Using microbes as biostimulants: endophytic Pseudomonas spp. from Agave palmeri promotes crop growth by participating in the rhizophagy cycle and inhibiting fungal growth
Creators: name: Zhang, Qiuwei
Publisher: name: No Publisher Supplied
Year: 2023

description: Overuse of chemical fertilizers and pesticides in agriculture has led to vast environmental damage via chemical leeching and off-target effects. In response, the agriculture industry is starting to turn to biological agents, such as beneficial microbes, to combat nutrient deficiencies and pathogen infections. Beneficial microbes can be obtained from a variety of sources, one of which is from the plants themselves. Endophytes, defined as microbes that live inside plant tissues without causing harm, are potential candidates for environmentally friendly alternatives to agrochemicals due to their ability to enhance growth and induce pathogen resistance in a variety of hosts. While there are many potential sources of endophytes, one overlooked source is wild desert plants. Desert plants survive in harsh conditions with low water and nutrient content, which may partially be due to their endophytes. Research on desert plant endophytes has shown that, when applied to non-native hosts, they are able to increase nitrogen and phosphorus uptake and improve plant response to biotic and abiotic stressors. We have isolated several strains of endophytic Pseudomonas spp. from wild Agave palmeri in the Sonoran Desert and tested their ability to act as biofertilizers and biocontrol agents.When applied to crops such as Kentucky bluegrass, red clover, carrot, and coriander, Pseudomonas spp. strains were able to significantly improve root and shoot lengths. Additionally, when applied to drought-sensitive wheat, they were able to alleviate drought stress. Their growth promoting-abilities may be partially due to their participation in the rhizophagy cycle, a mechanism by which microbes cycle between a free-living soil phase and an endophytic phase, bringing in nutrients from the soil which are then extracted from the microbes via reactive oxygen-mediated degradation within root cells. Using confocal microscopy, we were able to show that Pseudomonas spp. become endophytic inside non-native hosts and participate in the rhizophagy cycle. Pseudomonas spp. were also able to inhibit the growth of phytopathogenic and non-phytopathogenic fungi. They do this by colonizing fungal hyphae, producing antifungal secondary metabolites, and producing antifungal volatile organic compounds (VOCs). However, despite the research into endophytes as biofertilizers and biocontrol agents, it is rare for those microbes to become commercial products. As such, we tested a commercially available biocontrol bacterium for its ability to improve plant growth in addition to its ability to control pathogens. Bacillus amyloliquefaciens Strain X from Company A improves plant growth when applied as a seed treatment or as a soil drench. Strain X becomes endophytic in a multitude of annual and perennial plants and participates in the rhizophagy cycle to improve host growth. Its entry into the plant can be improved by the addition of humic substances into the substrate. Out of the two commercially available products made with Strain X, the biopesticides Product Y and Product Z, only Product Z was able to improve tomato seed germination and seedling growth. Product Z should be considered for use as a biostimulant, potentially with the addition of humic acid.