THE GENETIC BASIS OF MAIZE RESPONSE TO ARBUSCULAR MYCORRHIZAL FUNGI

OVERVIEWSince first colonizing land, plants have relied on beneficial associations with microorganisms to gain access to soil nutrients. Today's major crop species retain this capacity to form symbioses with soil microbes, although these interactions may not be optimized for agricultural systems. The agroecosystem exposes these ancient associations to a high-input environment that differs greatly from that in which they evolved. Furthermore, modern crop varieties are the product of intensive artificial selection under these same high-input conditions. To fully realize the potential of microbial interactions in agriculture, we require a better understanding of when, why and how they will have the greatest benefit. In this project, we will characterize the drivers of variation in maize (Zea mays; corn) response to arbuscular mycorrhizal (AM) fungi. Specifically, we will 1) identify variety-specific host molecular and physiological responses to inoculation with diverse AM fungi and 2) map the genetic architecture of AM host response in the context of the abiotic and biotic environment of the cultivated field. We will compare maize lines previously identified to differ in AM host response using a combination of fine-scale analysis in controlled conditions and genetic mapping in the field. For field experiments, we will use a design we have developed to selectively incorporate plant AM-incompatibility genes into our mapping populations to estimate AM effects.INTELLECTUAL MERITThe balance of cost and benefit in symbioses is dynamic, and there is a fine line between mutualism and parasitism. The prevailing hypothesis states that agricultural intensification has reduced the benefit crop plants can derive from microbial interactions. Although fundamental to the application of plant-microbial associations, this hypothesis has been difficult to address. Manipulation of microbial communities in the field at the scale required for meaningful evaluation of yield components is logistically challenging. This project will use a novel mapping strategy to estimate the impact of a major crop-microbial mutualism under cultivation. In conjunction with molecular and physiological characterization, including profiling of the AM fungal and broader microbial communities, our experiments will distinguish dependence on symbiosis from benefit - concepts that have previously been difficult to pin down. We will assess trade-offs between the performance of symbiotic and non-symbiotic plants with implication as to the extent to which breeding for high-input agriculture can also be aligned with maintaining the capacity of plants to benefit fully from AM associations.BROADER IMPACTSAs society demands more sustainable agriculture, it is important to develop robust methodologies to evaluate the viability and potential benefits of alternatives to conventional practice. This work will contribute substantially to our understanding of the role of crop-microbial mutualisms and the degree to which the breeding process needs to take account of these interactions if we are to benefit fully from them. The inherent appeal of the integration of beneficial microbes into farming systems presents an excellent opportunity to engage the broader community in learning about biotic interactions, plant genetics, and the future of sustainable agriculture. We will use AM fungi incompatible maize varieties to provide a striking visual demonstration of the importance of symbiotic soil microbes to crop performance. We will collaborate with existing PSU extension and outreach partners to communicate findings from this project to the agronomic research, farming, and broader community. We will participate in an existing range of activities, presenting annually in PSU's principal agricultural outreach show and a local agricultural fair. We will develop and host an annual tour of our research field and facilities for Middle School students. We will engage with the Penn State Arboretum to develop a living exhibit of AM compatible and incompatible varieties growing side-by-side and available for the public. We will build on project team experience and existing collaborations to produce on-line and printed content explaining the importance of beneficial plant-microbe interactions to young audiences