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ARS Home » Southeast Area » Raleigh, North Carolina » Plant Science Research » Research » Research Project #441930

Research Project: The Effect of the Defense Response and the Microbiome on Heterosis in Maize

Location: Plant Science Research

Project Number: 6070-21220-016-018-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Jun 1, 2022
End Date: May 31, 2027

Many crops grown on commercial farms are hybrid cultivars because these hybrid plants are reliably healthier, larger, and more productive than their inbred parent lines. The widespread and valuable phenomenon of hybrid superiority is called heterosis. Corn (or maize) displays an extremely high level of heterosis. Despite over a century of intensive research into heterosis, it is unclear how or why hybrid genomes give rise to superior phenotypes. Most hypotheses and research thus far have focused on genetic and physiological mechanisms of heterosis. It has become increasingly clear over the last decade that the microbes within and around plants (the microbiome) profoundly affect most aspects of the plant’s growth. With our collaborators, we have recently shown that the microbiome affects the extent to which heterosis is observed in maize, although this effect is variable depending on the environment. This agreement is being set up to fund a collaboration with North Carolina State University to further our understanding of how heterosis effects, and is affected by, pathogenic and non-pathogenic microbes in the environment. In particular, we are interested in comparing how inbred and hybrid plants respond to pathogenic and non-pathogenic organisms. We have two hypotheses: 1. Hybrids are more resistant to minor (facultative) pathogens in the environment than inbred lines. 2. Hybrid varieties do not ‘waste’ as many resources mounting inefficient defense responses as inbred lines do. There is evidence in the literature to support both these hypotheses, but these questions have never been directly addressed in maize. It is possible that both hypotheses are true.

We will be assessing the response of different maize lines and hybrids to the presence of pathogenic and non-pathogenic microbes and we will be addressing the following questions: 1. Do hybrid maize varieties respond to microbes (both pathogenic and non-pathogenic) in the same way and with the same intensity as inbred lines? 2. Do the same genes affect disease resistance and defense response in inbred lines and hybrid varieties? We have developed more than 500 crosses and inbred lines to test for variation in disease resistance, defense response and various growth phenotypes when measured in natural and microbe-manipulated environments. To address question #1, we will be growing these lines in growth chambers and will inoculate them with various pathogens or expose them to various microbe-associated proteins that we have shown to elicit a defense response in maize. We will measure the defense response using a variety of physiological and molecular assays, measuring traits such as gene expression and the production of reactive oxygen species. We are also growing these hybrids, together with their inbred parents, in three replicated field trials that will each be inoculated with three different maize foliar diseases. We will rate these trials over the summer of 2022 and will repeat the experiment over the next two summers. Using these data, we will be able to address question #2.