Disease suppression by pre-treatment with bio-sulfur on cucumber leaves inoculated with Colletotrichum orbiculare

Abstract

Bio-sulfur is one of by-product of sulfur that produced as a result in process of desulfurization from a landfill site. In Europe, it is called 'Bio-sulfur' because microorganism such as Thiobacillus sp. collected as sulfur element. Many researches have illustrated that some sulfuric materials have an effect on growth of mycelium and disease suppression by fungus. But, they can cause some phytotoxicities on young leaves in eco-friendly orchards because of its high pH. Compare with other sulfuric materials, bio-sulfur has lower pH also the small particle is advantageous to suppress the fungal disease like powdery mildew. So, in this study, in order to investigate the practical use of bio-sulfur as an agent for controlling of plant disease, antifungal activity of bio-sulfur was tested in vitro against Colletotrichum orbiculare. Efficacy of bio-sulfur for suppressing disease severity was evaluated in vivo, against the anthracnose disease too. Mycelial growth of C. orbiculare was inhibited on the agar medium containing bio-sulfur. To extent contact area between bio-sulfur and pathogen, C. orbiculare was inoculated in the broth medium containing bio-sulfur. As a result, fresh and dry weight of mycelium decreased in broth medium added bio-sulfur. Also, the disease severity on the leaves pre-treated with bio-sulfur was significantly decreased compared to those of untreated one. To understand how the anthracnose disease is suppressed by bio-sulfur, the infection structure of C. orbiculare on the cucumber leaves was observed using a fluorescent microscope. Appressorium is a specific mechanism of some fungus including C. orbiculare for invasion into plants. There were only a few of appressoria on the cucumber leaves pre-treated with bio-sulfur whereas abundant appressoria were observed on untreated one. Also, similar results of bio-sulfur were observed on the leaves pre-treated with a commercial fungicide Benomyl®. Based on these results, it is suggested that the inhibition of appressorium formation by bio-sulfur may be the main cause of anthracnose suppression on cucumber leaves. These results may be useful for plant protection especially in eco-friend farms where application with commercial chemicals are limited.