1. Investigación

Two plant growth promoting rhizobacteria (PGPR) were tested to evaluate their capacity to prime rice seedlings against stress challenge (salt and Xanthomonas campestris infection). As is accepted that plants respond to biotic and abiotic stresses by generation of reactive oxygen species (ROS), enzyme activities related to oxidative stress (ascorbate peroxidase (APX, EC 1.11.1.11), guaiacol peroxidase (GPX, EC 1.11.1.7), glutathione reductase (GR, EC 1.6.4.2) and superoxide dismutase (SOD, EC 1.15.1.1)) as well as the pathogenesis-related proteins (PRs) ß-1,3-glucanase (PR2, EC 3.2.1.6) and chitinase (PR3, EC 3.2.1.14) weremeasured at 3 timepoints after stress challenge.Inaddition,photosyntheticparameters related with fluorescence emission of photosystem II (F0, Fv/Fm, PSII and NPQ) were also measured although they were barely affected. Both strains were able to protect rice seedlings against salt stress. AMG272 reduced the salt symptoms over 47% with regard to control, and L81 over 90%. Upon pathogen challenge, 90% protection was achieved by both strains.All enzyme activities related to oxidative stress were modified by the two PGPR, especially APX and SOD upon salinity stress challenge, and APX and GR upon pathogen presence. Both bacteria induced chitinase activity 24 and 48 h after pathogen inoculation, and L81 induced ß-1,3-Glucanase activity 48 h after pathogen inoculation, evidencing the priming effect. These results indicate that these strains could be used as bio-fortifying agents in biotechnological inoculants in order to reduce the effects of different stresses, and indirectly reduce the use of agrochemicals.

Beneficial rhizobacterium Pseudomonas fluorescens N 21.4 and its metabolic elicitors inoculated to cultivars of blackberry (Rubus spp. Var. Loch Ness) reinforced the plants’ immune system and improved their fitness by increasing photosynthesis, decreasing oxidative stress, and activating pathogenesis-related proteins. They also triggered the leaves’ flavonoid metabolism, enhancing the accumulation of beneficial phenolic compounds such as kaempferols and quercetin derivatives. The elicitation of leaf secondary metabolism allows one to take advantage of the blackberry leaves (a current crop waste), following the premises of the circular economy, to isolate and obtain high added value compounds. The results of this work suggest the use of N 21.4 and/or its metabolic elicitors as plant inoculants as an effective and economically and environmentally friendly agronomic alternative practice in the exploitation of blackberry crops to obtain plants with a better immune system and to revalorize the leaf pruning as a potential source of polyphenols.