After measurements of the hypocotyl and the radicle were made for all seedlings, the results were combined to obtain a vigour index. The index for lettuce was defined as follows:
Vigour = wg x growth + wu x uniformity where the w's represented associated weights with the parameters being multiplied;
where the maximum value is 1000 and lh and lr are the sample means of the hypo-cotyl length and the radicle length and uniformity = max (1000 - (wh X sh + wr X sr + wtotal X stotal + wr/h X sr/h)
where numdead refers to the number of dead seeds, the minimum value is 0, and sh, sr, stotal and sr/h are the sample standard deviations of the hypocotyl length, radicle length, total length and the ratio of the hypocotyl and radicle lengths.
Before processing, soybean seedlings were classified into alphabetical types based on the characteristics of their skeletons. The six types recognized by the program were the I, T, Y, P, A and M seedling types and are also examples of differing seedling shapes (Hoffmaster, 2002; Hoffmaster et al., 2003).
Maize seedlings possess a differing root structure that is composed of multiple roots (i.e. seminal and primary roots) connected to each seed when compared to soybean seedlings. The multiple roots present connection problems to the seed because of shadows and create an overlap problem in determining which root belongs to which seed. To address these issues, a different approach was used for maize seedlings than for lettuce and soybean seedlings.
As a first step, maize seeds were identified based on their yellowish-red colour. To accomplish this, a synthesized image of maize seeds was used as a training image. In suv colour space, the range of s-, u- and v-value colours that maize seeds fall into was established. The red, green, blue (RGB) maize image was then transformed into suv colour space.
Roots were separated by their white colour against the brown background of the germination paper. When disconnected, roots were encountered and assigned to the seed that was nearest to it.
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