Phylogenetic Disease Ecology of Plants

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

This research explores three predictions that follow from a simple idea: that pathogens can often attack multiple species, and two host species are more likely to share a pathogen when they are closely related to each other. The first prediction is that by taking the relationships among different pathogen species and different hosts species that they infect into account, we will improve our ability to predict which plants can be affected by which pathogens in nature. This prediction will be tested with a variety of plants and their pathogens. The second prediction is that when a new plant species (such as a crop) is introduced into an area, pathogens that infect close relatives already growing there will be most likely to 'spill over' and affect the new crop. The last prediction is that because pathogens are less likely to spread between species that are not closely related, mixtures of crop species could be designed to reduce problems due to diseases in agriculture. In the process of testing these predictions, the researchers will develop new analytical tools for the study of plant disease. This work will aid in developing new strategies for protecting crop plants from disease, and for protecting other valuable plant resources. The large training component of this project will include high school classes, college classes, senior thesis students, and PhD students. These students will learn skills from many fields that have both basic science and economic importance, including forest ecology, ecological monitoring, ecology of agricultural systems, ecological horticulture and bioinformatics. This project will test predictions regarding the relationship between phylogenetic relatedness of hosts and the host ranges of the pathogens that infect them. For each of the three components of the project, the researchers will take advantage of a previously developed and validated quantitative model that predicts how pathogen host ranges are constrained by the evolutionary relationships among host plants. In a novel application of network theory, the researchers will incorporate phylogenetic structure into network models for plant-pathogen interactions. They will use a metagenomics approach (identifying all fungal species growing inside plants by extracting and sequencing their DNA) to characterize the plant-pathogen networks of three plant communities, and will test predictions against the empirical networks. Novel hosts will be used in a transplant experiment in the field and an inoculation experiment in the laboratory to measure which local fungi colonize novel hosts, and how the phylogenetic structure of local plant-fungus networks affects fungal spillover to novel hosts. Finally, collaborating with a certified organic research farm, the PIs will test whether phylogenetically diverse cover crops have reduced disease pressure, a hypothesis called the "Dilution Effect", and whether greater phylogenetic distance among intercropped species suppresses disease.