Peer M. Schenk

Rhizosphere bacteria can provide multiple benefits to plants, including increased nutrient supply, pathogen/disease control, and abiotic stress tolerance, but results from pot trials do not always translate to field conditions. This study tested whether rhizosphere biocontrol bacteria can also provide plant growth promotion and how benefits can be provided at a commercial farm. Commercial lettuce seeds and plants were treated with rhizosphere biocontrol bacteria Bacillus velezensis UQ9000N, B. amyloliquefaciens 33YE, Brevibacillus laterosporus 4YE, and Pseudomonas azotoformans UQ4510An. 33YE increased the head diameter, plant height, and fresh weight of the Green Moon cultivar, while 33YE, UQ4510An, and UQ9000N increased the fresh and dry weight of Liston, a more heat-tolerant cultivar, via a single seed treatment or repeat root treatments under nursery and field conditions across different inoculation schedules and growth stages. Significant growth promotion was also demonstrated when inoculating field plants after transplanting (in particular for 33YE). Applications of these microbial biostimulants to lettuce seeds or plantlets potentially enable earlier transplanting and earlier harvests. Repeat inoculations using irrigation water and long-lasting formulations may further advance the benefits of these biostimulants as microbial biofertilisers for plant growth promotions in the field.