IMPACT OF PHYLLOSPHERE METHYLOBACTERIUM ON HOST RICE LANDRACES

Abstract

The genus Methylobacterium includes widespread plant-associated bacteria that dominate the plant phyllosphere (occupying leaf surfaces), consume plant-secreted methanol, and can produce plant growth promoting metabolites. However, despite the potential to increase agricultural productivity, their impact on host fitness in the natural environment is relatively poorly understood. Here, we conducted field experiments with three traditionally cultivated rice landraces from north eastern India. We inoculated seedlings with native vs. non-native phyllosphere Methylobacterium strains, finding significant impacts on plant growth and grain yield. However, these effects were variable: whereas some Methylobacterium isolates were beneficial for their host, others had no impact or were no more beneficial than the bacterial growth medium. Host plant benefits were not consistently associated with Methylobacterium colonization, altered phyllosphere microbiome composition, changes in early expression of plant stress response pathways, or bacterial auxin production. We provide the first clear demonstration of the benefits of phyllosphere Methylobacterium for rice yield under field conditions, and highlight the need for further analysis to understand the mechanisms underlying these benefits. Given that the host landrace-Methylobacterium relationship is not generalizable, future agricultural applications will require careful testing to identify coevolved host- bacterium pairs that may enhance the productivity of high-value rice varieties.