Production of pectinases and cellulase by six Pythium species isolated from necrotic strawberry roots
Polygalacturonase and polymethylgalacturonase activity was detected in filtrates ofPythium irregulare, P. perniciosum, P. sylvaticum, andP. dissotocum but not in filtrates ofP. rostratum andP. acanthicum. OnlyP. irregulare, P. perniciosum andP. dissotocum elaborated pectin methyl esterase and in trace amounts. None of the species produced detectable pectintrans-eliminase and “macerating enzyme” activity.P. sylvaticum was the only species of four tested which produced cellulase.
Induction of hydrolytic enzymes of phytopathogenic fungi in response to Trichoderma viride influence biocontrol activity
Soil borne fungal phytopathogens like Pythium,Fusarium,Alternaria,Aspergillus,B otrytis, Rhizoctonia and Phytophthora cause both post and pre harvest pathologies in agricultural crops (Chet & Inbar, 1994).Traditional pesticides, fungicides and fumigants have drastic effects on the environment in terms of pollution and toxicity.The generation of resistant strains due to the repeated application of these fungicides also offers serious challenges (Naseby, Pascual, & Lynch, 2001). As an advent to resist ecological impacts of chemical pesticides and fertilizers an array of biocontrol agents and biofertilizers including bacteria such as Bacillus subtilis ISSN: 2319-7706 Volume 3 Number 9 (2014) pp. 1207-1217 http://www.ijcmas.com
Effect of stress conditions on collapse deformation behavior of a rockfill material
A set of saturated and dry-saturated large-scale triaxial tests were conducted in order to explore the effects of stress conditions on the saturation-induced collapse deformation behavior of a rockfill material. Specimens were tested in different confining pressures and for dry-saturated tests the specimens were submerged in various shear stress levels. The results indicate that in all of the dry-saturated tests a sudden reduction in the volume of the specimens was observed during the submerging process. The ratio of the minimum axial strength of a submerged specimen (at the end of the saturation process) to the shear strength of the specimen before saturation is defined as the coefficient of stress recovery, Csr. Results of the dry-saturated tests showed that this ratio increases as the confining pressure increases and decreases by increasing the shear stress level. According to the results of dry-saturated tests the values of internal friction angle reduction caused by saturation (Δϕc), the ratio of the elasticity modulus of the material after saturation to its elasticity modulus in dry condition, i.e., Ewet/Edry, and also the saturation induced sudden volumetric strain (εvc) decrease as the confining pressure increases. However the shear stress level does not have any meaningful effect on the variation of Dfc, Ewet/Edry and (εvc).