Evaluation of low-cost carbon sources in anaerobic soil disinfestation in suppression of Rhizoctonia root rot in bean

Anaerobic soil disinfestation (ASD) is a pre-plant soil rehabilitation method used to control soilborne diseases. However, the high cost of carbon sources remains a major constraint for the wider adoption of ASD in commercial fields. Therefore, the present study was conducted to identify low-cost carbon source alternatives for ASD to manage Rhizoctonia root rot (RRR) in beans in Nepal. The experiment was conducted in a randomized complete block design with eight replications and ten carbon source treatments. The treatments included two non-amended controls (covered; anaerobic and uncovered; anaerobic), two oil cakes (butter tree and neem), four plant biomasses (water hyacinth, nettle leaves, banana pseudostem, and Eupatorium sp.), and two standard carbon sources (rice bran and molasses). Rhizoctonia solani inoculum and carbon sources were incorporated into soil in pots, irrigated to saturation, sealed with plastic bags for three weeks to induce anaerobic conditions, and then uncovered for seven days before sowing bean seeds. Then the plants were uprooted and washed with tap water, and RRR severity, incidence, root and shoot length and plant biomass were recorded. Rhizoctonia root rot severity was significantly lower in bean seedlings grown in ASD-treated soils amended with banana pseudostem, rice bran, and molasses compared with seedlings grown in both non-amended controls. Overall, amendments with rice bran, molasses, and banana pseudostem resulted in the lowest disease severity. Disease severity was reduced by 19.2–38.6% relative to the aerobic control. The greatest reduction (38.6%) was observed in bean seedlings grown in ASD-treated soil amended with banana pseudostem and rice bran, followed by molasses-amended ASD soil, which showed a 38% reduction compared with the aerobic control. Banana pseudostem, an almost freely available carbon source that performed comparably to standard carbon sources such as rice bran and molasses, offers a compelling opportunity to broaden the adoption of anaerobic soil disinfestation (ASD) for effective soilborne disease management. Therefore, these results indicate that banana pseudostem biomass could serve as a low-cost alternative carbon source for the sustainable management of soilborne diseases in Nepal.