Arbuscular mycorrhizal fungi and soil aggregation in a no‐tillage system with crop rotation

Crop rotation adoption in no‐tillage systems (NTS) has been recommended to increase the biological activity and soil aggregation, suppress soil and plant pathogens, and increase the productivity aiming at the sustainability of agricultural areas. In this context, this study aimed to assess the effect of crop rotation on the arbuscular mycorrhizal fungi (AMF) community and soil aggregation in a soil cultivated for nine years under NTS. Treatments consisted of combinations of three summer crop sequences and seven winter crops. Summer crop sequences consisted of corn (Zea mays L.) monoculture, soybean (Glycine max L. Merrill) monoculture, and soybean–corn rotation. Winter crops consisted of corn, sorghum (Sorghum bicolor (L.) Moench), sunflower (Helianthus annuus L.), sunn hemp (Crotalaria juncea L.), pigeon pea (Cajanus cajan (L.) Millsp.), oilseed radish (Raphanus sativus L.), and millet (Pennisetum americanum (L.) Leeke). Soil samples were collected at a depth of 0–0.10 m for analyses of soil chemical, physical, and biological attributes. Spore abundance, total glomalin, and soil aggregate stability index were higher in the soil under corn monoculture. The highest values of aggregate mean weight diameter were observed in the soybean–corn rotation (3.78 mm) and corn monoculture (3.70 mm), both differing from soybean monoculture (3.15 mm), while winter crops showed significant differences only between sorghum (3.96 mm) and pigeon pea (3.25 mm). Two processes were identified in the soil under summer crop sequences. The first process was observed in PC1 (spore abundance, total glomalin, easily extractable glomalin, pH, P, and Mg²⁺) and was related to AMF; the second process occurred in PC2 (aggregate mean weight diameter, soil aggregate stability index, K⁺, and organic matter) and was related to soil aggregation. The nine‐year no‐tillage system under the same crop rotation adoption influenced AMF abundance in the soil, especially with corn cultivation in the summer crop sequence, which promoted an increased total external mycelium length and number of spores of AMF. In addition, it favored an increased soil organic matter content, which is directly related to the formation and stability of soil aggregates in these managements.     

Establishing the optimal essential amino acid ratios in juveniles of Nile tilapia (Oreochromis niloticus) by the deletion method

One of the strategies used to improve fish production is lowering the feed costs and the environmental impact by reducing dietary protein content. Using the deletion method, we determined the optimal amino acid (AA) ratio for Nile tilapia (Oreochromis niloticus) (body weight 20 g). Eleven experimental diets and four replications, taken two at a time, distributed in a randomized block design were used. For this trial, a balanced diet (BD) was formulated. Ten other diets were formulated by the deletion method, in which the BD diet was adjusted to result in a reduction of 45% of the test amino acid. Fish were fed three times a day for 57 days. Groups of fish at the beginning and at the end of the experiment were euthanized for further determination of the carcass nitrogen (N) composition. The optimal ratio of each AA was derived by dividing the requirement for each AA by the requirements for lysine. The essential AA ratios, expressed relative to lysine (=100), were methionine 64, threonine 93, tryptophan 24, arginine 125, histidine 34, isoleucine 57, leucine 96, valine 76 and phenylalanine 101. Our findings might be used to design strategies aimed at reducing the production costs of Oreochromis niloticus.     

Effects of tributyltin and hypoxia on the progression of Perkinsus marinus infections and host defence mechanisms in oyster, Crassostrea virginica (Gmelin)

Oysters, Crassostrea virginica (Gmelin), naturally infected by the protozoan parasite Perkinsus marinus in the field were exposed for 6 weeks to tributyltin (TBT), hypoxia, or to both stressors simultaneously. The TBT-exposed oysters continuously bioaccumulated TBT, reaching about 4 mg kg^??1 dry weight by 6 weeks; hypoxic oysters were exposed to water containing an average dissolved oxygen level of about 3 mg L^??1. Untreated control oysters suffered about 30% cumulative mortality by 6 weeks as a result of the progression of their P. marinus infections. The TBT treatment alone produced no additional mortality; however, cumulative mortality in hypoxic oysters was elevated. Mortality among oysters receiving both TBT and hypoxia significantly exceeded that caused by either stressor alone, suggesting a synergistic effect. In an attempt to identify immunotoxicological mechanisms underlying stress-related augmentation of P. marinus infections, defence-related immune functions were measured at 3 and 6 weeks in control and treated oysters. In general, the total number of haemocytes increased as the infections progressed, and the TBT and hypoxic treatments also caused significant additional increments in some samples. However, oxygen-dependent (reactive oxygen species) and oxygen-independent (lysozyme) antimicrobial host defence mechanisms appeared to be largely unaffected by TBT and/or hypoxia. This may be explained by the death of those oysters with marked immunological lesions prior to sampling or by the actual lack of treatment effects.     

Variation in levels of non-starch polysaccharides and endogenous endo-1,4-β-xylanases affects the nutritive value of wheat for poultry

1. Endo-1,4-β-xylanase is known to improve the nutritive value of wheat-based diets for poultry by degrading dietary arabinoxylans. However, broilers’ response to supplementation of wheat-based diets with exogenous endo-1,4-β-xylanase is not always observed.

2. In this study, 108 different wheat lots were analysed for levels of extract viscosity as well as for endogenous endo-1,4-β-xylanase activity, and the impact of these two variables in animal performance was tested.

3. Results revealed that endogenous endo-1,4-β-xylanase activity and extract viscosity content varied widely among different wheat lots. Thus, a trial was conducted to evaluate the efficacy of exogenous enzyme supplementation in broiler diets using wheats with different levels of extract viscosity and endogenous endo-1,4-β-xylanase activity.

4. The data revealed that exogenous enzyme supplementation was only effective when the wheat present in the diet had high levels of extract viscosity (14.8 cP) with low endogenous endo-1,4-β-xylanase activity (347.0 U/kg). Nevertheless, it is apparent that exogenous microbial xylanases reduce digesta extract viscosity and feed conversion ratio independently of the endogenous properties presented by different wheat lots.

5. The data suggest that extract viscosity and/or endogenous endo-1,4-β-xylanase activity affect the response to enzyme supplementation by poultry fed on wheat-based diets.     

Dual disease resistance in a selectively bred eastern oyster, Crassostrea virginica, strain tested in Chesapeake Bay

Selective breeding efforts have yielded oyster strains, Crassostrea virginica, with improved survival and resistance against Haplosporidium nelsoni (MSX); however, because of susceptibility to the oyster pathogen Perkinsus marinus (Dermo), their utility has been limited in areas where the two parasites co-occur. Dual resistance to H. nelsoni and P. marinus was achieved through four generations of artificial selection of wild Delaware Bay oyster progeny at a site in the lower York River, Virginia, USA where both diseases are enzootic. During 1993–1995, survival, growth, and disease susceptibility of third generation Delaware Bay (F₃-DEBY) oysters were evaluated at the York River site in comparison to that of similarly selected third generation James River, Virginia oysters (F₃-JR), and first generation Louisiana oysters (F₁-LA), whose parents were naturally selected in the wild for resistance to P. marinus. During 1997–1999, the performance of F₄-DEBY was evaluated at three sites in Virginia in comparison to two groups of first generation oysters whose parents originated from Mobjack Bay and Tangier Sound, Virginia where both P. marinus and H. nelsoni are enzootic. In the presence of high infection pressure from both H. nelsoni and P. marinus, the F₃-DEBY stock showed significantly higher survival and growth than either the F₃-JR or F₁-LA strain. After 15 months of deployment, 79% of F₃-DEBY, 11% of F₃-JR and 17% of F₁-LA oysters were market size (≥76.2 mm) and cumulative mortality was only 16% in F₃-DEBY as compared to 42% in F₃-JR and F₁-LA. At the termination of the study, F₃-DEBY oysters exhibited 22% lower mortality than the F₁-LA stock, which outperformed the F₃-JR stock. Relative performance in respect to disease varied considerably with sample date; however, average H. nelsoni weighted prevalence varied such that F₃-DEBY1-LA=F₃-JR and average P. marinus weighted prevalence varied such that F₁-LA3-DEBY3-JR. In the 1997–1999 trial, F₄-DEBY oysters experienced 34–61% lower mortality, greater growth rate, and consistently lower prevalence and intensity of P. marinus than either Mobjack Bay or Tangier Sound oysters. H. nelsoni prevalences were very low (<12%) in all three stocks. This is the first study to demonstrate that reduced susceptibility to both P. marinus and H. nelsoni can be achieved through selective breeding.     

Survival to prescribed fire of plantation-grown Corsican black pine in northern Portugal

Context

The current fire regime threatens black pine (Pinus nigra Arn.) persistence in the Mediterranean Basin, which recommends larger-scale fuel treatments. Prescribed burning is an option for stand protection but its use in young stands (which are particularly at risk) is hindered by the scarce knowledge on post-fire tree survival.

Aims

The objectives were to characterize bark thickness as a fire-resistance trait in P. nigra and to describe how post-fire tree survival responds to tree size and fire effects in a 16-year-old plantation.

Methods

Bark thickness was related to diameter at breast height and height in the stem. Metrics describing tree size and stem and crown damage were measured 1?year after prescribed burning in 259 trees. Tree survival was modeled with logistic regression and Classification and Regression Tree analysis.

Results

Bark thickness increased linearly with diameter at breast height (dbh) and decreased with height in the stem. Tree survival was primarily a function of crown injury. Stem damage was an influent factor in small trees.

Conclusion

Due to thinner bark and lower tolerance to crown damage, young P. nigra trees are less fire-resistant than other Mediterranean pines, e.g., Pinus pinaster. Prescribed fire should not be attempted if dbh <10?cm. Mechanical clearing is the treatment of choice in young stands with a significant shrub layer.     

Use of shrimp protein hydrolysate in Nile tilapia (Oreochromis niloticus, L.) feeds

A 45-day feeding trial was carried out to evaluate the use of shrimp protein hydrolysate (SPH) in diets for Oreochromis niloticus, L. SPH was included in isonitrogenous diets replacing fish meal protein by 0, 5, 10, and 20% and offered to Nile tilapia juveniles (1.7 ± 0.4 g) stocked in 40-L glass aquaria. The inclusion of SPH produced no significant differences (P ≥ 0.05) in final weight, survival, weight gain, average daily gain, specific growth rate, feed conversion ratio, protein efficiency ratio, or apparent net protein utilization. The inclusion of SPH Nile tilapia diets significantly affected (P < 0.05) the final fish body composition. Protein and ash contents decreased and fat content increased slightly with the increase in SPH. This study has demonstrated that SPH is a promising protein feedstuff and could account for as much as 6% of Nile tilapia diets with no adverse effects on growth and nutrient utilization.     

Antioxidative properties of cardoon (Cynara cardunculus L.) infusion against superoxide radical,hydroxyl radical,and hypochlorous acid

Polyphenols are able to act as antioxidants by virtue of their hydrogen-donating and metal-chelating capacities. Cardoon (Cynara cardunculus L.) is a species containing considerable amounts of polyphenolic compounds, namely flavonoids and phenolic acids. This study examined the antioxidant activity of cardoon lyophilized infusion against superoxide radical, hydroxyl radical, and hypochlorous acid. Superoxide radical was generated either in an enzymatic system or nonenzymatically, and the scavenging ability was assessed by the inhibition of superoxide radical-induced reduction of nitroblue tetrazolium. Hydroxyl radical was generated by the Fe3+-EDTA/ascorbate Fenton system, and scavenging capacity was estimated by evaluating the inhibition of hydroxyl radical-induced deoxyribose degradation into thiobarbituric acid-reactive substances. Inhibition of hypochlorous acid-induced 5-thio-2-nitrobenzoic acid oxidation to 5,5'-dithiobis(2-nitrobenzoic acid) was used in order to test the hypochlorous acid scavenging activity.     

In vitro predatory activity of nematophagous fungi <Emphasis Type="Italic">Duddingtonia flagrans</Emphasis> on infective larvae of <Emphasis Type="Italic">Oesophagostomum</Emphasis> spp. after passing through gastrointestinal tract of pigs

One isolate of predator fungi Duddingtonia flagrans (AC001) was assessed in vitro regarding the capacity of supporting the passage through pigs' gastrointestinal tract without loss of the ability of preying infective larvae Oesophagostomum spp. Fungal isolates survived the passage and were efficient in preying L₃ since the first 8 h of collection (p < 0.01) in relation to the control group (without fungus). Compared with control, there was a significant decrease (p < 0.01) of 59.6% (8 h), 71.7% (12 h), 76.8% (24 h), 81.0% (36 h), 78.0% (48 h), 76.1% (72 h), and 82.7% (96 h) in means of infective larvae Oesophagostomum spp. recovered from treatments with isolate AC001. Linear regression coefficients of L₃ of recovered Oesophagostomum spp. regarding the collections due to time were −0.621 for control, −1.40 for AC001, and −2.64 for NF34. Fungi D. flagrans (AC001) had demonstrated to be promising for use in the biological control of pig parasite Oesophagostomum spp.