Human population levels are anticipated to reach 11 billion by 2100. The United Nations predicts that food production must increase by 70% to feed this projected level of growth but changing weather conditions and limited natural resources such as water, arable land, and soil nutrients already constrain the expansion of global agriculture. To meet current demands, agriculture is highly dependent on chemical inputs such as N- and P-based fertilizers. However, this dependence on chemical inputs is not economically or environmentally sustainable as these industrial fertilizers negatively impact the environment through both their production and use. As such, plant-associated microorganisms can increase nutrient availability and plant growth while reducing reliance on petrochemicals. Endophytes isolated from organic Coffea arabica plants were screened for N-fixation, phosphate solubilization, siderophore production, and auxin production. These endophytes were shown to increase biomass and yield when cross-inoculated into agricultural species including tomato, peppers, rice, and corn. N-fixation by these endophytes was indirectly assessed via acetylene reduction assay. The future of sustainable agriculture greatly depends on the ability to enhance crop yield while protecting the future production potential of arable croplands. Further insight into the processes involved in plant-microbe interactions could mitigate negative impacts to global agriculture.
Results/Conclusions
A suite of endophyte species were cultured from surface-sterilized branch cuttings of organically grown Coffea arabica. We detected significant effects of endophyte inoculation on crop plants growth and yield when inoculated with a consortia C. arabica associated endophytes. 16s rDNA identification of these microbes indicate a variety of species including members of Novosphingobium, Burkholderia, Sphingomonas, Enterobacteria, Pseudomonas, Stenotrophomonas, Methylobacterium, and Rhizobi. Endophytes were initially cultivated on nitrogen limited combined carbon media and rescreened on nitrogen free media. Isolates were further screened on nitrogen-free phosphate plates to identify the ability to solubilize phosphate increasing bioavailability to plants. Furthermore, isolates were grown in TYC broth with and without Tryptophan to test for indole-3-acetic acid (IAA) production. Since phosphorous bioavailability is also a limiting factor for plant growth and development, strains were grown for 48 hours in –PO4 solutions, pH changes were tracked, isolates were replated on nutrient agar for 72 hours, and CFUs were determined. C. arabica diazatrophs were inoculated into the rhizosphere of tomato, pepper, rice and corn seedlings. Plants receiving a cross-host inoculation showed an increased above and below ground biomass, advanced phenology and yield, and overall better health when grown in low nitrogen conditions.