The findings were revealed by James Hutton Institute researcher Dr Danny Cullen has at the Fruit for the Future event (18 July).
Demonstrating how the £6,000 IRT camera can be used in the field, he said: "By using IRT you can measure these traits quickly and non-destructively, speeding up the breeding process.
"Closure of the plant's stomata indicates water stress, which shows up as warmer. But higher temperatures in the leaf canopy can also provide early detection of pest and disease pressure, from vine weevil or root rot.
"There's work to be done to determine how susceptibility relates to water stress. We aim to validate this method for soft fruit - that's what I'm interested in. But this could be applied to any crop."