Glomeromycota associated with Mexican native maize landraces in Los Tuxtlas, Mexico

Abstract

Many native maize landraces are still cultivated by different ethnic groups in Mexico as part of traditional polyculture systems (milpas). However, these systems and landraces are being steadily replaced by fertilized monocultures of genetically improved varieties or maize hybrids. Little is known about how such changes may affect the belowground community of maize symbionts. A greenhouse experiment was conducted to assess the composition of the indigenous arbuscular mycorrhizal fungi (AMF) communities colonizing four Popoluca maize landraces and the hybrid Texcoco, and to determine how these communities are influenced by the level of phosphorus fertilization. Fragments of AMF ribosomal DNA (rDNA) were amplified using nested PCR, producing 327 Glomeromycota sequences. Phylogenetic analysis assigned the Glomeromycota sequences into 84 operational taxonomic units (OTUs). This number of OTUs more than doubles the figure previously reported for maize exposed to AMF native inoculum. Exclusive or very heterogeneous maize type-AMF associations were rare. Most AMF species colonized 2–4 maize types. This suggests that the high diversity of AMF in milpas is related to the presence of several native maize landraces and that replacement of these landraces with a single hybrid may diminish AMF community richness. All landraces associated with more OTUs under moderate P, compared to low P fertilization, suggesting that low inorganic phosphate (Pi) in milpas is limiting symbiotic interactions. However, only 0–20% of OTUs were conserved between different P conditions for each landrace. The Black landrace, which presented the highest AMF colonization and Pi uptake, was associated with the highest number of AMF OTUs, supporting previous suggestions regarding this functional relationship with AMF richness.