Student Spotlight: Cullen Dixon

Aug. 8, 2023
Cullen collecting beetles at Waterman

Today we're highlighting Cullen Dixon, a Translational Plant Science PhD Candidate in Dr. Andrea Gschwend’s Grapevine Genetics Laboratory here in the department of Horticulture and Crop Science.

Cullen grew up in mountainous Frackville, Pennsylvania but would often take trips out to visit his mom's side of the family who farm in Kentucky. His initial interest in plant science stems from helping on the family farm and his enjoyment of science over the years which helped him realize that plant genetics would be a good fit for him. 

He received his Bachelor of Science in Plant Science (2019) from Penn State University before ultimately deciding to pursue graduate school at The Ohio State University "due to [our] prestigious ranking nationally in the field of plant genetics and the highly unique programmatic structure requiring very little coursework and a strong focus on research, mentorship, outreach, education through workshops and seminars, and the ability to undertake an internship in industry during my studies".

As a PhD candidate, Cullen's research "aims to elucidate the genetic factors underpinning an observed increased insect-herbivory resistance in grapevine native to the northern/northeastern U.S. and southern Canada (Vitis labrusca) compared to European grapevine (Vitis vinifera). This work is very multi-faceted, providing a broad overview of resistance, succeeded by studies of specific genes/gene families of interest. Insect-herbivory observational studies, in silico genome investigations, phylogenetics, transcriptomics, and metabolomics will be employed to capture a wholistic understanding of the insect-herbivory defense response between species. The ultimate goal of my work is to provide breeders and geneticists with target genes to introgress or engineer into existing crop plants to decrease insect predation and increase yields."

In addition to his research, class, and lab involvements, Cullen is also highly engaged with our department, regularly participating in departmental socials, seminars, and symposiums. Additionally, he was able to pursue an internship with Corteva Agriscience this past summer (2022). 

Cullen was gracious enough to let us glimpse further into what an afternoon as a PhD candidate is like. The day we captured revolved around his Japanese Beetle feeding study on grapevine which took place in the Howlett Greenhouse and Waterman Agricultural and Natural Resources Laboratory (Waterman).



Wow! 90 seconds goes by quick - here's a more detailed explanation of what you saw in the video:

Step 1: Beetle Collection

  • Experimental prep begins the day before by placing traps around Waterman to collect the Japanese Beetles.
  • Around 4-5pm he collects the Japanese Beetles traps set around Waterman. The traps are made of an emitter, plastic bag & a post to hang them both on. The emitter releases a pheromone to lure the beetles in (smells like a powerful flowery perfume) once the beetles land in the plastic bag the sides are too slick & narrow for them to get back out. 
  • The collected beetles are then brought back to the Howlett Greenhouse to spend the night in a "Bugdorm" with limited food before the experiment begins the next morning around 9-10am.

Step 2: Grapevine Leaf Selection

  • He selects a few grapevines from the Gschwend Lab greenhouse for the experiment and brings them into the headhouse.
  • Prep continues by gathering all necessary supplies + labels for the experiment. 
  • Selection of target leaves for feeding begins - care is taken to ensure leaves are consistent across the experiment (mature leaves of comparable size & placement on the plant).
  • Chosen leaf is photographed against a standardized photo board before feeding begins as a reference photo. The photo board helps accurately gage the surface area later (it contains a quarter for scale).
  • Select a ring stand + beetle container to hold the chosen leaf in place.
    • The ring stand was made with input from a wide variety of individuals within the lab, OSU extension, the greenhouse, and Corteva AgriScience; Its design was challenging but of particular importance and because his experiments require the beetles to only feed on specific sides of the leaf. It was further complicated as beetles generally only like to feed under specific conditions – high light, moderate humidity, low wind. 
    • Airholes were added to containers since both beetles and the plant need air movement.

Step 3: Beetle Introduced to Grapevine Leaf

  • Select a moving beetle from the Bugdorm “they’re more vigorous & likely more apt to feed”.
  • He “presents” the chosen beetle a specific side of the leaf to feed on (either top or bottom) but it’sultimately the beetle’s choice which side of the leaf they end up feeding on (or if they even choose to feed at all).
  • Wait for the beetle to begin feeding.

Step 4: Leaf Preservation in Liquid Nitrogen

  • 1 hour after the beetle began feeding on the leaf - it's time to collect them and release them back outside.
  • Cut the leaf that has been fed on & lay it as flat as possible on the photo board, take a picture, grab a labeled tube, put the leaf into tube, then place it all straight into the liquid nitrogen – all of this being done rapidly. 
  • This quick process freezes the state of the transcriptome (state of expression of all the genes) and the metabolome (state of all the metabolites in the plant) so that later he will be able to evaluate them. 
    • AKA - the liquid nitrogen preserves the response state of the leaves, later allowing us to see what the gene expression was and what metabolites were being formed in the leaf tissues upon the Japanese Beetles feeding. 

Step 5: Clean Up

  • The last step is cleaning everything up and marking the experimented plants with a flag indicating when it was last experimented with.
  • His lab will wait a minimum of 3-4 days before using the plant again since they don't want the plant to have any defensive responses to beetles feeding on it in the future.

Repeat experiment for as many replicants as necessary.

Cullen's projected graduation is May of 2024 - Learn more about the research going on in the Gschwend Lab and prospective graduate student opportunities.