User:David Johnston Monje/EndophyteNutrientAbstract

Plant and endophyte relationships: nutrient management

David Johnston-Monje and Manish N. Raizada$ Department of Plant Agriculture, University of Guelph, Guelph, ON Canada N1G 2W1

$Author for correspondence FAX: 1-519-763-8933 Phone: 1-519-824-4120 x53396 Email: raizada@uoguelph.ca

Keywords: Endophyte, biofertilizer, arbuscular mycorrhiza, rhizobia, Neotyphodium, growth promotion, biological nitrogen fixation, phosphate solubilization, ACC deaminase, nutrient uptake, root

Abstract

Endophytes are fungi and bacteria that live inside plants without causing disease. Endophytic associations date back to the first land plants and have contributed to their survival and evolution. An endophytic strain can infect multiple host genera yet exhibits genotype specificity within a species. Most endophytes originate from environmental infection, although a number can be transmitted via seed or vegetative propagation. Here we review how endophytes contribute to plant nutrient use efficiency (NUE) and their current and potential applications to agriculture. Endophytes can improve plant NUE by several mechanisms including formation of extra-root hyphae for nutrient absorption; stimulating root growth; altering plant metabolism to promote nitrogen and phosphate uptake; nitrogen fixation; and modifying soil directly or altering root exudates. Although many endophytic strains have been discovered, commercial endophytic inoculants for agriculture are limited to arbuscular mycorrhizae, rhizobia and Azospirillium; beneficial Clavicipitaceous fungi are also sold in the form of infected grass seed. Wider adoption of endophyte inoculants has been prevented by cheap synthetic fertilizers, variable responses by the endophyte depending on host genotype and environment, competition from endogenous microbes, host genotype specificity, poor establishment and persistence. Endophytes do have significant potential to improve agriculture, but this will require further discovery of novel endophytes, genetic improvement of both endophytes and their hosts, standardized testing and formulation. Novel genes and metabolites from endophytes represent an additional largely untapped resource for future agricultural biotechnology.