Antagonistic Activity of Streptomyces thermocarboxydus to Fusarium oxysporum The cause of Leaf Rot Disease on Aloe vera (Aloe barbadensis Mill) in Bali, Indonesia

Aims: Aloe vera (Aloe barbadensis Miller) has been cultured in Bali, Indonesia since 2006. Its cultivation area is 170 ha including 5 regencies i.e. Buleleng, Karangasem, Bangli, Badung and Gianyar. This study was conducted to isolate and identify the Streptomyces sp. that potentially can be used to inhibit the growth of F. oxysporum and control the leaf rot disease on aloe vera with and to study the structural responses of F. oxysporum to the treatment of Streptomyces culture filtrate. Methodology and results: Samples were collected from Serokadan, Kerobokan, and Saba, Bali, Indonesia. The isolate of Streptomyces sp. that resulted in the highest antifungal activity was further observed on its morphological and ultrastructure characteristics using SEM and TEM. Identification was done by using 16S rRNA sequencing techniques. A greenhouse experiment was conducted to evaluate the effectiveness of the filtrate of Streptomyces sp. to control the leaf rot disease on aloe vera. The Streptomyces GYRRK was identified to be S. thermocarboxydus and the filtrate inhibited the growth of F. oxysporum by damaging cell wall and plasma membrane of macro conidia cell, micro conidia, and hypha. Treatment with the filtrate of S. thermocarboxydus with four sprays (one spray equal to 0.5 mL) over inoculated leaves of aloe vera reduced the leaf rot disease by 68%. Conclusion, significance and impact of study: This result suggests that filtrate of S. thermocarboxydus potentially can be used as an alternative control agent against leaf rot disease on aloe vera in Bali. Keywords: Aloe vera, Fusarium oxysporum, leaf rot disease, Streptomyces thermocarboxydus