Plant breeders are making progress improving productivity of native grasses as well as agricultural crops. However, potential benefits of belowground traits such as mycorrhizal symbioses are not well explored. Our research addresses this knowledge gap by assessing mycorrhizal interactions with switchgrass (Panicum virgatum) ecotypes and sorghum (Sorghum bicolor) genotypes in complementary field and greenhouse studies. High nutrient and water-use efficiency associated with effective mycorrhizal symbioses are important for sustainable and economical agroecosystem production, as enhanced mycorrhizal associations can facilitate development of superior genotypes for high productivity in marginal soils. By understanding genetic mechanisms driving mycorrhizal symbioses, we can better inform breeders and land managers to simultaneously maximize biomass production, ecosystem services, and rebuild soil quality. We present information on relative mycorrhizal responsiveness [rMR = (DMmyco – DMnonmyco) / DMnonmyco), where DM is total dry mass] of 13 switchgrass ecotypes and 50 sorghum genotypes representing an expansive genetic gradient. Plants were grown in low-nutrient native prairie soil. Soils were either steam-pasteurized (non-mycorrhizal), or non-steamed (mycorrhizal). At harvest, roots were subsampled to quantify mycorrhizal fungal colonization. Dry mass of roots and shoots were combined for calculation of rMR. Additionally, we evaluated plant gene-expression and identified mycorrhizal fungal taxa associated with sorghum.
Results/Conclusions
Discovering genetic and ecological mechanisms related to functional AM symbioses expands the toolkits of plant breeders and land managers. We found evidence of a strong genetic component for rMR in switchgrass and sorghum, including evidence of differential plant gene-expression and associated AM fungal taxa across sorghum genotypes. Within switchgrass ecotypes, rMR is directly related to upland versus lowland populations, with upland populations expressing significantly greater rMR than lowland populations. We also found rMR patterns at a continental scale, with greatest rMR in switchgrass populations of the Central Great Plains. Principal Coordinate Analysis suggests lowland populations can be further separated into coastal and interior populations based on rMR. For sorghum, landrace (open-pollinated) genotypes were typically colonized by 3x more mycorrhizal fungal structures, presumably driving significantly and substantially greater rMR and biomass production, compared to commercial (fertilizer responsive) genotypes. Evidence suggests plant breeding can either increase or decrease rMR, depending on selective pressures, such as fertilizer rates. These findings indicate breeders can include sustainability traits, such as mycorrhizal responsiveness, as they develop improved germplasm. Ultimately, the concept of ‘mycorrhiza smart’ breeding can help us optimize agroecosystem production, decrease fertilizer requirements and downstream pollution, and regenerate global soil resources.