Ochrobactrum cytisi IPA7.2 promotes growth of potato microplants and is resistant to abiotic stress.

Bacteria in natural associations with agricultural crops are promising for use in the improvement of clonal micropropagation of plants. We clarified the taxonomic position of Ochrobactrum cytisi strain IPA7.2 and investigated its tolerance for salinity, high temperature, and glyphosate pollution. We also tested the strain's potential to promote the growth of potato (Solanum tuberosum L.) microplants. Using the IPA7.2 draft genome (no. NZ_MOEC00000000), we searched for housekeeping genes and also for the target genes encoding glyphosate tolerance and plant-growth-promoting ability. A multilocus sequence analysis of the gap, rpoB, dnaK, trpE, aroC, and recA housekeeping genes led us to identify isolate IPA7.2 as O. cytisi. The strain tolerated temperatures up to 50 °C and NaCl concentrations up to 3-4%, and it produced 8 µg ml-1 of indole-3-acetic acid. It also tolerated 6 mM glyphosate owing to the presence of type II 5-enolpyruvylshikimate-3-phosphate synthase. Finally, it was able to colonize the roots and tissues of potato microplants, an ability preserved by several generations after subculturing. We identified the development phase of potato microplants that was optimal for inoculation with O. cytisi IPA7.2. Inoculation of in vitro-grown 15-day-old microplants increased the mitotic index of root meristem cells (by 50%), the length of shoots (by 34%), the number of leaves (by 7%), and the number of roots (by 16%). Under ex vitro conditions, the inoculated plants had a greater leaf area (by 77%) and greater shoot and root dry weight (by 84 and 61%, respectively) than did the control plants. We recommend O. cytisi IPA 7.2 for use in the growing of potato microplants to improve the production of elite seed material.