The Metabolic Elicitors of the Pseudomonas fluorescens N 21.4 Strain as Effective Biotechnological Inoculants for the Cultivation of Blackberry

The current need to provide sufficient and quality food to a growing population is linked to the development of new agricultural techniques based on improving the resistance of crops against biotic and abiotic stress. Since the consumption of blackberry is becoming very popular for its benefits on human health and it is a crop with a lack of specific inoculants able to boost plant resistance, we looked for an efficient, affordable, and sustainable biotechnological inoculant made of metabolic elicitor molecules of the beneficial rhizobacterium Pseudomonas fluorescens N 21.4 to get a more stress-resilient crop. For this, we inoculated the live rhizobacterium as positive control, since its capacity to elicit blackberry secondary defensive metabolism has been previously demonstrated (Garcia-Seco et al. 2015), and its metabolic elicitors to commercial cultivars of blackberry (Rubus cv. Loch Ness). We measured stress markers such as photosynthetic parameters, oxidative stress enzymatic activity, pathogenesis-related proteins and polyphenolic composition of the leaves, and the bioactive content of the fruit in two stages of ripening.

Our results showed that the metabolic elicitor-inoculated plants were more prepared to cope with stress since higher values of photosynthesis were observed, as well as lower enzymatic activity and an activation of pathogenesis-related proteins. Furthermore, the leaves and the fruits of the inoculated plants showed an enhancement in the concentration of beneficial polyphenols, highlighting the increase in epicatechin (Martin-Rivilla et al. 2020). This would mean having better quality fruits and would revalorize the leaves pruning as a potential source of polyphenols, providing an added value to the crop while following the premises of the circular economy.

The elicitation of the blackberry secondary defensive metabolism therefore demonstrates metabolic elicitors’ capacity to reinforce plant immune system and to increase the synthesis of beneficial bioactives, and this work suggest them as effective and ecofriendly plant inoculants.