Two strong varieties can share the same weak spot
- The idea
- Predict
- See it
- Why
- Check
The idea
“Pair the two varieties that each resist the most, and the field is covered.”
More resistance sounds like more protection, so pairing the two strongest varieties feels safe. Their strengths can overlap, and so can their weak spots.
The short version
The mistake: Pair the two varieties that each resist the most, and the field is covered.
What's actually true: Two varieties cover each other only if, for every threat, at least one of them resists it.
- Each variety resists a set of strains. A pair covers a strain if at least one of the two varieties resists it.
- So check the gaps, not the totals. A strain that both varieties are susceptible to can spread through the whole planting.
- The best partner resists what the first variety can't, even if it resists little else.
- This is why genetic variation helps a population. When individuals resist different threats, one new threat is less likely to kill them all.
On the exam: Go threat by threat. If both fail on the same one, the pair fails.