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Isolation and identification of Cordyceps cateniobliqua Bm1 and its pathogenicity on the silkworm, Bombyx mori

Guanyu Zhu^a,?, Ping He^a,?, Yu Li^a, Mingzhen Ma^a, Ying Chen^a, Yong Chena , Fuzhen Sun^a, Yiling Zhang^a,b, Qiang Wang^a,b, Zhongyuan Shena,b,?

 
ABSTRACT:     Silkworm?s fungal infection is a kind of communicable diseases caused by parasitic fungi. In this study, a rare fungal Bm1 strain was isolated from infected silkworms in cocoon production in Zhenjiang city, China. The result from morphological investigation showed that the conidiogenous cells of the isolated fungal strain had flask-like phialides with slightly swollen or columnar bases. Most of the conidia were oval and arranged in a broadly ?V?-like manner that resulted in irregularly curved chains. The color of the fungal colony was white at the initial growing stage and gradually became pink. The average hyphal growth rate of the strain was 3.42?1.24 mm/d on the PDA solid medium. Phylogenetic analysis showed that the Bm1 strain was clustered in the same clade with Isaria cateniobliqua, Cordyceps cateniobliqua, and Evlachovaea kintrischica. Combining the morphological characteristics with rRNA-ITS sequence, this newly isolated fungal strain was identified as a C. cateniobliqua strain, named as C. cateniobliqua Bm1. The C. cateniobliqua Bm1 could infect the silkworm through contacting transmission, and the course of this disease was about 5 to 19 d. The mortality rates of the silkworm caused by infection of C. cateniobliqua Bm1 positively increased with the concentration of inoculated conidial suspension. The estimated LC50 value was 1.18 ? 109 conidia/ml, a low pathogenicity to the silkworm compared with the Beauveria bassiana.

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* Corresponding author, E-mail: szysri@163.com

Received 7 May 2021, Accepted 29 Sep 2021