No abstract

SummaryIn certain soils populations of plant-parasitic nematodes (PPN) decline. Understanding this effect may open up environmentally friendly management options. We identified such a suppressive soil containing virtually no PPN. Inoculated Meloidogyne hapla declined in this soil more than in a control soil and reproduction on tomato was reduced. The extracted soil microbiome alone decreased root invasion of second-stage juveniles (J2) and progeny as well as the native soil. We tested the antagonistic potential against PPN that differ in life strategies. The microbiome was most suppressive against two populations of M. hapla and one population of Pratylenchus neglectus, and least suppressive against M. incognita and the ectoparasite Hemicycliophora conida. In a split-root system with M. hapla, plant-mediated but not direct effects of the microbiome significantly reduced root invasion of J2, while direct exposure of M. hapla to the microbiome significantly affected reproduction. Overall, both plant-mediated and direct effects of the microbiome were responsible for the soil suppressiveness against M. hapla.

Maintaining xylem water transport under drought is vital for plants, but xylem failure does occur when drought-induced embolisms form and progressively spread through the xylem. The hydraulic method is widely considered the gold standard to quantify drought-induced xylem embolism. The method determines hydraulic conductivity (Kh) in cut branch samples, dehydrated to specific drought levels, by pushing water through them. The technique is widely considered for its reliable Kh measurements, but there is some uncertainty in the literature over how to define stable Kh and how that relates to the degree of xylem embolism formation. Therefore, the most common setup for this method was extended to measure four parameters: (i) inlet Kh, (ii) outlet Kh, (iii) radial flow from xylem to surrounding living tissue and (iv) the pressure difference across the sample. From a strictly theoretical viewpoint, hydraulic steady state, where inflow equals outflow and radial flow is zero, will result in stable Kh. Application of the setup to Malus domestica Borkh. branches showed that achieving hydraulic steady state takes considerable time (up to 300 min) and that time to reach steady state increased with declining xylem water potentials. During each experimental run, Kh and xylem water potentials dynamically increased, which was supported by X-ray computed microtomography visualizations of embolism refilling under both high- (8 kPa) and low-pressure (2 kPa) heads. Supplying pressurized water can hence cause artificial refilling of vessels, which makes it difficult to achieve a truly stable Kh in partially embolized xylem.

The current use and distribution of agricultural water resources is highly prone to effects of global climate change due to shifting precipitation patterns. The production of vegetable crops in open field cultivation often requires demanding water applications, being impaired in regions where climate change will increasingly evoke water scarcity. To date, increasingly occurring precipitation-free periods are already leading to moderate water deficits during plant growth, e.g., in southern Europe. Among all vegetable crops, leafy vegetables such as spinach (Spinacia oleracea L.) are particularly vulnerable to limited water supply, because leaf expansion is highly dependent on water availability. Besides biomass production, water limitation might also affect the valuable nutritional composition of the produce. Therefore, we investigated the impact of moderately reduced water supply on the chemical composition of spinach, cultivated in the open field in three consecutive years. Two different water supply treatments, full and reduced irrigation, were used in a randomized block design consisting of three sets of six plots each. In the reduced water supply treatment, the total amount of supplied water, including both irrigation and natural precipitation, amounted to 90%, 94% and 96% in 2015, 2016 and 2017, respectively, of the full, optimal water supply treatment. Spinach grown under limited water supply showed significantly higher fresh biomass-based contents of polyols (e.g., inositol, glycerol), ascorbic acid, potassium, nitrogen, phosphorous, zinc and manganese, as well as total flavonoids and carotenoids. Increased dry biomass-based levels were found for total inositol, zinc and manganese, as well as decreased levels for malic acid, fumaric acid, phosphate and chloride. Furthermore, we report a high seasonal variation of several minor phytochemicals, such as single flavonoids. Spinacetin derivatives, spinatoside-glucoside as well as a rather unusual hexuronylated methylenedioxy flavonoid showed highest amounts when grown under relatively low irradiation in autumn. Levels of patuletin derivatives tended to increase under high irradiation conditions during spring. In summary, the chemical composition of spinach was shown to be highly sensitive to moderately reduced water supply and seasonal variation, but the overall nutritional quality of fresh marketable spinach was only marginally affected when considering health-related constituents such as minerals, trace elements, flavonoids and carotenoids.

Vegetable production requires high nutrient input for ensuring high quality and high yield. As this is ecologically disadvantageous, it is necessary to determine if nitrogen (N) fertilization can be reduced without negative effects on productivity. For quality reasons, the effects of reduced N supply on taste, valuable compounds and storage life must be elucidated in parallel. This study examines whether reducing the N supply of cocktail tomatoes by 50% to recommendations affects the yield and quality of tomato fruits. Three varieties with different skin colors, yellow-orange (‘Apresa’), red (‘Delioso’) and brown (‘Bombonera’), were grown in soil in a greenhouse and harvested at the red-ripen stage. Quality parameters were assessed at harvest and after eight-day storage. Total yield decreased exclusively with ‘Bombonera’ due to reduced fruit weight. Firmness of the fruit pulp, concentrations of minerals, soluble solid contents, total acidity, total phenolics and liposoluble pigments of fruits were not influenced. However, storage affected chemical compositions positively, as shown by increased antioxidants. Descriptive sensory analyses revealed no impact of reduced N supply. From the perspective of the yield, quality and shelf life of fruits, reducing the N supply by 50% offers opportunities for the three cocktail tomato varieties in soil cultivation.