Pinto bean seedlings 'UI 114' (Phaseolus vulgaris L.) were subjected to
temperatures between – 2° and – 5°C for periods ranging from 0.5 to 12 hr. The plants
that were not sprayed with a suspension of the nucleating Pseudomonas syringae bacteria
and those that were water-stressed to near wilting were most resistant to ice
nucleation. Plants with dry leaf surfaces were much more apt to supercool than those
with distilled water droplets on their leaves, whether inoculated with the bacteria or
not. Spraying the freeze-dried bacteria suspended in distilled water on the leaves increased
wettability and dew formation on the leaf surfaces. Tests with an oxytetracycline
preparation, which also increased wetting, suggested that a hydrophobic leaf
surface helps delay ice formation. Use of wetting agents in leaf sprays may be counterproductive
so far as supercooling stability is concerned. It is obvious that leaf water
relations interact with bacterial ice nucleation
