Effects of the interaction between drought and shade on water relations, gas exchange and morphological traits in cork oak (Quercus suber L.) seedlings

The combined effect of drought and light on different physiological and biochemical traits was assessed in cork oak (Quercus suber L.) seedlings grown under two levels of light availability and submitted to a long-standing drought. Watering was withdrawn after germination and seedlings were allowed to dry to a water content of ca. 50% of field capacity. At this point, water-stressed seedlings were grown under moderate drought and two light regimes: high light (HL—50%) and low light (LL—2%). Soil water in control plants was kept close to field capacity (90–100%) for both light environments. Water-relations parameters derived from P–V curves, gas exchange and water status at predawn (Ψ_pd) were evaluated at twice during the experiment. Nitrogen and chlorophyll contents were determined in the same leaves used for the gas exchange measurements. In addition, maximum rate of carboxylation (V_cmax) and electronic transport (J_max) were derived from A–C_i curves in well-watered seedlings.

The variation on moisture availability during the experiment was the same under both light environments. In control plants, Ψ_pd was over −0.3 MPa at the two harvests, while stressed seedlings decreased to −0.9 MPa, with no differences between light treatments. Water stress decreased osmotic potentials at full (Ψπ₁₀₀) and zero turgor (Ψπ₀). The regressions between both potentials and Ψ_pd showed a higher intercept in shade grown seedlings. This fact will point out the higher osmoregulation capacity in sun seedlings whatever water availability.

Nitrogen investment on a per leaf mass (N_mass), chlorophyll content (Chl_mass) and SLA tended to show a typical pattern of sun-shade acclimation. Thus, the three parameters increased with shade. Only for N_mass there was a significant effect of watering, since water stress increased N_mass.

LL plants showed a lower photosynthetic capacity in terms of maximum net photosynthesis at saturating light (A_max), which was related to a decrease in V_cmax and J_max. Both parameters varied with specific leaf area (SLA) in a similar way. The low-light environment brought about a higher nitrogen investment in chlorophyll, while under high-light environment the investment was higher in carboxylation (V_cmax) and electronic transport (F_max).

Stomatal conductance to water vapour (g_wv) and A_max were lower in low-light seedlings independently of watering. In addition, there was a trend to keep higher intrinsic water use efficiency (IWUE) under high light environment. The increase of IWUE under water stress was higher in HL seedlings. This was as consequence of the steeper decline in g_wv as Ψ_pd decreased. The decrease of A_max with Ψ_pd occurred in a similar way in LL and HL seedlings. Thus, the HL seedlings tended to sustain a higher ability to increase IWUE than LL seedlings when they were submitted to the same water stress.     

Biometrical, biological, biochemical and molecular characteristics of Meloidogyne incognita isolates and related species

Meloidogyne incognita is one of the most polyphagous species of root-knot nematodes occurring in Brazil and worldwide. Eight M. incognita isolates were studied, representing two enzymatic phenotypes (esterase and malate desydrogenase: I1/N1, I2/N1) and four cryptic Meloidogyne sp.1 (S2/N1) isolates, representing one cytological type (3n?=?40–46). Three M. hispanica isolates (Hi3/N1, 2n?=?32–36) and two of an atypical Meloidogyne sp.2 (S2a/N3, 3n?=?40–44) were included in this study for comparison. All isolates were tested with three M. incognita-specific molecular markers. The primer pairs B06F/R, miF/R and incK14F/R amplified three species-specific fragments of 1,200?bp, 955?bp and 399?bp, respectively for M. incognita and Meloidogyne sp.1 isolates. No amplification occurred in the M. hispanica and Meloidogyne sp.2 isolates, except with primers miF/R (1,650?bp). The genetic variability of the Meloidogyne spp. isolates was evaluated, using RAPD and ISSR markers. The phylogenetic analyses revealed two strongly supported monophyletic clades: clade I, consisting of M. hispanica and the atypical Meloidogyne sp.2 isolates, and clade II, clustering together all M. incognita and the Meloidogyne sp.1 isolates. Considering the biometrical, cytological and molecular approaches, it was possible to conclude that the isolates with three enzymatic phenotypes (I1/N1, I2/N1 and S2/N1) presented the characteristics described for M. incognita. Some correlations were detected between the isozymatic phenotypes and the tree topology (S2a/N3, Hi3/N1, I1/N1, S2/N1), but no strict correlation could be observed for the phenotype I2/N1 and one isolate of S2/N1. Morphologically, the Msp.2 isolates differ from M. incognita and M. hispanica by the female stylet features presenting straight cone tip and round pear shaped knobs, posteriorly sloping. The results of this study suggested that the Msp.2 isolates with phenotypes S2aN3 belong to a new or an unidentified species closely related to M. hispanica.     

Outbreaks of proliferative haemorrhagic enteropathy on two pig farms

SUMMARY Clinical signs of proliferative haemorrhagic enteropathy (PHE) including anaemia, dysentery and sudden death were observed in finisher pigs and young breeding stock on 2 farms. On farm A, PHE occurred 12 months after repopulation of the farm. Other outbreaks of PHE occurred after the withdrawal of therapeutic concentrations of in-feed antibacterial agents (farm A), or after monensin sodium (100 g/t) replaced olaquindox (100 g/t) in feed (farm B). The outbreaks, the possible sources of contamination and the role of antibacterial feed additives in the treatment and control of PHE are described.     

Functional Feeds to Tackle Meagre (Argyrosomus regius) Stress: Physiological Responses under Acute Stressful Handling Conditions

Marine algae are recognised sources of bioactive compounds that have attracted great interest as nutritional supplements for aquaculture fish. Intensive rearing conditions often expose fish to husbandry-related stressors, rendering fish more susceptible to disease and reducing production yields. The present work evaluated the potential of two marine algae extracts (Fucus vesiculosus and Nannochloropsis gaditana) as nutritional supplements to mitigate stress effects in meagre (Argyrosomus regius) exposed to an acute handling stress (AS). A plant-based diet was used as a control, and three other diets were prepared, which were similar to the control diet but supplemented with 1% of each algal extract or a combination of the two extracts (0.5% each). The effects of supplemented diets on stress biomarkers, antioxidant enzyme activities, and immune response were analysed in fish exposed to AS after 4 weeks of feeding. Supplemented diets did not affect growth performance but the inclusion of F. vesiculosus promoted higher feed efficiency, as compared to the control group. Dietary algal extracts supplementation reduced plasma glucose levels, increased white blood cell counts, and reduced the expression of pro-inflammatory genes when compared with the control. N. gaditana supplementation led to a reduction in hepatic antioxidant enzyme activity and glutathione levels, while F. vesiculosus supplementation increased muscle glutathione reductase activity and reduced lipid peroxidation. These findings support the potential of algal extracts as nutraceuticals in aquafeeds to enhance the ability of fish to cope with husbandry-related stressful conditions and ultimately improve fish health and welfare.     

Immunisation of pigs with a major envelope protein sub-unit vaccine against porcine reproductive and respiratory syndrome virus (PRRSV) results in enhanced clinical disease following experimental challenge

Disease exacerbation was observed in pigs challenged with virulent porcine reproductive and respiratory syndrome virus (PRRSV) following immunisation with a recombinant GP5 sub-unit PRRSV vaccine (rGP5) produced in E. coli. Eighteen animals were divided into three experimental groups: group A were immunised twice IM with rGP5, 21 days apart; group B acted as positive controls (challenged but not immunised); and group C were negative controls. Pigs in groups A and B were challenged 21 days after the second immunisation of the group A animals. Following challenge, three pigs given rGP5 exhibited more severe clinical signs than the positive controls, including respiratory distress and progressive weight-loss. Although not statistically significant, the more severe disease exhibited by group A animals may suggest previous immunisation as a contributory factor. The mechanisms of these findings remain unclear and no association could be established between the severity of disease, non-neutralising antibody concentrations and tissue viral loads.     

Herpes viral hepatitis in a toucan

Herpesvirus infection was diagnosed in a toucan. The herpesvirus was isolated from the liver and identified by electron microscopy in the liver and in cell culture. A negative immunofluorescent reaction was obtained when virus-infected cell cultures were reacted with a conjugate to the herpesvirus of Pacheco's disease. The main pathologic finding in the toucan consisted of a severe necrotizing hepatitis with intranuclear inclusions in the liver and spleen. A presumptive diagnosis of chlamydiosis was also made, based on a positive direct fluorescent monoclonal antibody reaction to chlamydial antigens in impression smears of liver and spleen. Chlamydial isolation attempts were unsuccessful. The toucan had been in contact with two macaws that had died 5 days before the toucan died and were diagnosed by histology as having herpesvirus hepatitis.