Lettuce Production under Reduced Levels of N-fertilizer in the Presence of Plant Growth-promoting Bacillus spp. Bacteria

Lettuce consumption has increased worldwide due to the recognition of its nutritional value and to the consumers’ search for healthier foods. Increased consumption must be coupled with more efficient production, demanding more nutrients. However, the utilization of chemical inputs in horticulture is decreasing, and biological approaches, such as the inoculation with plant growth-promoting bacteria (PGPB), are becoming more popular. Species of Bacillus have long been known promote the growth of plants, including lettuce, in agricultural soils, but little is known about their potential under Brazilian conditions. We have tested the ability of B. subtilis, B. pumilus, and B. amyloliquefaciens, carried in single or combined pre-commercial inoculants, to act as PGPB for field-grown lettuce plants of cultivar Elisa. In our experiments, the PGPB were challenged to promote plant growth when the recommended dose of nitrogen (N) fertilizer was reduced by 50%. Our results demonstrated that all species, either alone or combined, were able to improve plant vigor, the number of leaves, and the average diameter and weight of the lettuce heads, under the test conditions. Average gains in plant vigor and head weight due to all species were of the order of 50% relative to the control (no N fertilizer) treatment and, in most cases, gains due to the presence of the bacteria were superior to those promoted by the full (100%) N fertilization. This is the first report of positive utilization of pre-commercial products containing Bacillus for lettuce growth in Brazil