Converter slag causes gradual collapse of chlamydospore of the rice false smut fungus and suppresses hyphal invasion into rice roots

Abstract

Abstract The rice false smut disease has become a serious threat to rice production. Chlamydospores are the primary durable inoculum for this disease in paddy soil. Recently, mixing converter slag into paddy soil has been shown to decrease the occurrence of the disease; however, the mechanism underlying this suppression is unknown. To confirm the disease suppression, firstly we conducted the converter slag application test (3t/ha) in a paddy field. Next, we investigated the effects of converter slag-added solution (CSS), neutralized CSS (NCSS), and converter slag-added soil extract (CSSE), which corresponds to 3t/ha application of the converter slag in a paddy field, on chlamydospore morphology and germination, as well as the effect of CSSE on hyphal invasion of rice roots by germinated chlamydospores. The field test showed 75.6% suppression of the disease occurrence. Moreover, in the CSS test, the normal chlamydospores rapidly became transparent and gradually collapsed. In contrast, NCSS slowed chlamydospore collapse. The abnormal germination percentages in CSS were higher than those in NCSS. The percentages of transparent, collapsed, and normally germinated chlamydospores obtained in CSSE were intermediate between those obtained in CSS and NCSS. This suppression may have been due to the soil buffering effect. Furthermore, hyphal invasion by germinated chlamydospores into rice roots in CSSE was suppressed compared to that in control. These results suggest a gradual collapse caused by the cation may be suppressed by the anion, and subsequent infection of the rice roots may be inactivated. These mechanisms may be contributed to the disease suppression in fields.