The influence of different levels of dietary vitamin E on sea bass Dicentrarchus labrax flesh quality

Sea bass Dicentrarchus labrax fillet quality was investigated after feeding with four diets (A, B, C or D) containing different levels of dietary vitamin E (139 mg kg^–1, 254 mg kg^–1, 493 mg kg^–1 and 942 mg kg^–1, respectively). Six-hundred and eighty fish (mean initial weight 208 g) were equally divided into four 20 m³ tanks and fed for 87 days. Filtered seawater with a temperature ranging from 18.2 to 26.3 °C was supplied continuously. At the end of the experiment, fish were stored at 1 °C for 12 days. At one, three, six, nine and 12 days, 20 fish per group were processed for proximate composition, vitamin E and induced thiobarbituric acid reactive substances (TBARs) analyses. No significant differences in proximate composition were registered between groups. The flesh lipid content ranged from 88.0 g kg^–1 (group B) to 96.8 g kg^–1 (group A). Vitamin E fillet content was significantly different between groups, reaching levels of 98.0, 150.7, 225.2 and 302.0 μg g^–1 lipids for group A, B, C and D, respectively. Induced TBARs values were statistically different only for group A compared with the other groups. No significant variations were registered in relation to preservation time. Because of the positive influence of vitamin E on seafood quality and the correlation between its dietary level and flesh deposition, the α-tocopherol content of the diet should be well above fish minimum requirements.     

Quantifying reductions in consumptive water use under regulated deficit irrigation in pistachio (Pistacia vera L.)

The reduction in agricultural water use in areas of scarce supplies can release significant amounts of water for other uses. As improvements in irrigation systems and management have been widely adopted by fruit tree growers already, there is a need to explore the potential for reducing irrigation requirements via deficit irrigation (DI). It is also important to quantify to what extent the reduction in applied water through DI is translated into net water savings via tree evapotranspiration (ET) reduction. An experiment was conducted in a commercial pistachio orchard in Madera, CA, where a regulated deficit irrigation (RDI) program was applied to a 32.3-ha block, while another block of the same size was fully irrigated (FI). Four trees were instrumented with six neutron probe access tubes each, in the two treatments and the soil water balance method was used to determine tree ET. Seasonal irrigation water in FI, applied through a full-coverage microsprinkler system, amounted to 842 mm, while only 669 mm were applied in RDI. Seasonal ET in FI was 1024 mm, of which 308 mm were computed as evaporation from soil (E_s). In RDI, seasonal ET was reduced to 784 mm with 288 mm as Es. The reduction in applied water during the deficit period amounted to 147 mm. The ET of RDI during the deficit period was also reduced relative to that of FI by 133 mm, which represented 33% of the ET of FI during the deficit irrigation period. There was an additional ET reduction in RDI of about 100 mm that occurred in the post-deficit period.     

Environmental and irrigation conditions can mask the effect of Magnaporthiopsis maydis on growth and productivity of maize

Maize production in temperate countries is threatened by late wilt, caused by Magnaporthiopsis maydis. Plant infection occurs early after sowing, but symptoms appear from flowering onwards. The disease is mainly controlled by genetic resistance, which is often partially expressed in the field. Development of disease symptoms is also highly dependent on environmental conditions. This study looked at whether production and growth of susceptible maize are affected by M. maydis under environmental conditions that are suboptimal for disease development. In addition, the effect of water availability on disease development under optimal conditions was determined. Pot experiments were conducted in an open-air enclosure in 2013, 2015 and 2016. Under unfavourable conditions for disease (low air temperature and relatively high air humidity), aboveground symptoms did not appear in the plants despite growth and production variables being clearly altered by the fungus. When air temperatures and humidity were optimal for disease development (air temperatures relatively high and humidity rather low), leaf symptoms on inoculated plants became apparent but with secondary importance compared to decreases in growth and production. The pathogen also affected the root:aboveground biomass ratio to a greater extent when the plants were under good water conditions than under deficit irrigation. Under optimal conditions and with good soil water content, the infected crop may end its cycle without symptoms, with the disease undetected, although reductions in yield and aboveground biomass can occur.     

Spatial sap flow and xylem anatomical characteristics in olive trees under different irrigation regimes

The compensation heat pulse (CHP) method is widely used to estimate sap flow and transpiration in conducting organs of woody plants. Previous studies have reported a natural azimuthal variability in sap flow, which could have practical implications in locating the CHP probes and integrating their output. Sap flow of several olive trees (Olea europaea L. cv. 'Arbequina') previously grown under different irrigation treatments were monitored by the CHP method, and their xylem anatomical characteristics were analyzed from wood samples taken at the same location in which the probes were installed. A significant azimuthal variability in the sap flow was found in a well-irrigated olive tree monitored by eight CHP probes. The azimuthal variability was well related to crown architecture, but poorly to azimuthal differences in the xylem anatomical characteristics. Well-irrigated and deficit-irrigated olive trees showed similar xylem anatomical characteristics, but they differed in xylem growth and in the ratio of nocturnal-to-diurnal sap flow (N/D index). The results of this work indicate that transpiration cannot be accurately estimated by the CHP method in olive trees if a small number of sensors are employed and that the N/D index could be used as a sensitive water status indicator.     

Water requirements of olive orchards–II: determination of crop coefficients for irrigation scheduling

Intensification of olive cultivation by shifting a tree crop that was traditionally rain fed to irrigated conditions, calls for improved knowledge of tree water requirements as an input for precise irrigation scheduling. Because olive is an evergreen tree crop grown in areas of substantial rainfall, the estimation of crop evapotranspiration (ET) of orchards that vary widely in canopy cover, should be preferably partitioned into its evaporation and transpiration components. A simple, functional method to estimate olive ET using crop coefficients (K _c=ET/ET₀) based on a minimum of parameters is preferred for practical purposes. We developed functional relationships for calculating the crop coefficient, K _c, for a given month of the year in any type of olive orchard, and thus its water requirements once the reference ET (ET₀) is known. The method calculates the monthly K _c as the sum of four components: tree transpiration (K _p), direct evaporation of the water intercepted by the canopy (K _pd), evaporation from the soil (K _s1) and evaporation from the areas wetted by the emitters (K _s2). The expression used to calculate K _p requires knowledge of tree density and canopy volume. Other parameters needed for the calculation of the K _c’s include the ET₀, the fraction of the soil surface wetted by the emitters and irrigation interval. The functional equations for K _p, K _pd, K _s1 and K _s2 were fitted to mean monthly values obtained by averaging 20-year outputs of the daily time step model of Testi et al. (this issue), that was used to simulate 124 different orchard scenarios.     

Use of an acoustic telemetry array for fine scale fish behaviour assessment of captive Paiche,Arapaima gigas,breeders

As Arapaima gigas is one of the most valuable species for the growing production of Amazonian aquaculture, knowledge of its reproductive behaviour and its application to increase reproduction success in captivity is of great importance as no hormonal spawning induction technique exists for this species. An acoustic positioning system (LOTEK Inc.) was used to observe the interactions of adult fish to better understand the formation of mating pairs. Fish were placed in a 4,500 m² aquaculture pond over a 6‐month period in the IIAP field station of Pucallpa, Perú. This paper describes the methodological protocols used to set up and test the hydrophone array and presents the methodology used for the analysis of the huge amount of collected data. This methodology is illustrated by the analysis of a 6‐day period for a mating pair that showed a spawning event. The results indicated that male and female occupied mostly one preferential area in one pond edge where the nesting area is located. Different activity patterns were observed during the spawning event, with male and female being closer during the spawning day. The results also showed that male travelled less distance than female during the studied period. Finally these results demonstrated the suitability of such equipment to monitor fish interactions at fine spatial (sub meter) and temporal (5 s) scales in confined environments like aquaculture ponds.     

Water requirements of olive orchards: I simulation of daily evapotranspiration for scenario analysis

Water requirements of olive orchards are difficult to calculate, since they are influenced by heterogeneous factors such as age, planting density and irrigation systems. Here we propose a model of olive water requirements, capable of separately calculating transpiration (E _p), intercepted rainfall evaporation (E _pd) and soil evaporation (E _s) from the wet and dry fraction of the soil surface under localized irrigation. The model accounts for the effects of canopy dimension on E _p and of the wetted soil surface fraction on E _s. The model was tested against actual measurements of olive evapotranspiration (ET) obtained by the eddy covariance technique in a developing olive orchard during 3 years. The predicted ET and crop coefficients showed good agreement with the measured data. The model was then used to simulate the average water requirements of two mature orchards using 20-year meteorological datasets of Cordoba (Spain) and Fresno (CA, USA). Average annual ET of a 300 trees ha⁻¹ orchard at Cordoba was 1,025 mm, while the same orchard at Fresno had an average ET of 927 mm. Transpiration losses were 602 mm at Cordoba and 612 mm at Fresno. Evaporation from the soil can have a large effect on olive ET; thus, olive crop coefficients (K _c) are very sensitive to the rainfall regime.