Isolation and identification of pathogenic fungi from soft rot tissue of Amorphophallus konjac corm

Abstract

Konjac (Amorphophallus konjac) is a horticultural plant with high nutritional and medicinal values. Soft rot is a severe disease in production of konjac and it is also the main factor restricting the development of the konjac industry. It has been reported that the soft rot of konjac is mainly caused by pathogenic bacteria (mainly including Pectobacterium aroidearum, P. carotovorum subsp. carotovorum, P. chrysanthemi and Enterobacter sp.), and there is rare reports on pathogenic fungi that cause konjac soft rot. In order to clarify the pathogenic types and infection characteristics of the soft rot in Qujing City, Yunnan Province, the diseased corms were collected for fungal isolation by tissue isolation methods. The isolated fungi were identified by morphological and molecular identification methods based on ITS and LSU sequence analyses, and pathogenicity was determined according to Koch's rule. The infection characteristic was analyzed by mixed inoculation using the identified pathogenic fungi and the pathogenic bacteria of konjac soft rot. The results were as follows: (1) Three species of Fusarium spp. (Fusarium concentricum, F. oxysporum and F. ambrosium), one species of Mucor sp., one species of Rhizopus sp., one species of Penicillium sp. and one species of Clonostachys sp. were identified. (2) Statistics analysis found that Fusarium concentricum had the highest relative abundance (45.45%). (3) Koch postulates tests showed that inoculation with F. concentricum caused obvious soft rot symptoms of konjac corms within three days. (4) In addition, mixed Pectobacterium aroidearum and Fusarium concentricum together inoculation promoted the disease development, and the weight of rotten tissue was significantly higher than that of single inoculation using F. concentricum or Pectobacterium aroidearum. Overall, these results indicate that konjac soft rot may be caused by a combination of fungus and bacterium infection. The results provide a theoretical reference for the prevention and management of konjac soft rot.

Keywords

• amorphophallus konjac
• soft rot
• pathogenic fungus
• phylogenetic analysis
• pathogenicity