Biological activity of Paenibacillus polymyxa GT2 isolate from soil in Japan against anthracnose caused by Colletotrichum orbiculare in cucumber

Cucumber anthracnose is a destructive fungal disease caused by <i>Colletotrichum orbiculare</i>. Common control strategies include chemical fungicides. However, this can lead to the development of pathogenic resistance. Therefore, it is necessary to identify natural compounds or microorganisms to develop new chemicals and the biological control of fungal pathogens. Isolate GT2, a bacterial isolate from soil samples collected in Shimane Prefecture, Japan, significantly inhibited <i>in vitro</i> mycelial growth and conidial germination of <i>C. orbiculare</i>, indicating a fungicidal effect against this pathogen. Furthermore, anthracnose lesion formation was significantly suppressed without phytotoxicity when cucumber leaves were pretreated with a cell culture suspension of the isolate GT2 before inoculation with <i>C.orbiculare</i>. Bioautography of the culture filtrate (CF) of the isolate GT2 using thin-layer chromatography showed that the compound inhibiting <i>C. orbiculare </i>growth had an Rf value of 0.38. The effective compound in GT2-CF was ethyl acetate insoluble and heat-stable at 121 C and has a molecular weight larger than 1 000 Da. In conclusion, <i>Paenibacillus polymyxa</i> GT2 demonstrated the potential for developing a new fungicide and biological agent against anthracnose disease caused by <i>C. orbiculare</i>.