Promotion of the growth and yield of Zea mays by synthetic microbial communities from Jala maize

Abstract

Plant growth-promoting bacteria (PGPB) are a source of nutrient supply, stimulate plant growth, and even act in the biocontrol of phytopathogens. However, these phenotypic traits have rarely been explored in culturable bacteria from native maize landraces. In this study, synthetic microbial communities (SynCom) were assembled with a set of PGPB isolated from the Jala maize landrace, some of them with additional abilities for the biocontrol of phytopathogenic fungi and the stimulation of plant-induced systemic resistance (ISR). Three SynCom were designed considering the phenotypic traits of bacterial strains, including Achromobacter xylosoxidans Z2K8, Burkholderia sp. Z1AL11, Klebsiella variicola R3J3HD7, Kosakonia pseudosacchari Z2WD1, Pantoea ananatis E2HD8, Pantoea sp. E2AD2, Phytobacter diazotrophicus Z2WL1, Pseudomonas protegens E1BL2, and P. protegens E2HL9. Plant growth promotion in gnotobiotic and greenhouse seedlings assays was performed with Conejo landrace; meanwhile, open field tests were carried out on hybrid CPL9105W maize. In all experimental models, a significant promotion of plant growth was observed. In gnotobiotic assays, the roots and shoot length of the maize seedlings increased 4.2 and 3.0 times, respectively, compared to the untreated control. Similarly, the sizes and weights of the roots and shoots of the plants increased significantly in the greenhouse assays. In the open field assay performed with hybrid CPL9105W maize, the yield increased from 11 tons/ha for the control to 16 tons/ha inoculated with SynCom 3. In addition, the incidence of rust fungal infections decreased significantly from 12.5% in the control to 8% in the treatment with SynCom 3. All SynCom designs promoted the growth of maize in all assays. However, SynCom 3 formulated with A. xylosoxidans Z2K8, Burkholderia sp. Z1AL11, K. variicola R3J3HD7, P. ananatis E2HD8, P. diazotrophicus Z2WL1, and P. protegens E1BL2 displayed the best results for promoting plant growth, their yield, and the inhibition of fungal rust. This study demonstrated the biotechnological eco-friendly plant growth-promoting potential of SynCom assemblies with culturable bacteria from native maize landraces for more sustainable and economic agriculture.

Keywords: Jala maize; biocontrol; endophytic bacteria; induced systemic resistance (ISR); plant growth-promoting bacteria (PGPB); plant-microbe interaction; synthetic microbial communities (SynCom).

Figure 1

Functional traits of Jala maize endophytes individually and in the synthetic microbial communities (SynCom). The growth promotion and biocontrol (A) capabilities of each of the studied isolates are shown and compared with (B) the formulated SynCom. The colors represent the absence and presence of these activities as well as statistically significant differences according to Duncan's test (^*P ≤ 0.05, ^**P ≤ 0.01, and ^***P ≤ 0.001).

Figure 2

Heat map of the fungal radial growth inhibition by endophytic bacteria. (A) Fusarium oxysporum, (B) Pestalotia sp., (C) Curvularia sp., (D) Colletotrichum sp., and (E) Helminthosporium sp.

Figure 3

Enzymatic activity of maize roots' phenylalanine ammonium lyase (PAL) treated with inoculants; the P. protegens E1BL2 strain was used as a control. The PAL activity of inoculated and uninoculated plants was compared using Tukey's test (*p ≤ 0.05).

Figure 4

Effect of the inoculation of SynCom on the shoot, root length, and weight of the Conejo landrace. (A) Application of SynCom bioinoculants on the gnotobiotic system and (B) greenhouse system. Tukey's test compared the lengths and weights of inoculated and uninoculated plants (*p ≤ 0.05).

Figure 5

Phenotypic traits of Jala maize SynCom. (A) Quantitative metallophore test in a liquid medium, blue colors represent low production, and green and yellow colors represent high production. (B) In quantitative IAA determination, yellow colors represent low production, and orange and red colors represent high production. (C) In quantitative phosphate solubilization, the intensity of the blue color is proportional to the production of orthophosphate. (D) Metallophore production test in plates, the size of the halos was determined to estimate the production of each particular metallophore. (E) Inhibition of mycelial growth of Pestalotia sp. by SynCom 3. (F) Inhibition of mycelial growth of Colletotrichum sp. by SynCom 3. (G) Plant growth promotion assay in a gnotobiotic system by SynCom. (H) Plant growth promotion in a greenhouse system by SynCom.

Figure 6

Field test of bacterial SynCom application in maize crop using the commercial hybrid CPL9105W. (A) Geographic localization of the open field in Mixquiahula Hidalgo, Mexico (20.192457,−99.243521). (B) Bacterial SynCom effect in the crop yield (ton/ha). (C) Bacterial SynCom effect in the rust incidence percentage (%). (D) A comparison of untreated control plants and SynCom 3 treatment. (E) Ears or maize without treatment and (F) ears treated with SynCom 3. The test was conducted in the experimental fields from the Innovation and Technological Development Center Mezquital Valley, Mixquiahula Hidalgo, México. Tukey's test compared the yield and rust incidence of inoculated and uninoculated plants (*p ≤ 0.05).