Isolation of highly pathogenic pathogens and identification of formae speciales of Rehmannia glutinosa L.

Rehmannia glutinosa is an important medicinal plant in China that requires 8 10 years plastochrone for replanting, making it almost impossible for continuous cropping. Previous studies had shown that soil-borne diseases caused by microbial imbalance in rhizosphere microecology were the main obstacles to continuous cropping of R. glutinosa. However, little has been reported on the identification of formae speciales of R. glutinosa. Thus this study used the PDA-plate method after microscopic identification and analysis of ITS fungi identification to successfully screen 31 strains of Fusarium from soil under continuous cropping of R. glutinosa. Pathogenic detection results showed that strain Fusarium moniliforme (No. RPP009), F. solani (No. CCS013), F. graminearum (No. CCS024), Monographella nivalis (No. CCS038) and F. oxysporum (No. CCS043) were highly pathogenic. These strains severely decreased the height (by 23.40%~30.20% compared with CK) and fresh weight (by 23.58%~38.94% compared with CK) of R. glutinosa seedlings within 3 days after inoculation, subsequently causing organ deformation and death after 2 weeks. Further host biotype identification test results showed that F. oxysporum (No. CCS043) and M. nivalis (No. CCS038) strains only infected R. glutinosa and not other materials used in the experiment. The leaves of lower part of disease plants repeatedly turned hydropenic at noon and eventually withered followed by plant death after 3 5 days. Microscopic examination showed that stem vascular system in diseased plants turned brown or duck which led to the disagglomeration of spongy tissues. Underground root tubers then eventually ducked and decayed. The preliminary analysis suggested that the two identified strains were formae speciales of R. glutinosa.