Genetic Variation of Hypocotyl Length in the Brussels Sprout

A study was made of variation in the hypocotyl length of two inbred lines of Brassica oleracea gemmifera (Brussels sprout). The pattern of means and variances obtained from parental, F1, F2 and backcross generations suggested polygenic control of hypocotyl length. Measurements of parental seed weights, embryo cell numbers, and the growth of seedlings from seeds of known weight support the view that variation between the lines in hypocotyl length, when the seedlings were exposed to light, was determined by differential extension rather than by initial differences in seed weight. The effect of reduction in light intensity on hypocotyl extension was studied and the differences between the lines was maintained under all light intensities. Differential reaction of the lines was only observed when the period allowed for growth was short. The inbred line with the longer hypocotyl was shown to suppress the other under competitive conditions.