Relation entre I'infestation de Tylenchulus semipenetrans, la morphogenèse et la productivité de l'oranger cv. Maltaise demisanguine greffées sur bigaradier

Les variations pluriannuelles de la croissance végétative (orthotrope et plagiotrope) et de la production et du taux d'infestation des citrus par Tylenchulus semipenetrans suivent une évolution cyclique et des amplitudes décalées les unes par rapport aux autres. Ces variations présentent deux phases distinctes. La première se caractérise par une diminution de la population des nématodes dans les racines, une augmentation de la croissance plagiotrope aux dépens de la croissance orthotrope et une production annuelle stable. La deuxième phase se caractérise par contre par une augmentation de l'infestation, une croissance orthotrope plus dominante et une alternance annuelle de la production des agrumes. L'intervention chimique à l'aldicarbe permet de réduire l'incidence des nématodes sur les agrumes, mais seuls les traitements appliqués au cours de la deuxième phase sont efficaces contre les nématodes.     

Biological control of the tick fowl Argas persicargas persicus by the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae

The pathogenicity of the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae against the tick fowl Argas persicargas persicus was studied. Bioassays revealed significant differences between the two fungi and the A. persicargas persicus stages exposed. The first nymphal instar was more highly susceptible to both fungi than the second nymphal instar. The unfed female of A. persicargas persicus was significantly less susceptible to both fungi than the engorged female. Application of M. anisopliae to sackcloth naturally infested with the tick fowl A. persicargas persicus induced mortality which reached 100?% three weeks after treatment under field conditions. The present study suggests that entomopathogenic fungi have good potential for tick fowl, A. persicargas persicus, control.     

Changes in fruit sugar concentrations in response to assimilate supply,metabolism and dilution: a modeling approach applied to peach fruit (Prunus persica)

The influence of assimilate supply, metabolism and dilution on sugar concentrations in the mesocarp of peach (Prunus persica (L.) Batsch) fruit during the main stage of fruit enlargement was analyzed with the SUGAR model of Génard and Souty (1996). The model predicts the partitioning of carbon into sucrose, sorbitol, glucose and fructose in the mesocarp of peach fruit. Based on measured data and the model, we determined values for the relative rates of sugar transformation. These rates were constant, varied with time or varied with relative fruit growth rate, depending on the type of sugar. Equations were derived to describe these rates and incorporated into the SUGAR model. The model simulated the effects of changing assimilate supply and fruit volume on sugar concentrations. The set of equations for the SUGAR model was rewritten to include the three components influencing sugar concentrations: assimilate supply, metabolism and dilution. The sugar types differed in sensitivity to these components. Sucrose was highly sensitive to changes in assimilate supply and to the dilution effect; it was not subject to intense metabolic transformation. Sorbitol was the most important carbohydrate in fruit metabolism, which explains why the sorbitol concentration was always low despite the strong positive effect of assimilate supply. The reducing sugars constituted a transitory storage pool and their concentrations were closely related to metabolism.     

Effects of timing of nitrogen fertilization on shoot development in peach (Prunus persica) trees

Shoot development was studied for two consecutive years in peach trees fertilized with N either in the previous fall or in the middle of the growing season. During the first year, two additional treatments were studied: no N supply and nitrate supplied in the irrigation water throughout the growing season. The number of shoots that developed depended on nitrogen availability in the period following bud break. During shoot development, leaf emergence occurred in one, two, or three stages, which ended at about 500 to 600 degree days, 1,000 to 1,200 degree days, and 1,500 to 2,000 degree days after bloom, respectively. The proportion of shoots exhibiting a second or third developmental stage depended on nitrogen availability at the beginning of that stage. Increasing nitrogen availability during a developmental stage prolonged the stage and increased the number of leaves produced.     

Apolipoprotein B-48 is the product of a messenger RNA with an organ-specific in-frame stop codon

The primary structure of human apolipoprotein (apo) B-48 has been deduced and shown by a combination of DNA excess hybridization, sequencing of tryptic peptides, cloned complementary DNAs, and intestinal messenger RNAs (mRNAs) to be the product of an intestinal mRNA with an in-frame UAA stop codon resulting from a C to U change in the codon CAA encoding Gln2153 in apoB-100 mRNA. The carboxyl-terminal Ile2152 of apoB-48 purified from chylous ascites fluid has apparently been cleaved from the initial translation product, leaving Met2151 as the new carboxyl-terminus. These data indicate that approximately 85% of the intestinal mRNAs terminate within approximately 0.1 to 1.0 kilobase downstream from the stop codon. The other approximately 15% have lengths similar to hepatic apoB-100 mRNA even though they have the same in-frame stop codon. The organ-specific introduction of a stop codon to a mRNA appears unprecedented and might have implications for cryptic polyadenylation signal recognition and RNA processing.     

Comparison of the adsorption of maize root mucilage and polygalacturonic acid on montmorillonite homoionic to divalent lead and cadmium

Summary Root mucilage material (RM) was isolated from maize plants grown in the field, and its affinity to montmorillonite (M) homoionic to Pb²⁺ and Cd²⁺ was compared with that of a commercial polygalacturonic acid (PGA). Adsorption isotherms of the commercial and natural materials on the two clay systems were compared in unbuffered systems at pH 3 and pH 6. Adsorption of PGA occurred only at pH 3, and was higher on M-Pb than on M-Cd. In contrast, the adsorption of RM was higher on M-Cd than on M-Pb. Total amounts of RM adsorbed at pH 3 were about 3 times lower on M-Cd and 20 times lower on M-Pb than the respective amounts of PGA adsorbed at the same pH. Polygalacturonic acid had a high content of relatively well dissociated (pKa = 3.5) carboxylic groups, and adsorbed on the clay surface at pH values lower than its pKa. At pH 6, the dissociation of the acid groups favoured its solubility, and the metal cations were then probably displaced by ion exchange. The lower affinity of RM to the clay materials was related to its average molecular weight, which was lower than that of PGA, and to its water solubility, which was higher than that of PGA. The low pH dependence of the adsorption of RM was related to its lower carboxylic acidity and higher content in hydroxyl and amino groups.     

Suppression of Meloidogyne javanica by Pseudomonas aeruginosa IE-6S in tomato: the influence of NaCl, oxygen and iron levels

Understanding the environmental factors that influence the suppression of disease-suppressive strains of Pseudomonas fluorescens is an essential step toward improving the level and reliability of their biocontrol activity. A 0.8 M NaCl concentration was optimal for in vitro survival and growth of IE-6S⁺ while, nematicidal activity by IE-6S⁺ was maximal when the bacterium was exposed to 0.4 M NaCl. The bacterium was highly sensitive to high (1.6 M) NaCl concentration. Culture filtrate of the bacterium resulting from the medium supplemented with 0.2 or 0.4 M NaCl showed the presence of secondary metabolite, hydrogen cyanide (HCN). Soil amendment with IE-6S⁺ alone or in conjunction with up to 0.8 M NaCl enhanced bacterial efficacy towards Meloidogyne javanica, the root-knot nematode. Soil amendment with NaCl up to 0.8 M also resulted in enhanced bacterial rhizosphere colonization and growth of tomato seedlings. Protein content of the shoot was reduced when soil was amended with 1.6 M NaCl. Inner root establishment of the bacterium was greatly affected in the soils treated with 1.6 M NaCl. Under in vitro conditions, IE-6S⁺ showed enhanced growth when kept at ambient oxygen conditions while the growth of bacterium affected when incubated at low oxygen conditions. Culture filtrate of the bacterium resulting from low oxygen level caused greater mortality of M. javanica juveniles in vitro compared with the filtrates obtained from ambient oxygen conditions. Culture filtrate from low oxygen conditions also showed the presence of hydrogen cyanide while those from ambient oxygen condition did not. Under glasshouse conditions, regardless of bacterial application, nematode penetration rate was greater when the pots were watered from the top; nematode penetration was lowered in bacterized pots compared with non-bacterized controls. IE-6S⁺ applied in the pots either watered from the top or bottom had no significant impact on growth of tomato but protein contents of the leaves increased after treatment with the bacterium. Rhizosphere and inner root colonization of the bacterium increased when the pots were watered from the top. Under in vitro conditions, with an increased iron concentration in the form of FeEDDHA, growth of IE-6S⁺ and its nematicidal activity increased. Culture filtrate of IE-6S⁺ obtained from liquid King's B medium supplemented with 0.5 or 1.0 mM FeEDDHA showed the presence of HCN. Under glasshouse conditions, soil treated with FeEDDHA alone did not reduce nematode penetration rates but did reduce greatly when applied in conjunction with IE-6S⁺. FeEDDHA applied at 0.5 mg/kg of soil in combination with IE-6S⁺ significantly enhanced plant growth and leaf protein contents. FeEDDHA at 1 mg/kg of soil increased bacterial populations both in the rhizosphere and inner root tissues of tomato.     

Determination of reference values for intraocular pressure and Schirmer tear test in clinically normal ostriches (Struthio camelus)

The purpose of this study was to establish normal physiologic reference values for intraocular pressure (IOP) and Schirmer tear test (STT) results in clinically normal ostriches (Struthio camelus). Twenty ostriches of both sexes, 10 juveniles (1.5-2 yr of age) and 10 adults, were included in this study. Complete ophthalmic examination was performed prior to this investigation. STT was performed by inserting a standard sterile STT strip over the ventral lid margin into the ventral conjunctival sac for 60 sec. Following the STT, IOP was measured using applanation tonometry with the Tono-Pen Vet tonometer after topical instillation of one drop of 0.5% proparacaine ophthalmic solution. The mean +/- SD and range of Tono-Pen readings of IOP for all birds was 18.8 +/- 3.5, with a range of 12-24. Mean IOP in juvenile ostriches was 19.7 +/- 3.6. Mean IOP in adult ostriches was 16.9 +/- 2.9. There was no statistically significant difference between young and adult birds (P = 0.07). The mean STT values in the present study were 16.3 +/- 2.5 mm/1 min when measurements from both eyes were averaged. Mean STT in juvenile and adult ostriches was 15.4 +/- 1.8 and 17.2 +/- 2.9 mm/1 min, respectively. There was no statistically significant difference between young and adult birds (P = 0.11). No statistically significant differences between genders were found for any of the results (P > or = 0.41). In conclusion, this study provides normal reference range values for STT and IOP in clinically healthy ostriches.     

Salinity tolerance of earthworms and effects of salinity and vermi amendments on growth of Sorghum bicolor

Salinity is a major factor limiting irrigated agriculture in arid regions. Vermi amendments can be used for improving the fertility of salt-affected soils. Current study was aimed to find out the response of different earthworm species to soil salinity and to check the effects of salinity and different vermi amendments on growth of Sorghum bicolor under salt stress. Eight earthworm species were subjected to different salinity levels for 4 weeks. Various vermi amendments and salinity treatments were provided in a factorial combination to S. bicolor plants to see their effect on growth and biomass parameters. L. mauritii, E. incommodus and P. posthuma were found to be the most salt-tolerant species showing good survival and growth till soil EC_e value of 10.48 mS cm^?1. Results showed that salinity significantly decreased plant growth that was enhanced by the application of different vermi amendments. Maximum growth of S. bicolor was recorded when vermicompost and vermiwash were used together under both saline and non-saline conditions. The results showed that the application of vermi amendments improved nutritional balance of the soil, delayed salt-induced damage to the plants and supported their growth so can be helpful in increasing crop production on saline soils.