Secretion compounds from Brevibacillus sp. SUT47 promote spore propagation of Acaulospora tuberculata colonizing maize roots (Zea mays L. cultivar Suwan 5)

The substrate-based production system has been widely applied for farm arbuscular mycorrhizal fungi (AMF) inoculum production. Plant growth promoting rhizobacterium (PGPR), Brevibacillus sp. SUT47 has been discovered to promote AMF spore production when co-inoculating on maize roots. However, the application of whole cell bacteria may cause the adverse outcome with contamination of bacterial cells in AMF inoculum. In order to avoid the bacterial cell contamination, we attempted to develop a new methodology using the bacterial secretion compounds as an optional technique to promote AMF spore production in maize roots. Secretion compounds of strain SUT47 were concentrated by freeze-drying and co-inoculated with the spores of Acaulospora tuberculata on maize seedling. The results showed that the bacterial secretion compounds promoted AMF spore production. The highest number of spores was produced when 360 mg of concentrated secretion compounds were applied. In contrast, the significant reduction of spore number was found when the secretion compounds at the concentration higher than 360 mg were applied. These results indicate the production of AMF spore was responded to concentration of bacterial secretion compounds which possibly contain an effective substance to promote AMF spore propagation.