Evaluation of chicory seeds maturity by chlorophyll fluorescence imaging

Chicory (Cichorium intybus L.) seed production includes sorting to remove foreign materials
and non-viable seeds. A machine vision system was developed to monitor the fluorescence
in order to detect the immature chicory seeds. It comprised a monochromatic light source,
a highpass filter and a monochromatic CCD camera sensitive to red and infrared. With this
device, blue light reflected by the seeds was blocked whilst red fluorescence was measured
by the camera. A segmentation algorithm was designed to estimate separately the fluorescence
intensities of the pappus, a crown of scales, and the main body of the pericarp.
Experiments were carried out on five clones of cross-pollinated chicory plants used for
seed production. Two hundred flower heads were labelled at flowering and harvested at
different times during the maturation process expressed in “days after flowering” (DAF).
Germination tests were performed according to the recommendations of the International
Seed Testing Association to measure the germination percentage (GP) and the germination
rate (GR), an indicator of seed vigour. Seed chlorophyll content diminished during maturation
following a different logistic trend for the pappus and the pericarp. The GP increased
from 18 DAF to reach its maximum value at 21 DAF, but the GR remained low until 30 DAF
and increased afterwards. The potential of chlorophyll fluorescence to be used as an
indicator of chicory seed vigour was the greatest between 21 and 36 DAF.