Root cortical aerenchyma in maize hybrids in Pennsylvania and interaction with mycorrhiza and soil-borne pathogens

Root cortical aerenchyma in maize hybrids in Pennsylvania and interaction with mycorrhiza and soil-borne pathogens

Summary

Arbuscular mycorrhizal colonization (AMC), and root pathogen infection (PI) in relation to root cortical aerenchyma (RCA) of hybrids commercially planted in Pennsylvania, are studied in this project. We have completed the activities proposed for the first semester, namely 1. Selection of sampling sites, 2. Greenhouse study planning; 3. Root pathogen assessment training; and 4. Data analysis of preliminary results. As a result of the first field harvest conducted in Summer 2013, we have found AMC values between 4 to 30 % in the corn hybrids planted in central Pennsylvania. We continue to measure RCA and PI on images already acquired during 2013 along the first part of Spring/2014. The contribution of this project to sustainable agriculture is focused in better understanding anatomical traits in root systems of corn that confer better resistance to drought and decreased nutrient availability.

Objectives/Performance Targets

The overall objective of this project is to evaluate the interaction of the anatomical trait root cortical aerenchyma (RCA) of corn hybrids with soil microorganisms in Central Pennsylvania.  The soil microbes we are studying in this project are arbuscular mycorrhizae forming fungi, and root pathogens. The former is detected by measuring arbuscular mycorrhizal colonization (AMC), and the latter can be quantified as pathogen infection (PI). AMC and PI will be used herein to mention the two soil-borne microbe groups in reference to their interaction with roots.

In general, we have successfully completed the activities planned for the first semester of the project. These activities are 1. Selection of sampling sites, 2. Greenhouse study planning; 3. Root pathogen assessment training; 4. Data analysis of preliminary results.

More specifically, we conducted the first field harvest on 30 commercial hybrids from one of the trials of the “Commercial Grain and Silage Hybrid Corn Tests” at the Russell E. Larson Agricultural Research Farm in Center Pennsylvania.  The results obtained from this harvest will serve as preliminary information about the variation of anatomical traits (RCA included), AMC and PI on commercial hybrids in the central zone of Pennsylvania.  We are currently performing laboratory analysis of root anatomy and AMC. Also, we have defined methods and techniques for addressing the specific objectives that include greenhouse studies in May 2014.  Future evaluations of root-infecting fungi in the greenhouse have required additional planning efforts in order to avoid contamination of the area with potential pathogens for other studies at the same facility. After several meetings with faculty members of the plant pathology department at Penn State University, we have initiated collaboration with Dr. Gretchen Kuldau, who will be advising on the experiments with root pathogens in greenhouse systems. The activities per objective executed this year are listed below:

• • Root crown samples collected from 32 experimental plots of the 2013 Grain and Silage Hybrid Corn Test at the Russell E. Larson Agricultural Research Farm research farm.  Two plants per plot were shoveled and washed, photographed and preserved for further analysis.

• • Images for digital shovelomics acquired and ready to be analyzed with the software ImageJ. These images will be used for measuring architectural traits on root crowns, like angles and lateral branching. These traits could be used as covariates or explanatory variables for better modeling the interaction of anatomical traits with AMC and RP.

• • Root segments taken in the collected samples were obtained according to described methods (Burton et al., 2013). The segments were then laser-ablated and images of the cross-root sections were acquired and edited for the subsequent analysis with RootScan. This is the software in use for obtaining anatomical traits like RCA developed by Burton et al. (2012).

• • Representative root subsamples from the plants described above were prepared for AMC assessment with the gridline-intersect method. The samples were cleared and stained according to Vierheilig et al. (1998) before the measurements could be performed.  Measurements are now completed.

• • Data analysis in progress.

• • Protocol, methods and supplies for preliminary trials prepared to be conducted in January 2014. 

Accomplishments/Milestones

August 2013
• Organized meetings with collaborator Dr. Gregory Roth, extension specialist at Penn State, to coordinate contributions to the project.
• Conducted first sampling event at the Russell E. Larson Agricultural Research Farm.
• Acquired images for digital shovelomics from field samples.
• Collected and prepared root samples for anatomical traits measurements, AMC, and PI assessment in the field.

September 2013
• Completed paperwork and facilitated administrative procedures in order to initiate project activities.
• Performed laser ablation of root segments in the field. 200 images are ready to be edited and analyzed with RootScan.
• Reviewed literature on available techniques for pathogen assessment in corn.

October 2013
• Held meetings with collaborator Dr. Gretchen Kuldau, professor of plant pathology, with the purpose of coordinate contributions to the project.
• Talked with Sara May, manager of the plant clinic at the Penn State University, to learn about current methods for assessing pathogen infection in field samples.
• Edited images for anatomical trait assessment with RootScan.

November 2013
• Coordinated activities for sampling and greenhouse experiments with staff members of our facilities (greenhouses, laboratories and farm).
• Prepared protocol for greenhouse preliminary trials in winter 2013.

December 2013
• Prepared supplies and needs for starting preliminary trials at the greenhouse in January 2014.
• Measured AMC.
• Prepared annual report.

Impacts and Contributions/Outcomes

The results obtained through this project will contribute to the development of sustainable agriculture by providing better understanding of root traits that could be used for selecting corn varieties with greater stress tolerance and reduced input requirements. 

Specifically this year, we have advanced in the description of AMC in 32 hybrids commercially planted in Pennsylvania.  AMC average values ranged 4 – 32 % of root length colonized. The samples consisted of the oldest root whorls (2^nd – 4^th) which present a consolidated anatomy, according to previous results (Burton et al., 2013). The general mean of AMC was 18%, with 80% of the hybrids in the range of 10 – 20%.  Previous results had shown that while both, main and lateral roots show similar trends in terms of AMC relative differences, do lateral roots exhibit the highest percent values. For this reason, we used the lateral roots for determining AMC. 

An important result this year was the possibility to study AMC with the laser ablation technique. We have been able to observe internal fungal structures in roots with this technique. We are still working on setting the parameters that will be used to create reliable procedures for the quantification of root fungal colonization simultaneously with anatomical traits. Being able to observe and quantify fungal colonization with the laser will open a new frontier in the field of root ecophysiology. 

• • Burton, A., Lynch, J., Brown, K., 2013. Spatial distribution and phenotypic variation in root cortical aerenchyma of corn (Zea mays L.). Plant and Soil 367, 263–274.

• • Burton, A., Williams, M., Lynch, J., Brown, K., 2012. RootScan: Software for high-throughput analysis of root anatomical traits. Plant and Soil 357, 189-203.

• • Verheilig, H., Coughlan, A.P., Wyss, U., Piche, Y., 1998. Ink and vinegar, a simple staining technique for arbuscular-mycorrhizal fungi. Appl Environ Microb 64, 5004-5007.

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