Articles
INFRARED PHOTOGRAPHY AND VIDEO TECHNIQUE FOR VISUALIZATION OF FIRE BLIGHT INTERNAL LESIONS
Such lesions, on trunks and limbs may be very difficult to detect, especially if they originate from late infections (September-October).
We have checked that a technique previously described by SPECHT and BEER (1975) gives satisfactory results to visualize otherwise undetectable lesions, provided suitable filters and films are used.
Histological studies of tissues of the surface of lesions and their surroundings show modifications in the shape of cells of the cortical parenchyma invaded by the bacteria.
There is no clear-cut limit between healthy and diseased tissues, but a progressive evolution.
The study of the optical properties of these tissues with a spectrophotometer shows that the IR radiations are much more absorbed when histological modifications of cortical parenchyma are more important.
The strongest difference is observed for radiations comprised between 700 and 900 nm which correspond to the sensitivity of IR films.
These facts explain the good quality of the contrast shown by pictures obtained with IR photography associated with a filter or with a video-system equiped with the same filter.
Obviously such a video system would be much more convenient for practical use in the orchard.