Caragana species are woody legumes widely distributed in the arid regions of China. These plants form root nodules but their nodule bacteria have not been clearly classified. A total of 112 symbiotic bacterial isolates were obtained from four Caragana species grown in Liaoning Province and were characterized with ARDRA, sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins, BOX-PCR and sequencing of the 16S rRNA gene. Most of them were classified as Mesorhizobium belonging to 11 putative species. Three isolates were identified as Rhizobium etli and Burkholderia spp. This study offers new information about the Caragana-rhizobia association and resource for selection of inoculants used in sustainable agriculture and for further studies on the Caragana rhizobia.
Rhizoctonia solani causes the disease peanut sheath blight, involving symptoms of maceration and necrosis of infected tissue, mainly caused by cell-wall-degrading enzymes (CWDEs). This study investigated the production of CWDEs including polygalacturonase (PG), polymethyl-galacturonase (PMG), cellulase (Cx) and β-glucosidase by R. solani in vitro (in liquid culture) and in vivo (in peanut plants). Significant PG, PMG, Cx and β-glucosidase activities were detected in infected tissues including stalk and leaves of Baisha and Silihong peanut cultivars. Extracts of healthy tissue showed little or no such activities. In shaken liquid cultures of R. solani in medium containing pectin or pectin plus carboxymethyl cellulose (CMC) as the carbon source(s), PG and PMG were notably active. Significant Cx activity was detected in cultures with CMC or pectin plus CMC as the carbon source(s). However, only a very low level of β-glucosidase activity was observed in cultures with any of the tested carbon sources. An increase of pH was recorded in decayed peanut tissues and liquid culture filtrates; the filtrate pH and fungal growth positively correlated. The fungal growth and/or pH were important factors for the production of PG, PMG and Cx in culture with pectin plus CMC as the carbon source. A single active PG isozyme with isoelectric point around 9.2 was detected in culture filtrates and in infected peanut tissues by the method of isoelectric focusing electrophoresis. The crude enzymes extracted from liquid culture of R. solani induced decay of healthy peanut leaves.
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