Potential of Herbaspirillum and Azospirillum Consortium to Promote Growth of Perennial Ryegrass under Water Deficit

Abstract

Plant growth-promoting bacteria (PGPB) can mitigate the effect of abiotic stresses on plant growth and development; however, the degree of plant response is host-specific. The present study aimed to assess the growth-promoting effect of Herbaspirillum (AP21, AP02), Azospirillum (D7), and Pseudomonas (N7) strains (single and co-inoculated) in perennial ryegrass plants subjected to drought. The plants were grown under controlled conditions and subjected to water deficit for 10 days. A significant increase of approximately 30% in dry biomass production was observed using three co-inoculation combinations (p < 0.01). Genomic analysis enabled the detection of representative genes associated with plant colonization and growth promotion. In vitro tests revealed that all the strains could produce indolic compounds and exopolysaccharides and suggested that they could promote plant growth via volatile organic compounds. Co-inoculations mostly decreased the in vitro-tested growth-promoting traits; however, the co-inoculation of Herbaspirillum sp. AP21 and Azospirillum brasilense D7 resulted in the highest indolic compound production (p < 0.05). Although the Azospirillum strain showed the highest potential in the in vitro and in silico tests, the plants responded better when PGPB were co-inoculated, demonstrating the importance of integrating in silico, in vitro, and in vivo assessment results when selecting PGPB to mitigate drought stress.

Endophytic PGPB Improves Plant Growth and Quality, and Modulates the Bacterial Community of an Intercropping System

“…This shift indeed correlated with an improvement in the growth and quality of the intercropping system, as seen in other studies (Wang et al, 2018;Zhong et al, 2019;Estrada-Bonilla et al, 2021). The capacity of these microbes to colonize the plant tissue (Cortés-Patiño et al, 2021), potentially ensures that the mutualist relationship between microbes and FIGURE 5 | Inoculation of the intercropping system with Herbaspirillum sp. AP21 brought about changes in the microbial community, which positively correlated with an increase in plant growth and quality.…”

“…Inoculation with AP21 at 50% N, for instance, phenocopied the 100% N chemical control in terms of biomass, total N content, and crude protein. This positive effect of the inoculants is likely to be a direct consequence of microbial N fixation, as both microbes are diazotrophs, or an indirect effect due to their capacity to synthesize phytohormones or produce ACC deaminase activity (Cortés-Patiño et al, 2021). The positive effect of these microbes on plant growth and nutrition has been previously seen in other crops.…”

“…Previously, we demonstrated the PGPB potential of two endophytes to promote the growth of both perennial ryegrass and red clover under drought and phosphorus limitation (Cortés-Patiño et al, 2021;Santos-Torres et al, 2021). Here, we further explored the PGPB potential of these two bacterial endophytes to facilitate the growth of an intercropping system conformed by both perennial ryegrass and red clover.…”

“…AP21 (SAMN15498633) and Azospirillum brasilense D7 (SAMN16830199) were provided by the Microorganism Germoplasm Collection of Agrosavia, Colombia. These strains were previously identified by whole genome sequencing and were characterized as facultative endophytes (Cortés-Patiño et al, 2021). For routine experiments, these strains were grown in DYGS culture medium, incubated at 30 • C, and agitated at 140 rpm for 48 h (Baldani et al, 2014).…”

“…Likewise, Herbaspirillum, can increase the biomass production of pastures in low-fertility soils without using N fertilization (Marques et al, 2017). Inoculation with Herbaspirillum also increased the biomass of Miscanthus sinensis and perennial ryegrass plants (Straub et al, 2013;Cortés-Patiño et al, 2021).…”