Wilt Disease Ratings

Tomato plants

This protocol is more of a series of guidelines than steps in a particular order.

• Measure symptoms as long as is necessary. Generally daily measurements for 1-14 days for susceptible tomato grown at 28C. If you do a cool temperature assay or a more resistant plant, you might want to rate longer. Basically… rate long enough to get the full disease progression (where it plateaus)
• Measure symptoms on individual plants daily using the 0-4 Disease scale:
  • 0: asymptomatic
  • 1: up to 25% leaflets wilted
  • 2: up to 50% leaflets wilted
  • 3: up to 75% leaflets wilted
  • 4: up to 100% leaflets wilted
• Wilted leaflets have a loss of turgor (i.e. they are floppy). They usually become somewhat darker green, but can become chlorotic (yellow) instead. The edges of the leaflets will curl upwards on wilted leaflet. This is a good indication that the leaflet is wilted, but assessing turgor with a finger tap is the best method.
  • This video shows a disease index 4 tomato plant: https://youtu.be/-0GrCAA3-Dw
• Until you have rated many, many plants, you should count the #s of wilted vs. total leaflets to get those percentages. However, always hunt for symptoms before counting the leaflets. If there are 0 or 100% wilted leaflets… you can just record 0 or 4. Don’t waste your time counting things that are unnecessary :)
• Mark each plant with a plant stake labeled A, B, C, …, O.
• Print a Disease Progress sheet to record the wilt symptoms on each plant. Feel free to use this: https://docs.google.com/spreadsheets/d/1_eTl6RCoMsNviT5RWQlet7EY1owxHaFsRs-hOPhOAnQ/edit?usp=sharing
• For best results, aim to rate the plants at a consistent time each day (e.g. afternoon or morning).
• Don’t mistake thirsty plant wilt for bacterial wilt. If the plant is large relative to the soil, and the soil is very dry … the wilt might be due to dry soil. Plants generally recover from water-stress wilt after 1 hour. Your healthy control plants will be your friend here.
• Symptoms won’t appear on days 1-2, but you must keep the plants watered, especially if it’s a soil soak. Ralstonia die off in dry soil. For petiole inoculations, the symptom appearance is fairly synchronized. Soil-soak inoculations are more stochastic.
• day 0 is inoculation day

Don’t forget to analyze the data! There is an excel template in the shared Box folder in the 1 – be organized folder.