A B S T R A C TEucalyptus genus is the most widely planted hardwood tree, which productivity and development are limited by low water availability. Plant drought tolerance can be managed by adopting strategies, such as the exogenous application of salicylic acid. The main objective of the present study was to assess whether the exogenous foliar salicylic acid application would ameliorate the damages of water deficit on Eucalyptus globulus plants. Plants were watered at 70% (well water) or 15% (water deficit) of field capacity and four concentrations of salicylic acid (0, 0.75, 2.5 and 5.0 mM) were applied. Water potential, total chlorophylls and carotenoids contents, chlorophyll fluorescence parameters, leaf gas exchange, malondialdehyde, total soluble sugars, starch and total phenols contents were measured. The global hormonal content was quantified by ultra-performance liquid chromatography-mass spectrometry and specific local dynamics of indolacetic acid and abcisic acid were detected by immunolocalization in leaves. A multivariate statistical approach was used to get an overview of the plant physiological status. E. globulus water deficit response included growth rate decline associated with reduced in both water potential and leaf gas exchange parameters. Plant water deficit defence strategies led to an increase in total chlorophylls and carotenoids contents, lipid peroxidation, phenols and total soluble sugars. Six from the 18 hormones detected increased in water deficit plants. Exogenous salicylic acid application improved water deficit tolerance of E. globulus by improving water potential with a positive impact in primary metabolism (photosynthetic rate, soluble sugars) but also in secondary metabolism and defence mechanisms (higher total phenols and less lipid peroxidation) in the highest salicylic acid concentrations. Also, changes in endogenous levels of abscisic and salicylic acids, gibberellins 4 and 7, and specific cytokinins were found in water deficit plants with salicylic acid application. Our results indicated that salicylic acid application could be a potential chemical priming strategy to ameliorate water deficit effects on E. globulus plants.

Food security is a pressing global issue. New approaches are required to break through a yield ceiling that has developed in recent years for the major crops. As important as increasing yield potential is the protection of yield from abiotic stresses in an increasingly variable and unpredictable climate. Current strategies to improve yield include conventional breeding, marker-assisted breeding, quantitative trait loci (QTLs), mutagenesis, creation of hybrids, genetic modification (GM), emerging genome-editing technologies, and chemical approaches. A regulatory mechanism amenable to three of these approaches has great promise for large yield improvements. Trehalose 6-phosphate (T6P) synthesized in the low-flux trehalose biosynthetic pathway signals the availability of sucrose in plant cells as part of a whole-plant sucrose homeostatic mechanism. Modifying T6P content by GM, marker-assisted selection, and novel chemistry has improved yield in three major cereals under a range of water availabilities from severe drought through to flooding. Yield improvements have been achieved by altering carbon allocation and how carbon is used. Targeting T6P both temporally and spatially offers great promise for large yield improvements in productive (up to 20%) and marginal environments (up to 120%). This opinion paper highlights this important breakthrough in fundamental science for crop improvement.

Pine pitch canker (PPC), caused by Fusarium circinatum Nirenberg & O’Donnell, represents an important threat to conifer forests worldwide, being associated with significant economic losses. Although essential to develop disease mitigation strategies, little research focused on host susceptibility/resistance mechanisms has been conducted. We aimed to explore the response of a highly susceptible (Pinus radiata) and a relatively resistant (Pinus pinea) species to F. circinatum infection at different stages of infection. Morpho-physiological, hormonal and oxidative stress-related changes were assessed for each pine species and sampling point. Most of the changes found occurred in symptomatic P. radiata, for which an increased susceptibility to photoinhibition was detected together with decreased superoxide dismutase (SOD) activity. Abscisic acid (ABA) catabolism was activated by F. circinatum inoculation in both pine species, leading to the accumulation of the inactive dihydrophaseic acid (DPA) in P. radiata and of the less-active phaseic acid (PA) in P. pinea. Hormones’ confocal analysis revealed that this strategy may be of particular importance at 6 dpi in P. pinea, which together with photosynthesis maintenance to fuel defence mechanism, could in part explain the species resistance to PPC. These results are of great interest for the development of hormone-based breeding strategies or to the use of hormone application as inducers of resistance to F. circinatum infection.

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Eucalyptus globulus Labill. is widely cultivated and used by industry but its productivity is currently restricted by drought events, so research focussing on supporting programs to breed adapted germplasm is needed. In the present work we monitored severity of acute drought stress (7 and 11 days after water withholding) and relief (2h and 3 days after rewatering) by quantifying several biochemical markers of oxidative stress and DNA methylation patterns in leaves. Water withholding imposed a mild oxidative stress as estimated by redox shifts in the major antioxidant pools and increased lipid peroxidation. At the DNA level, global 5-methylcytosine distribution increased over the dehydration period especially in vascular tissue as estimated by immunolocalisation. Using methylation-sensitive RAPD analysis, which discriminates methylation changes occurring in specific DNA sequences, we found a high number of specific demethylation events also taking place. Immunolocalisation indicated a rapid reduction in global DNA methylation 2h after rehydration; however, a large number of de novo methylation events were still detected by methylation-sensitive RAPD. These events were associated with decreased lipid peroxidation and high cellular GSH pools relative to unstressed plants. Our results indicate the parallel induction of redox and complex DNA methylation changes occurring during stress imposition and relief.