Rhizosphere transplants from Guinea grass support the yield and modulate the microbiota of chili and rice root systems depending on the plant's variety and growth stage

Biofertilization by rhizosphere microbiome transplant (RMT) is an emerging approach of plant microbiome engineering, for its potential to reduce the input of synthetic chemicals, hence preserving soil ecosystem and human health. However, its feasibility and outcomes need deeper investigation through field studies. This work aimed at evaluating the efficacy and the ecological impact on soil microorganisms of a biofertilizer that could be self-produced by farmers in Sri Lanka through RMT from Guinea grass (Panicum maximum), a widespread weed able to adapt to harsh conditions. Root wash (RW) and arbuscular mycorrhizae (AMF) obtained from the root system of Panicum were separately supplied to chili pepper and two local varieties of rice, Suwadel and Kuruluthuda. Decreasing doses of chemical fertilizer were also applied, combined with the inocula or as separate controls. In chili and in rice var. Suwadel all the biofertilization treatments improved the crop productivity compared to the non-treated controls or to the plants supplemented only with the minimum dose of chemical fertilizer. RW and AMF applied alone or supplied with 50 % of the optimal fertilizer dose resulted in yields comparable to 100 % chemical fertilization, suggesting the potential to reduce its input by half. Microbiome transplant showed an impact on bacterial and fungal communities at flowering stage, with the enrichment of Bacillaceae, Exiguobacteraceae, Micrococcaceae, Trichocomaceae and Aspergillaceae compared to non-treated plants. Our results indicate promising results of RMT in terms of crop yield improvement in field conditions, with structural changes in the rhizosphere microbiome related to the recruitment of beneficial microorganisms.