An understanding of the mechanisms that determine plant response to reduced water availability is essential to improve water-use efficiency (WUE) of stone fruit crops. The physiological, biochemical and molecular drought responses of four Prunus rootstocks (GF 677, Cadaman, ROOTPAC 20 and ROOTPAC(®) R) budded with 'Catherina' peach cultivar were studied. Trees were grown in 15-l containers and subjected to a progressive water stress for 26 days, monitoring soil moisture content by time domain reflectometry. Photosynthetic and gas exchange parameters were determined. Root and leaf soluble sugars and proline content were also measured. At the end of the experiment, stressed plants showed lower net photosynthesis rate, stomatal conductance and transpiration rate, and higher intrinsic leaf WUE (AN/gs). Soluble sugars and proline concentration changes were observed, in both root and leaf tissues, especially in an advanced state of stress. The accumulation of proline in roots and leaves with drought stress was related to the decrease in osmotic potential and increase in WUE, whereas the accumulation of sorbitol in leaves, raffinose in roots and proline in both tissues was related only to the increase in the WUE. Owing to the putative role of raffinose and proline as antioxidants and their low concentration, they could be ameliorating deleterious effects of drought-induced oxidative stress by protecting membranes and enzymes rather than acting as active osmolytes. Higher expression of P5SC gene in roots was also consistent with proline accumulation in the tolerant genotype GF 677. These results indicate that accumulation of sorbitol, raffinose and proline in different tissues and/or the increase in P5SC expression could be used as markers of drought tolerance in peach cultivars grafted on Prunus rootstocks.

We previously identified a cluster of d ormancy-a ssociated M ADS-box transcription factors (DAM genes) in peach [Prunus persica (L.) Batsch] as potential candidates for control of the non-dormant phenotype observed in the evg mutant. Of these genes, DAM3, DAM5 and DAM6 were winter expressed, suggesting a role for these genes during endodormancy. We used peach cultivars with contrasting chilling requirements (CR) for bud break to observe the expression of DAM3, DAM5 and DAM6 in response to chilling accumulation in the field and controlled environments. Vegetative terminal and floral buds were sampled weekly from field grown 'Contender' (1050 h CR), 'Rubyprince' (850 h CR) and 'Springprince' (650 h CR) peach cultivars through winter 2008-2009. Flower and vegetative terminal bud break potential was evaluated at each sampling by forcing cuttings in a growth-permissive environment. We also measured vegetative terminal bud break and DAM gene expression in potted 'Contender' and 'Peen-To' (450 h CR) trees under controlled-environment cold exposure. DAM3, DAM5 and DAM6 are all suppressed by exposure to chilling temperatures in the field and in controlled conditions. Expression of DAM5 and DAM6 are higher in high chill cultivars prior to chilling accumulation and their expression level reaches a minimum in each cultivar coincident with acquisition of bud break competence. Expression levels of DAM5 and DAM6 in vegetative tips in controlled environment conditions were negatively correlated with the time required for bud break in forcing conditions. The expression patterns of DAM5 and DAM6 are consistent with a role as quantitative repressors of bud break.

Background: Dormancy associated MADS-box (DAM) genes are candidates for the regulation of growth cessation and terminal bud formation in peach. These genes are not expressed in the peach mutant evergrowing, which fails to cease growth and enter dormancy under dormancy-inducing conditions. We analyzed the phylogenetic relationships among and the rates and patterns of molecular evolution within DAM genes in the phylogenetic context of the MADS-box gene family.

Epidemiological studies suggest that consumption of fruit rich in phenolic compounds is associated with health-protective effects due to their antioxidant properties. For these reasons quality evaluation has become an important issue in fruit industry and in breeding programs. Phytochemical traits such as total phenolics, flavonoids, anthocyanins, L-ascorbic acid, sugar content and relative antioxidant capacity (RAC) were analyzed over four years in flesh fruit of an F1 population “Venus” × “Big Top” nectarines. Other traits such as harvesting date, yield, fruit weight, firmness, soluble solids concentration (SSC), pH, titratable acidity (TA) and ripening index (RI) were also determined in the progeny. Results showed high variability among genotypes for all analyzed traits. Total phenolics and flavonoids showed significant positive correlations with RAC implying that both are important antioxidant bioactive compounds in peaches. We found genotypes with enhanced antioxidant capacity and a better performance than progenitors, and in consequence the best marketability.

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BackgroundIn many tree species the perception of short days (SD) can trigger growth cessation, dormancy entrance, and the establishment of a chilling requirement for bud break. The molecular mechanisms connecting photoperiod perception, growth cessation and dormancy entrance in perennials are not clearly understood. The peach [Prunus persica (L.) Batsch] evergrowing (evg) mutant fails to cease growth and therefore cannot enter dormancy under SD. We used the evg mutant to filter gene expression associated with growth cessation after exposure to SD. Wild-type and evg plants were grown under controlled conditions of long days (16 h/8 h) followed by transfer to SD (8 h/16 h) for eight weeks. Apical tissues were sampled at zero, one, two, four, and eight weeks of SD and suppression subtractive hybridization was performed between genotypes at the same time points.ResultsWe identified 23 up-regulated genes in the wild-type with respect to the mutant during SD exposure. We used quantitative real-time PCR to verify the expression of the differentially expressed genes in wild-type tissues following the transition to SD treatment. Three general expression patterns were evident: one group of genes decreased at the time of growth cessation (after 2 weeks in SD), another that increased immediately after the SD exposure and then remained steady, and another that increased throughout SD exposure.ConclusionsThe use of the dormancy-incapable mutant evg has allowed us to reduce the number of genes typically detected by differential display techniques for SD experiments. These genes are candidates for involvement in the signalling pathway leading from photoperiod perception to growth cessation and dormancy entrance and will be the target of future investigations.

In this study, the field performance of Adara, CAB 6P, Gisela 5, MaxMa 14, Saint Lucie GF 64 (SL 64), Saint Lucie GF 405 (SL 405), and Tabel-Edabriz rootstocks, grafted with two sweet cherry cultivars ('Stark Hardy Giant' and 'Van', Prunus avium L.), were compared after seven years of planting on a calcareous clay-loam soil. The leaf and shoot mineral elements analysed were N, P, K, Ca, Mg, Fe, Mn, Zn, Na and Cu. In the case of both cultivars, tree vigour and cumulative yield were highest on Adara, whereas yield efficiency was greater on Gisela 5. All rootstocks induced low leaf

17The field performance of fifteen peach and plum based rootstocks of different vigour 18 (Adesoto, Evrica, Garnem, GF 677, HM-2, Krymsk