Effectiveness of arbuscular mycorrhizal fungi in the protection of date palm (Phoenix dactylifera L.) against bayoud disease

In the present study, arbuscular mycorrhizal fungi (AMF) (Glomus monosporus, Glomus deserticola, Glomus clarum and a complex of native AMF coming from the Aoufous date palm grove in the south of Morocco) have been shown to protect date palm seedlings against bayoud disease. Treatment with AMF reduced disease severity by 8–77% depending on the AMF isolate used. In addition, all mycorrhizal fungi stimulate significantly shoot height and biomass and increase the number of leaves per plant. The plants associated with Aoufous complex present the best improvement of plant growth and great effectiveness in reducing bayoud disease incidence. Moreover, the AMF induce change in activities of two defence-related enzymes (peroxidases and polyphenoloxidases). The potential involvement of this induced biochemical defence reaction in protecting date palm against bayoud is discussed.     

Sodium‐induced calcium deficiency in sugar beet during substitution of potassium by sodium

Functions of sodium (Na⁺) and potassium (K⁺) are closely associated. In some crops, Na⁺ is able to prevent or reduce considerably the occurrence of K⁺ deficiency. Sugar beet (Beta vulgaris L.) is a natrophilic crop, and positive effects of Na⁺ applications on yield were observed when K⁺ was sufficiently supplied. However, it is not known which specific function of K⁺ can limit the growth of sugar beet when K⁺ is substituted by an equivalent amount of Na⁺. Therefore, K⁺ substitution by Na⁺ was investigated for sugar beet in hydroponics. Surprisingly, no K⁺‐deficiency symptoms were observed. However, calcium (Ca²⁺) concentrations in the leaves were significantly decreased. Moreover, Ca²⁺ uptake and translocation through xylem sap were reduced in Na⁺‐treated plants. It is concluded that Ca²⁺ uptake by roots and its translocation via xylem sap primarily limit the possibility of K⁺ substitution by Na⁺ in sugar beet nutrition.     

Estimating the variability of tillage forces on a chisel plough shank by modeling the variability of tillage system parameters

In this paper, a probabilistic approach is proposed for quantifying the variability of the tillage forces for the shank of a chisel plough with narrow tines and to estimate the failure probability. An existing three-dimensional analytical model of tool forces from McKyes was used to model the interaction between the tillage tools and the soil. The variability of tillage forces was modeled, taking into account the variability of soil engineering properties, tool design parameters and operational conditions. The variability of the soil engineering properties was modeled by means of experimental observations. The dispersion effect of each tillage system parameter on the tillage forces was determined by a sensitivity analysis. The results show that the variability of the horizontal and vertical forces follows a lognormal distribution (μ = 0.872, ξ = 0.449; μ = 0.004, ξ = 0.447) and the relationship between these forces is positive and quasi-linear (ρ(P_H, P_v) = 0.93).This lognormal variability was integrated into the estimation of the failure probability for the shank by using Monte Carlo simulation (MCS) and the first-order reliability method (FORM). The results obtained by these two methods, with the assumption of non-correlation between the horizontal and vertical forces, were almost identical. However, the FORM method was faster and simpler, compared to the MCS technique. Furthermore, the correlation between the horizontal and vertical forces has no significant effect on the failure probability, regardless of the correlation strength. Therefore, it is concluded that the FORM method can be used to estimate the failure probability without considering the correlation between horizontal and vertical forces.     

Mechanical and structural changes in multimode optical fibers induced by aging in harsh gaseous and liquid reagents

The increased optical fiber development for a variety of physical and chemical measurements using smart structures and sensors leads to investigate the mechanical and chemical reliability of standard commercial acrylate polymer coated fibers. Multimode optical fiber was subjected to aggressive chemical reagents in gaseous and liquid phase, such as acetylene, ammonia, dimethyl-sulfoxide for different durations after prior vacuum exposure. Tensile testing results were treated using Weibull statistic. A comparison of mean failure strengths of aged fibers for similar exposure duration has revealed the highest sensitivity to acetylene and dimethyl-sulfoxide reagents. Based on analysis of aged fiber surface morphology obtained from Scanning Electron Microscopy, we can deduce the damage extent and the consequence on the structure of the fiber in contact with these harsh environments.     

Cross-pathogenicity of <Emphasis Type="Italic">Verticillium dahliae</Emphasis> between potato and sunflower

This study examined cross-pathogenicity of the soilborne pathogen Verticillium dahliae between potato and sunflower. Four week-old potato and sunflower seedlings were inoculated with ten isolates from each of the two host species. Potato cultivars (Kennebec, susceptible, and Ranger Russet, moderately resistant) and sunflower hybrids (IS8048, susceptible, and 6946, moderately resistant) were assessed for disease severity and percent infection at 2 weeks, 3 weeks, 4 weeks, 5 weeks, and 6 weeks after inoculation (w.a.i), and for vascular discolouration at 6 w.a.i., using visual scales developed for each host species. The experiments were conducted in 2006 and repeated in 2007. Based on percent infection and disease severity, most V. dahliae isolates were highly aggressive on both host species. The tested isolates caused higher disease levels in the susceptible than in the moderately resistant phenotypes. They also caused more vascular discolouration in their original than in the alternative host. However, the isolates originating from sunflower caused less infection and disease severity on both hosts, compared to their potato counterparts. Cluster analysis based on all of the criteria used to assess pathogenicity led to three groups of isolates: (i) most V. dahliae potato isolates, which ranged with the highly aggressive control isolates, (ii) one V. dahliae sunflower isolate, which showed a similar pathogenicity level to the weakly-aggressive V. albo-atrum sub-group II control isolate, with no more symptoms than in the non-inoculated plants, and (iii) most V. dahliae sunflower isolates with mildly- to weakly-aggressive levels. Based on these results, V. dahliae cross-pathogenicity is very effective between potato and sunflower. Therefore, rotations involving these species should be avoided, especially where sunflower follows potato.     

Immunomodulatory effect of dietary brewer’s yeast extract in Sander lucioperca juveniles against the challenge of Aeromonas salmonicida

The present study examined the influence of extract obtained from the interior of cells of yeast, Saccharomyces cerevisiae (NuPro^®), on the growth, proximate composition, nonspecific cellular and humoral defense mechanisms, and protection against furunculosis in pikeperch (Sander lucioperca). It was noted that eight weeks of supplementation with 40 g of NuPro^® kg^?1 feed (containing approximately 0.22 % exogenic nucleotides) enhanced pikeperch innate immunity. Increased serum lysozyme activity and total Ig levels (P < 0.05) were noted in the NuPro^®-fed group, which indicated the activation of nonspecific humoral defense mechanisms. Brewer’s yeast extract also stimulated nonspecific cellular defense mechanisms as indicated by the increased metabolic activity of blood phagocytes and pronephric macrophages, and in the increased intracellular killing activity of phagocytes and proliferative responses of T and B lymphocytes (P < 0.05). Additionally, reduced mortality (15 %) after the in vivo challenge with pathogenic Aeromonas salmonicida suggested that NuPro^® activated nonspecific protection against furunculosis in pikeperch. The experimental feed did not have a significant impact on the growth or proximate composition of the fish (P > 0.05).     

Production Economics of Nile Tilapia (Oreochromis niloticus) Pond Culture in El-Fayum Governorate,Egypt

Econometric techniques were used to estimate a production function for tilapia pond culture in El-Fayum Governorate, Egypt, utilizing cross-sectional field data. Explanatory variables were feed, initial stocking weight, and pond size. The function was used to examine returns to scale, estimate the productivity of feed and initial stocking weight, and estimate the profit maximizing demand equations for feed and fingerlings. Diminishing returns to scale seem to exist for tilapia pond culture. Optimal economic stocking and feeding rates, yield, and profits for the whole sample were estimated at prevailing prices. Results indicated that producers were using stocking rates greater than the optimal by 36% to 115% and using insufficient feed by 8% to 22%. Investigation of the effects of changes in tilapia selling price and feed price on optimal stocking and feeding rates, yield, and profits showed that a change in tilapia selling price has greater effect on profits, yield, stocking, and feeding rates than a proportional change in feed price. Profits, feeding, and stocking rates are more sensitive than yield to changes in selling price, while feeding rate is more sensitive than stocking rate, yield, and profits to changes in feed price.     

Enhancing the growth of Nile tilapia larvae/juveniles by replacing plant (gluten) protein with algae protein

Diets incorporating different levels of corn gluten meal replacement using biofuel algae or Spirulina protein at 0%, 25%, 50%, 75% and 100% were evaluated for larval/juvenile stage of Nile tilapia (Oreochromis niloticus). Fish averaging 0.02 g were divided into groups of 50. There were three replicates per every dietary treatment that were fed one of six diets for 11 weeks. Corn gluten protein was replaced with algae on the protein basis. All diets were supplemented with 1.5% lysine and 0.5% methionine. The experimental diets were formulated to contain 37 ± 2.8% protein and 14 ± 4.3% lipid in the form of fish oil and soybean lecithin (phospholipids source). The results indicated that algae positively affected feed consumption and fish growth up to the 50% replacement and then performance was depressed. Significant differences in concentration of individual minerals (Al, Fe, Zn and Cu) in the whole fish body were found. Mineral composition of algae might have affected growth when diets which contained more than 75% of plant protein were replaced with microalgae. These findings suggest that up to 50% of dietary corn gluten meal protein can be replaced with microalgae which significantly enhance fish growth.