Efficacy of beneficial microorganisms in inducing resistance of sugarcane against sugarcane white leaf disease

Abstract

White leaf disease in sugarcane, caused by phytoplasma, is a major factor contributing to yield and quality loss. Sugarcane infected with approximately 100 copies/µl of the pathogen is in the latent stage, during which asymptomatic. Inducing plant resistance is a strategy that enhances broad-spectrum disease tolerance, offering protection against various pathogens. The use of effective microorganisms is one promising approach to stimulate such resistance. This study aimed to induce resistance in sugarcane and reduce the impact of white leaf disease. The initial phytoplasma concentration in infected plants was approximately 158 copies/µl. After seven applications of beneficial bacterial treatments, phytoplasma increased at a significantly lower rate in the treatment groups. The lowest concentrations were observed in the group treated with Bacillus subtilis No.15 at 10⁸ cfu/ml (256.7 copies/µl), followed by Streptomyces No.8 at the same concentration (357.7 copies/µl), compared to the infected control (12,540 copies/µl). Moreover, soaking setts and spraying with PGPR-3 enhanced plant growth parameters, including plant height (22.30%), root number (60.73%), root length (97.68%), and chlorophyll content (97.68%). All of microbial treatments stimulated the production of biochemical markers associated with induced resistance, including hydrogen peroxide (35%), ascorbate peroxidase (90.8%), and guaiacol peroxidase (92.3%), while reducing the production of malondialdehyde (MDA) by 93.4%. Gene expression analysis revealed that PR6-4 was upregulated by 92.7% and PR10-11 by 92.5% in the B. subtilis No.15.