Isolation and Identification of Chitinolytic Bacteria as Biocontrol Agent of Pathogenic Fungi on Gold Silkworm Cocoon Cricula trifenestrata

ABSTRACT

Aims: Cricula trifenestrata is one of natural insects which has not been domesticated yet, thus called as the wild silkworm. C. trifenestrata is known as a silk producer which has high economic and market value. However, the fungi attack on C. trifenestrata cocoon decreased quality and quantity of silk yarn. Chitinolytic bacteria have a high potential as biological control against pathogenic fungi. This research aimed to isolate, select, characterize, and identify chitinolytic bacteria as pathogenic fungi growth inhibitors on C. trifenestrata cocoon. Methodology and results: Chitinolytic bacteria was isolated from the uninfected and infected cocoon while fungi was isolated from the uninfected cocoon. Inhibition test was conducted by Fokkema method and chitinase activity was measured by Spindler method. A total of 36 chitinolytic bacteria and 10 suspected pathogenic fungi isolates have been isolated. Fungal pathogenicity test showed that isolate CSAJ.2 was suspected as fungal pathogen. In vitro inhibition test indicated that chitinolytic bacteria isolate BSEP.3 could inhibit the growth of pathogenic fungi CSAJ.2 with percentage of inhibition 50%. Isolate BSEP.3 showed highest chitinase activity (5.11 U/mL) at the 15th h. It able to inhibit the growth of pathogenic fungi with percentage of inhibition of 47.5% and 46.25%, respectively. Conclusion, significance and impact of study Identification of bacteria targeted on 16S rRNA gene showed that isolate BSEP.3 had 98% identity with Bacillus amyloliquefaciens B5 while identification of fungi using ITS region of the rDNA showed that isolate CSAJ.2 had 100% identity with Trichoderma virens TV242. Chitinase crude extract was effective to be used as a biological control agent of T. virens CSAJ.2.