Cell Wall Degrading Enzymes Produced by Rhizoctonia solani and Their Pathogenicity to Rice Plants

Abstract

The cell wall degrading enzymes(CWDEs) such as polygalacturonase(PG),cellulase(Cx),pectin methylgalacturonase(PMG),polygalacturonic acid trans-eliminase(PGTE) and pectin methyl trans-eliminase(PMTE) were produced in improved Marcus′s medium by Rhizoctonia solani Kuhn causing rice sheath blight.Among five CWDEs,PG,Cx and PMG were significantly higher in the activity than PGTE and PMTE.The culture conditions for the CWDE production of the pathogen were studied.It was appropriate to the CWDE production for the pathogen to be cultured in improved(Marcus′s) medium(pH5) at 28 ℃ without shaking for six days.In addition,the pathogen could produce the CWGEs mentioned above in the lesion after inoculated to rice sheath.There were obvious differences in CWDE activity among three parts of the lesion such as outer chlorotic part,brown part and central dead part.The CWDE activity in the outer chlorotic part was the highest,which was about 3.4 times as much as that of control(healthy part).The next was the CWDE activity in the brown part,which was about 2.9 times as much as that of control.The CWDE activity in the central dead part was the lowest,but which was significantly higher than that of control.These results suggested that the CWDEs produced by the pathogen play an important role in lesion formation and expansion.The pectinase(PG,PMG) and cellulase(Cx) could damage the cell membrane of rice sheath and macerate the sheath tissue through single enzyme or mixed enzyme treatment.