Seedling growth promotion and potential biocontrol against phytopathogenic Fusarium by native rhizospheric Pseudomonas spp. strains from Amarillo Zamorano maize landrace

Abstract

Maize is one of the most important staple crops around the word. In Mexico, Los Altos de Jalisco is an agricultural region with the highest production of maize with rainfed irrigation, an agronomic management based on the use of no longer sustainable agrochemicals, and sowing of coated seeds of different commercial origin. Nowadays, the microbiota associated to the rhizosphere of native landraces is considered a reservoir of microbial resources with the potential to promote plant growth and control diseases. With the aim to find ecofriendly and cost-effective alternatives that can reduce the use of agrochemicals at seed germination and seedling growth of maize crop in Los Altos de Jalisco, this study focused on the search of fluorescent Pseudomonas strains as germination and seedlings growth promoters and biocontrol agents of fusariosis in maize, and highlight the importance of Mexican maize landraces as natural reservoirs of plant growth-promoting microorganisms. Samples of rhizospheric soil and seeds were collected from ten maize landraces and a pure line. Pseudomonas and Fusarium strains were isolated and selected by its antagonistic and pathogenic potential, respectively. Pseudomonas strains were phylogenetically identified by a 16S rRNA gene analysis, and Fusarium strains by the phylogenetic analysis of ITS region. The potential of Pseudomonas strains to promote seed germination and seedling/plant growth was explored through metabolic profiles and bioassays to evaluate bacteria-plant-fungus interactions. A total of 57 Fusarium spp. strains were grouped into four different Fusarium species complexes and 14 fluorescent Pseudomonas strains were classified into four Pseudomonas fluorescens subgroups. Pseudomonas strains displayed plant growth promotion and biocontrol capacity by increasing 38%–66% the dry weight of maize seedlings (p < 0.05), 23%–63% growth-inhibition of different Fusarium strains in dual cultures, and a range of 4.5–20 inhibition score based on a rate scale when inoculated in seeds. Pseudomonas spp. metabolic profiles were diverse, but all the strains proved to be innocuous, and Pseudomonas sp. 4L, 10L and 11L showed desirable enzymatic capacities from an agrobiotechnological approach. Additionally, Pseudomonas sp. 4L increased germination and seedling growth of maize, by increasing 20–51% the number of germinated seeds, 16–38% the length of seedling aerial part, 30–140% seedling length of roots, 15–32% seedling fresh weight, and 21–33% seedling dry weight, and reduced 75–96% the damage generated by Fusarium spp. on naturally infected seeds. This study revealed that Pseudomonas sp. 4L and 11L are regional promising ecofriendly and cost-effective alternatives as adjuvants in the nutritional and phytosanitary management at seed germination and seedling growth of maize crop in Los Altos de Jalisco region, and highlight the importance of the rhizosphere microbiome of Mexican maize landrace as natural reservoir of plant growth-promoting microorganisms.