A COMPARATIVE INVESTIGATION OF SEED-GERMINATION, METABOLISM AND SEEDLING GROWTH BETWEEN 2 POLYPLOID TRITICUM SPECIES

The embryo and seedling growth patterns of two Triticum polyploid spec ies, namely the tetraploid, T. durum (AABB), and the hexaploid, T. aes tivum (AABBDD), were compared. Two developmental phases were identifie d, an initial lag phase during embryo growth and an exponential phase during seedling growth. These developmental phases were distinctly dif ferent in the two species. The initiation of mitosis prior to the ince ption of the exponential phase, occurred at 16 hours after imbibition in the hexaploid and 20 hours after imbibition in the tetraploid. All the growth rates of the hexaploid, except that of the shoot, showed hi gher activities-food reserves were mobilized much faster, root growth was faster, number of cells in mitosis over 24 hours higher: for the h exaploid primary root (7.0%) and first pair of lateral roots (6.5%), w hile for the tetraploid it was found to be 5.9% in the primary root an d 5.7% in the first pair of lateral roots. The primary root and first pair of lateral roots of the hexaploid emerged respectively six hours and four hours earlier in comparison to those of the tetraploid. The i nception time of the exponential phase in seedling growth and mobiliza tion of food reserves were observed 12 hours earlier in the hexaploid although no differences were observed in the inception times for the s hoot growth and respiration rate. It can therefore be concluded that t he genomic composition of the hexaploid promotes a higher growth rate and therefore a higher metabolic rate than the tetraploid.