Different strategies to optimize the inoculation of potato plants with Methylobacterium sp. 2A

Abstract

A plant growth-promoting rhizobacteria (PGPR) belonging to the genus Methylobacterium was isolated from roots of potato plants. This PGPR, named Methylobacterium sp. 2A, enhanced the growth of Arabidopsis and potato in vitro plants exposed to salt conditions, antagonized plant pathogens and reduced disease symptoms in potato plants infected with Phytophthora infestans (Grossi et al., 2020). We aim to understand if the inoculation of Methylobacterium sp. 2A enhances plant defense in potato plants through an induced systemic resistance (ISR) or by direct antagonism with the pathogen. To this end, we employed three inoculation strategies using a suspension of Methylobacterium sp. 2A cells (0.05 OD 600 units in 0.85% NaCl) or only 0.85% NaCl (control): i) roots of plants grown in solid MS for 3 weeks were inoculated with 100 µl of the suspension. Inoculated plants and controls were multiplied three consecutivetimes using internodes from the upper portion of the plants and the presence of Methylobacterium was checked; ii) plants grown in solid MS for 3 weeks were transferred to liquid MS for 24 h and then roots were inoculated with 0.8 ml of the suspension and harvested at 3-, 10-, and 13-days post inoculation (dpi). The presence of Methylobacterium in the liquid media was checked; iii) plants grown in solid MS for 3 weeks were transferred to liquid MS for 24 h and then inoculated with 0.8 ml of the suspension. At 8 dpi, plants were transferred to pots and placed in the greenhouse. Two weeks later, Methylobacterium was recovered from a leaf extract of inoculated plants and plant growth was evaluated in each condition. Plants had a better fitness in hydroponics and the growth promotion was evident in inoculated plants. P. infestans infection assays will be conducted on plants inoculated using the three different strategies to evaluate ISR.