Enhancing Yield and Physiological Performance by Foliar Applications of Chemically Inert Mineral Particles in a Rainfed Vineyard under Mediterranean Conditions

One of the biggest environmental challenges that most of the traditional and modern grape-growing areas are facing is the frequency, severity, and unpredictability of extreme weather events as a result of climate change. Sustainable tools such as chemically inert mineral particles could be a valid alternative for the promotion of environmentally-friendly viticultural techniques to enhance yield, improve physiological processes, and increase tolerance to biotic/abiotic stressors and grape quality. In regard to this concept, the effects of kaolin (KL) and zeolite (ZL) application was tested in the rosé grapevine cultivar Roditis, field-and rainfed, under the Mediterranean conditions of central Greece. In a two-year trial, the whole vine canopy was sprayed with kaolin and zeolite until runoff at a dose of 3% (w/v) twice throughout the growing season; the first at the beginning of veraison and the second one week later; treatment of the untreated control plants was also performed (C). The assimilation rate in morning and midday, the stomatal conductance, and the WUEi of the leaves of the treated and untreated plants were monitored one day after each application and at harvest. During the same time period of the day (i.e., morning and midday) in July, August, and September, the leaf temperature near the fruit zone was also recorded. At harvest, the yield parameters, cluster characteristics, grape composition, and incidence (%) of sunburned and dehydrated berries as well as berries infected by Plasmopara viticola and Lobesia botrana were recorded. The results showed that KL and ZL application decreased leaf temperature during the growing season until harvest compared to the control treatment, which resulted in an improvement in physiological parameters such as net photosynthesis and intrinsic water use efficiency. At harvest, the KL- and ZL-treated vines showed increased yield due to an increasing cluster and berry fresh weight. On the other hand, the KL and ZL application did not affect the sugar concentration and pH of the must and increased the total acidity and decreased the total phenolic compound content, but only in the first year of the experiments. Furthermore, the incidence of sunburn necrosis, dehydrated berries, and infected berries was significantly lower in the treated vines compared to the control vines. These results confirm the promising potential of kaolin and zeolite applications as a stress mitigation strategy during the summer period, with the ability to protect grapevine plants, enhance yield, and maintain or improve fruit quality in rainfed Mediterranean vineyards.

Potassium supply modulates Eucalyptus leaf water-status under PEG-induced osmotic stress: integrating leaf gas exchange, carbon and nitrogen isotopic composition and plant growth

The objective of this study was to quantify the effect of potassium (K) supply on osmotic adjustment and drought avoidance mechanisms of Eucalyptus seedlings growing under short-term water stress. The effects of K supply on plant growth, nutritional status, leaf gas exchange parameters, leaf water potential (Ψw), leaf area (LA), stomatal density (SD), leaf carbon (C) and nitrogen (N) isotopic compositions (δ13C and δ15N ‰) and leaf C/N ratio under polyethylene glycol (PEG)-induced water deficit were measured. Under both control (non-PEG) and osmotic stress (+PEG) conditions, K supply increased plant growth, boosting dry matter yield with decreased C/N leaf ratio and δ15N ‰ values. The +PEG significantly reduced LA, plant growth, dry matter yield, Ψw, number of stomata per plant and leaf gas exchange, relative to non-PEG condition. Potassium supply alleviated osmotic-induced alterations in Eucalyptus seedlings by better regulating leaf development as well as SD, thus improving the rate of leaf gas exchange parameters, mesophyll conductance to CO2 (lower δ13C ‰ values) and water use efficiency (WUE). Consequently, K-supplied plants under drought better acclimated to osmotic stress than K-deficient plants, which in turn induced lower CO2 assimilation and dry matter yield, as well as higher leaf δ13C ‰ and δ15N ‰ values. In conclusion, management practices should seek to optimize K-nutrition to improve WUE, photosynthesis-related parameters and plant growth under water deficit conditions.

Determination of drought tolerance related traits in Helianthus argophyllus, Helianthus annuus, and their hybrids

Drought is a major constraint for sunflower (Helianthus annuus) production worldwide. Drought tolerance traits have been identified in the related wild species Helianthus argophyllus. This study was initiated to develop sunflower drought-tolerant genotypes by crossing cultivated sunflower with this species and analyze drought tolerance traits in the H. annuus and H. argophyllus populations, H. annuus intraspecific hybrids, and H. annuus × H. argophyllus interspecific hybrids along with the commercial hybrid Hysun-33 under three stress regimes: exogenous application of ABA, both by foliar spray and irrigation, and 5% PEG-induced osmotic stress. H. argophyllus populations had a significantly lower leaf area and higher water-use efficiency and leaf cuticular wax content under all treatments, and maintained a higher net photosynthetic rate and stomatal conductance under osmotic stress. Small leaf area and high cuticular waxes content of the wild species were, however, not inherited in interspecific hybrids which suggested for selection in F₂ for these traits. Therefore, transgressive plants were selected in the F₂ population to establish F₃ plant progenies with silver-leafed canopy of H. argophyllus which showed higher achene yield under stress condition. These results are discussed with a view to using H. argophyllus to improve drought tolerance in cultivated sunflower.

Salinity thresholds and genotypic variability of cabbage (Brassica oleracea L.) grown under saline stress

BACKGROUND

Two botanical varieties of cabbage, namely Savoy (Brassica oleracea var. Sabauda L.) and White (Brassica oleracea var. Capitata L.) were used in order to understand the morphological, physiological and biochemical elements of functional salt stress response. Thirteen salt concentrations (range, 0 to 300 mmol L(-1) NaCl) were considered in Experiment 1 and, of these 13, three (0, 100 and 200 mmol L(-1) NaCl) were used in Experiment 2.

RESULTS

Experiment 1 enabled the definition of two salinity thresholds (100 and 200 mmol L(-1) NaCl), associated with morphological and physiological adaptations. In Experiment 2, moderate salinity (100 mmol L(-1) NaCl) had lower effects on Savoy than in White cabbage yield (respectively, -16% and -62% from control). Concurrently, 100 mmol L(-1) NaCl resulted in a significant increase of antioxidant enzymes from control conditions, that was greater in Savoy (+289, +423 and +88%, respectively) as compared to White (+114, +356 and +28%, respectively) cabbage. Ion accumulation was found to be a key determinant in tissue osmotic adjustment (mainly in Savoy) whereas the contribution of organic osmolites was negligible.

CONCLUSIONS

Higher antioxidative enzymatic activities in Savoy versus White cabbage after treatment with 100 mmol L(-1) NaCl were associated with improved water relations, thus suggesting a possible physiological pathway for alleviating perceived salt stress.