 mu M for Fantasia and 65 mu M for Jalousia at pH 7.3) and low pH, PEPC may participate in the control of organic acid accumulation during fruit development in the normal-acid fruit of Fantasia, However, mechanisms other than organic acid synthesis might account for the differences in acidity between normal-acid and non-acid peach fruit.

Changes in metabolites were studied during the fruit development of two greenhouse grown peach [Prunus persica (L.) Batsch] cultivars with low acidity (`Jalousia') or normal acidity (`Fantasia'). Both cultivars had the same sucrose concentration in fruit mesocarp at maturity. In the fruit juice, pH was higher and titratable acidity was lower for `Jalousia' than for `Fantasia' from 80 days after bloom to maturity. At four different times during fruit development, in vivo 13C NMR spectroscopy was used to measure the vacuolar pH of fruit mesocarp. At 55 days after bloom, the vacuolar pH of fruit mesocarp was not significantly different between `Jalousia' and `Fantasia', whereas the juice pH was different between cultivars. The three major organic acids in fruit mesocarp were malic, citric, and quinic acids for both cultivars. Citric acid concentrations were similar in both cultivars until ≈85 days after bloom and then became significantly higher in `Fantasia'. A significantly higher concentration in malic acid in `Fantasia' than in `Jalousia' was observed from the end of the first growth phase to maturity. At maturity, `Fantasia' fruit had two and five times more malic and citric acid, respectively, than `Jalousia' fruit. The differences observed between `Jalousia' and `Fantasia' fruit for malic and citric acid concentrations accounted for the difference in titratable acidity. The differences in acid concentration appeared during the plateau between the two rapid growth phases of the fruit, i.e., far before the onset of maturation. The three major amino acids were asparagine, glutamic acid, and proline for both cultivars. Their concentration followed similar patterns in acid and low-acid fruit.

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Sorbitol and sucrose are the two main soluble carbohydrates in mature peach leaves. Both are translocated in the phloem, in peach as in other rosaceous trees. The respective role of these two soluble carbohydrates in the leaf carbon budget, and their phloem loading pathway, remain poorly documented. Though many studies have been carried out on the compartmentation and export of sucrose in sucrose-transporting species, far less is known about sorbitol in species transporting both sucrose and sorbitol. Sorbitol and sucrose concentrations were measured in several tissues and in sap, in 2-month-old peach (Prunus persica L. Batsch) seedlings, i.e. leaf blade, leaf main vein, petiole, xylem sap collected using a pressure bomb, and phloem sap collected by aphid stylets. The sorbitol to sucrose molar ratio depended on the tissue or sap, the highest value (about 7) found in the leaf main vein. Sorbitol concentration in the phloem sap was about 560 mM, whereas that of sucrose was about 140 mM. The lowest sorbitol and sucrose concentrations were observed in xylem sap collected from the shoot. The volume of the leaf apoplast, estimated by infiltration with 3 H-inulin, represented about 17% of the leaf blade water content. This volume was used to calculate a global intracellular concentration for each carbohydrate in the leaf blade. Following these simplifying assumptions, the calculated concentration gradient between the leaf's intracellular compartment and phloem sap is nil for sorbitol and could thus allow for the symplastic loading of the phloem of this alditol. However, infiltration of 14 C-labelled source leaves with 2 mM p-chloromercuribenzenesulfonic acid (PC-MBS), a potent inhibitor of the sucrose carrier responsible for phloem loading in sucrose-transporting plants, had a significant effect on the exudation of both labelled sucrose and sorbitol from the phloem. Therefore, in peach, which is a putative symplastic loader according to minor vein anatomy and sorbitol concentration gradients, apoplastic loading may predominate.

The winegrape cv. Cabernet Sauvignon and the tablegrape cv. Gora Chirine (both Vitis vinifera L.) differ in the acidity of their berry juice. The changes in pH, titratable acidity and the concentration of compounds of the berry juice were measured from 20–30 d before veraison to harvest on plants cultivated in the glasshouse. The difference in acidity between the juice of the two varieties appeared before veraison. At harvest, the berry juice of Gora Chirine had a pH of 5.2 and titratable acidity (TA) of 32 meq/L while that of Cabernet Sauvignon had a pH of 3.2 and TA of 150 meq/L. To evaluate cellular compartmentation in the berry pericarp, vacuolar pH was measured on intact berries at two growth stages, using 13C nuclear magnetic resonance (NMR). Vacuolar pH did not differ significantly between the two cvs. The lower TA of Gora Chirine juice could be attributed to lower concentrations of all three major acids, malic, tartaric and citric, and to a higher concentration of potassium. At veraison, the malic acid concentration in the berry juice of Cabernet Sauvignon was about seven times higher than that of Gora Chirine. The accumulation of hexoses, especially glucose, occurred earlier during the berry growth cycle in Gora Chirine than in Cabernet Sauvignon. The osmotic potential of the Gora Chirine juice, before veraison, was lower than could have been expected because of low acidity. This was due to the compensatory effect of early accumulation of glucose. Amino acid concentration was significantly higher in Gora Chirine than in Cabernet Sauvignon, especially just before veraison. The role of organic acids in berry acidity and osmotic potential, and various metabolic processes that may lead to the difference in organic acid concentration, are discussed.

Changes in phosphoenolpyruvate carboxylase (PEPC) activity were studied during the fruit development of two peach cultivars (Prunus persica (L.) Batsch) with normal (‘Fantasia’) and low (‘Jalousia’) organic acid concentration. PEPC activities were measured in fruit mesocarp at two stages of development, corresponding to malate accumulation and citrate accumulation phases in ‘Fantasia’, respectively. In vitro activity, measured under optimal conditions, was significantly higher in ‘Fantasia’ than in ‘Jalousia’ during the malate accumulation phase but lower during the citrate accumulation phase. In vivo activity was estimated using 14CO2 labelling. The total incorporated radioactivity was higher in ‘Fantasia’ than in ‘Jalousia’ during the malate accumulation phase but lower during the citrate accumulation phase. During the malate accumulation phase, the partitioning of incorporated 14C into malate was significantly reduced in ‘Jalousia’ compared to ‘Fantasia’ after 20 min labelling. During the citrate accumulation phase, 14 C partitioning into malate was not significantly different between varieties, but partitioning into citrate was significantly reduced in ‘Jalousia’ compared to ‘Fantasia’. Therefore, PEPC activity does not seem to be the controlling step for the absence of organic acid accumulation in ‘Jalousia’ fruit. The other metabolic causes of the difference in organic acid accumulation are discussed; these may be connected with vacuolar storage.

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The organoleptic quality of fleshy fruits is in a large part defined by their composition of soluble sugars and organic acids. An F 2 population issuing from a cross between two peach varieties, 'Ferjalou Jalousia', a non-acid peach, and 'Fantasia', an acid nectarine, was analysed over 2 successive years for agronomic characters and for molecular-marker (isoenzymes, RFLPs, RAPDs, IMAs and AFLPs) segregations. Blooming and maturity dates, as well as productivity, were noted for each tree. Four fruits per tree were analysed at maturity for fresh weight, colour, pH, titratable acidity, soluble-solids content (SSC), acid (malic, citric and quinic acids) and sugar (sucrose, glu- cose, fructose, sorbitol) contents. QTLs were detected for all fruit components analysed, except for fruit col- our. The QTLs for nearly all components were present on two linkage groups. For productivity, fresh weight, pH, quinic acid, sucrose and sorbitol content, all the detected QTLs displayed the same e⁄ect as the parental phenotypes. By contrast, for maturity date, titratable acidity, malic and citric acids and fructose, some QTLs displayed the same e⁄ect as the parental phenotypes while others displayed the opposite e⁄ect. The fraction of the total variation in each trait throughout the population explained by the QTLs was very high and reached more than 90% for some characters. For most