Question 3
Which of these is usually worth more to a farmer than a higher yield?
The right answer is the one marked above.
Resistance to a disease that destroys the crop. A high yield is worth nothing if the harvest is lost. Resistance protects the whole crop rather than improving part of it.
And the work never finishes: the organism causing the disease also changes, by mutation, so resistant varieties eventually stop working and have to be bred again.