Rhizobacteria improve the germination and modify the phenolic compound profile of pepper (Capsicum annum L.)

Abstract

The percentage of germination and the vigor of seeds are major determinants for an efficient seedling production to successfully establishment a crop. Some Capsicum annuum germinate within a few days, but others take until 21 days. Pepper seeds have significant amounts of free and bound polyphenols that are modified during the germination process. Phenolic compounds are used by seed to scavenge free radicals, they can also work as signal compounds or they can be related to plant's defense participating in the induced systemic resistance (ISR). However, the effect of plant growth-promoting rhizobacteria (PGPR) on pepper seed germination and the changes on phenolic profile has not been examined. In this study, we evaluated the transformation of phenolic compounds during seed germination produced by the inoculation with native PGPR on pepper seeds germination. Five bacterial strains: Cellulosimicrobium 60I1, Ochrobactrum 53F, Enterobacter 64S1, Pseudomonas 42P4 and Azospirillum brasilense Az39 were investigated. Our results showed that seed inoculation enhanced significantly seed germination, seedling growth, root length, and diameter of pepper seedling. In addition, changes in the profile of free and bound phenolic compounds were observed in seeds inoculated with PGPR. The free phenolic compounds were higher in the seedling inoculated with 60I1, 42P4 or the consortium with respect to control. The phenolic acid increased in seed inoculated suggests an elicitation of phenylpropanoid pathway related to ISR. The free flavonoids, naringenin, and rutin were present in the control treatment, while they were not detectable in the inoculated treatments. These could be used as a carbon source by PGPR during the germination or converted into flavonols that could protect the plants under abiotic stress. The tyrosol was present in 60I1 and in 60I1+42P4 treatment. The most effective strains were Cellulosimicrobium 60I1 and Pseudomonas 42P4 that increased their potential when it was used together.