Effect of Rootstock on the Volatile Profile of Mandarins.

Mandarin production has increased in recent years, especially for fresh consumption, due to its ease of peeling, its aroma, and its content of bioactive compounds. In this sense, aromas play a fundamental role in the sensory quality of this fruit. The selection of the appropriate rootstock is crucial for the success of the crop and its quality. Therefore, the objective of this study was to identify the influence of 9 rootstocks ("Carrizo citrange", "Swingle citrumelo CPB 4475", "Macrophylla", "Volkameriana", "Forner-Alcaide 5", "Forner-Alcaide V17", "C-35", "Forner-Alcaide 418", and "Forner-Alcaide 517") on the volatile composition of "Clemenules" mandarin. For this, the volatile compounds of mandarin juice were measured using headspace solid-phase micro-extraction in a gas chromatograph coupled to a mass spectrometer (GC-MS). Seventy-one volatile compounds were identified in the analyzed samples, with limonene being the main compound. The results obtained showed that the rootstock used in the cultivation of mandarins affects the volatile content of the juice, with "Carrizo citrange", "Forner-Alcaide 5", "Forner-Alcaide 418", and "Forner-Alcaide 517" being those that presented the highest concentration.

Comparative transcriptomic analyses of citrus cold-resistant vs. sensitive rootstocks might suggest a relevant role of ABA signaling in triggering cold scion adaption.

BACKGROUND: The citrus genus comprises a number of sensitive tropical and subtropical species to cold stress, which limits global citrus distribution to certain latitudes and causes major economic loss. We used RNA-Seq technology to analyze changes in the transcriptome of Valencia delta seedless orange in response to long-term cold stress grafted on two frequently used citrus rootstocks: Carrizo citrange (CAR), considered one of the most cold-tolerant accessions; C. macrophylla (MAC), a very sensitive one. Our objectives were to identify the genetic mechanism that produce the tolerant or sensitive phenotypes in citrus, as well as to gain insights of the rootstock-scion interactions that induce the cold tolerance or sensitivity in the scion. RESULTS: Plants were kept at 1 ºC for 30 days. Samples were taken at 0, 15 and 30 days. The metabolomic analysis showed a significant increase in the concentration of free sugars and proline, which was higher for the CAR plants. Hormone quantification in roots showed a substantially increased ABA concentration during cold exposure in the CAR roots, which was not observed in MAC. Different approaches were followed to analyze gene expression. During the stress treatment, the 0-15-day comparison yielded the most DEGs. The functional characterization of DEGs showed enrichment in GO terms and KEGG pathways related to abiotic stress responses previously described in plant cold adaption. The DEGs analysis revealed that several key genes promoting cold adaption were up-regulated in the CAR plants, and those repressing it had higher expression levels in the MAC samples. CONCLUSIONS: The metabolomic and transcriptomic study herein performed indicates that the mechanisms activated in plants shortly after cold exposure remain active in the long term. Both the hormone quantification and differential expression analysis suggest that ABA signaling might play a relevant role in promoting the cold hardiness or sensitiveness of Valencia sweet orange grafted onto Carrizo citrange or Macrophylla rootstocks, respectively. Our work provides new insights into the mechanisms by which rootstocks modulate resistance to abiotic stress in the production variety grafted onto them.

Correction: A cross population between D. kaki and D. virginiana shows high variability for saline tolerance and improved salt stress tolerance.

[This corrects the article DOI: 10.1371/journal.pone.0229023.].

A cross population between D. kaki and D. virginiana shows high variability for saline tolerance and improved salt stress tolerance.

Persimmon (Diospyros kaki Thunb.) production is facing important problems related to climate change in the Mediterranean areas. One of them is soil salinization caused by the decrease and change of the rainfall distribution. In this context, there is a need to develop cultivars adapted to the increasingly challenging soil conditions. In this study, a backcross between (D. kaki x D. virginiana) x D. kaki was conducted, to unravel the mechanism involved in salinity tolerance of persimmon. The backcross involved the two species most used as rootstock for persimmon production. Both species are clearly distinct in their level of tolerance to salinity. Variables related to growth, leaf gas exchange, leaf water relations and content of nutrients were significantly affected by saline stress in the backcross population. Water flow regulation appears as a mechanism of salt tolerance in persimmon via differences in water potential and transpiration rate, which reduces ion entrance in the plant. Genetic expression of eight putative orthologous genes involved in different mechanisms leading to salt tolerance was analyzed. Differences in expression levels among populations under saline or control treatment were found. The 'High affinity potassium transporter' (HKT1-like) reduced its expression levels in the roots in all studied populations. Results obtained allowed selection of tolerant rootstocks genotypes and describe the hypothesis about the mechanisms involved in salt tolerance in persimmon that will be useful for breeding salinity tolerant rootstocks.

Rootstock influence on iron uptake responses in Citrus leaves and their regulation under the Fe paradox effect.

BACKGROUND AND AIMS: This work evaluates the regulation of iron uptake responses in Citrus leaves and their involvement in the Fe paradox effect. METHODS: Experiments were performed in field-grown 'Navelina' trees grafted onto two Cleopatra mandarin × Poncirus trifoliata (L.) Raf. hybrids with different Fe-chlorosis symptoms: 030146 (non-chlorotic) and 030122 (chlorotic). RESULTS: Chlorotic leaves were smaller than non-chlorotic ones for both dry weight (DW) and area basis, and exhibited marked photosynthetic state affection, but reduced catalase and peroxidase enzymatic activities. Although both samples had a similar total Fe concentration on DW, it was lower in chlorotic leaves when expressed on an area basis. A similar pattern was observed for the total Fe concentration in the apoplast and cell sap and in active Fe (Fe2+) concentration. FRO2 gene expression and ferric chelate reductase (FC-R) activity were also lower in chlorotic samples, while HA1 and IRT1 were more induced. Despite similar apoplasmic pH, K+/Ca2+ was higher in chlorotic leaves, and both citrate and malate concentrations in total tissue and apoplast fluid were lower. CONCLUSION: (1) The rootstock influences Fe acquisition system in the leaf; (2) the increased sensitivity to Fe-deficiency as revealed by chlorosis and decreased biomass, was correlated with lower FC-R activity and lower organic acid level in leaf cells, which could cause a decreased Fe mobility and trigger other Fe-stress responses in this organ to enhance acidification and Fe uptake inside cells; and (3) the chlorosis paradox phenomenon in citrus likely occurs as a combination of a marked FC-R activity impairment in the leaf and the strong growth inhibition in this organ.