Basil vs Marigold for Tomato Spore Counts

ISEF Category: Plant Sciences

Subcategory: Pathology  ·  Difficulty: Intermediate  ·  Setup: School Lab  ·  Time: 1 to 2 Months

The Hook

Plant spacing can change more than yield. It can change what floats through the air. In a tomato patch, that means the mix of spores around the leaves may shift when you add basil or marigold. You can measure that with simple sticky traps and a Foldscope.

What Is It?

This project asks whether companion plants change the number of airborne spores near tomato plants. Airborne spores are tiny reproductive cells from fungi and similar organisms. Think of them like dust with a purpose. They drift on air currents, land on surfaces, and can start infections if conditions are right.

You would place Vaseline-coated index cards near tomato plants, then inspect the trapped particles under a Foldscope. A Foldscope is a paper microscope you can carry in a pocket. You would compare cards from tomato-only plots with cards from plots that include basil or marigold. The main idea is simple, count what lands on the traps, then see whether one planting pattern shifts the spore load.

This is not about proving that basil or marigold cures plant disease. It is about testing whether plant neighbors change the local microenvironment. That can happen through airflow, humidity, leaf structure, or volatile compounds from the plants themselves.

Why This Is a Good Topic

This is a strong science fair topic because you can test a clear question with visible data. You do not need a university lab to collect samples and count particles, but you still get to work with real biological evidence. The project connects to crop health, disease spread, and low-cost field monitoring. You can learn sampling design, microscopy, control plots, and basic statistics without needing advanced equipment.

Research Questions

• How does intercropping basil change airborne spore counts near tomato plants compared with tomatoes grown alone?
• How does intercropping marigold change airborne spore counts near tomato plants compared with tomatoes grown alone?
• What is the effect of plant spacing on airborne spore counts in a tomato patch with basil or marigold?
• To what extent do different trap heights change the number of spores collected near intercropped tomatoes?
• Which companion plant, basil or marigold, is associated with lower spore counts on sticky cards near tomatoes?
• Does the time of day affect airborne spore counts in tomato plots with and without companion plants?

Basic Materials

• Tomato plants grown in comparable plots or containers.
• Basil plants and marigold plants.
• Index cards or microscope slides.
• Petroleum jelly or Vaseline.
• Foldscope or other simple microscope.
• Fine-tip permanent marker.
• Ruler or measuring tape.
• Digital camera or smartphone with camera.
• Gloves for handling sticky traps.
• Data sheet or notebook.
• Graph paper or spreadsheet software.

Advanced Materials

• Portable air sampler for comparison studies.
• Compound microscope with camera adapter.
• Hemocytometer or calibrated counting chamber.
• Spore stain or mounting medium for clearer imaging.
• Environmental sensor for humidity, temperature, and wind.
• GPS-tagged field notebook or mapping app.
• Image analysis software such as ImageJ.
• Statistical software such as R or Python.
• Sterile forceps and labeled storage boxes for trap handling.

Software & Tools

• ImageJ: Measures particle size, counts trapped spores, and helps you compare images across plots.
• Google Sheets: Organizes counts, builds graphs, and tracks sampling conditions.
• R: Tests whether differences between plant treatments are statistically meaningful.
• Python: Automates image cleanup, counting, and summary plots if you want a coding angle.
• Foldscope app: Helps you document microscope images and keep trap photos organized.

Experiment Steps

1. Define the plot design and decide how many tomato-only, basil, and marigold sites you can compare fairly.
2. Choose one sampling setup for all sites so trap height, trap location, and trap exposure stay consistent.
3. Plan how you will identify and count particles under the microscope before you collect field data.
4. Build a control plan that separates plant effects from weather, shading, and nearby sources of dust or fungal material.
5. Decide how you will turn raw counts into a fair comparison, such as counts per card area or per inspection field.
6. Preplan your statistics so you can compare treatments and report uncertainty clearly.

Common Pitfalls

• Placing traps at different heights, which changes how many spores each card can catch.
• Comparing plots with different sun, shade, or airflow, which makes plant effects hard to separate from site effects.
• Letting the Vaseline layer vary from card to card, which changes how well particles stick.
• Counting every speck as a spore, which inflates results because dust and debris can look similar under a simple microscope.
• Sampling only once, which misses day-to-day variation in spore load.

What Makes This Competitive

A stronger project goes beyond a simple before-and-after comparison. You can improve it by using matched control plots, repeated sampling, and image-based counting with clear rules. You can also test whether one companion plant changes not just total particles, but the size or shape profile of trapped material. If you connect your field counts to weather data or plant spacing, your results will feel more like real ecological research.

Project Variations

• Use basil, marigold, and cilantro side by side to compare whether different aromatic companions shift spore counts differently.
• Replace tomato beds with potted tomatoes indoors to test whether the effect still appears in a more controlled setting.
• Pair sticky-card counts with leaf disease scoring to see whether lower airborne spore counts line up with fewer visible symptoms.

Learn More

• USDA Plant Disease resources: Search the USDA and APHIS sites for guides on fungal plant pathogens and disease scouting.
• NIH PubMed: Search review articles on airborne fungal spores, plant disease spread, and passive spore trapping.
• NOAA Climate.gov: Use weather background pages to understand how humidity, wind, and rain affect airborne particles.
• Plant Pathology journal: Search recent review articles and field studies on spore dispersal and disease monitoring.
• MIT OpenCourseWare: Search biology and ecology course materials for sampling design, controls, and basic statistics.