| Results and Discussion The (Ae. sharonensis x T. monococcum) amphidiploid exhibited similar developmental responses (days to floral initiation, final leaf number and days to anthesis) under both long and short photoperiod as T. monococcum, except spikelet number where it was signiflcantly (p<.01) lower than T. monococcum under short photoperiod (Table 1). Ae. sharonensis possessed a strong vernalization response while T. monococcum possessed little or no response as indicated by its final leaf number (when vernalized and under long photo-period) being close to the minimum for wheat. The (Ae. sharonensis x T. monococcum) amphidiploid was very similar to T. monococcum in vernalization response, indicating epi-stasis of T. monococcum over Ae. sharonensis genes for this character. The close similarity in developmental responses between the (Ae. sharnonensis x T. turgidum dicoccoides : cereal type) amphidiploid and those of T. turgidum dicoccoides is evidence for epistasis (A genome) or dominance (B genome) of genes for vernalization response in the amphidiploid over those in Ae. sharonensis. The similar developmental responses of the (Ae. sharonensis x T. monococcum) amphidiploid with those of T. monococcum is compatible with the notion of the first tetraploid wheats occupying similar habitats as T. monococcum, but eventually replacing it through superior competitive ability. The most significant changes in yield potential of the Ae. sharonensis x T. monococcum amphidiploid over T. monococcum were a substantial increase in both Kernel weight and grain number per spikelet (Table 2). Spikelet number per head was significantly (p < .01) decreased compared with T. monococcum but significantly (p < .01) higher than Ae. sharonensis. A previous report (SEARS 1941) has been made of increased grain size of synthetic tetraploid wheat over its diploid parents. This could have arisen as a consequence of favourable interaction between genes influencing grain size in the two parents and/or as a consequence of tetraploidy, more likely due mostly to the former. Previous studies of the genetic control of kernel weight in hexaploid wheat (HALLORAN 1976) revealed genes of major effect on its expression in both the A and B genomes. This observation is compatible with the knowledge that kernel weight appears to reach a maximum in tetraploid wheat with decreased weight accompanying the evolution of hexaploid wheat (HALLORAN & PENNELL 1981). The fertility of the (Ae. sharonensis x T. monococcum) amphidiploid was similar to T. monococcum. This, together with the increase in kernel weight of the amphidiploid over the diploid parents indicates high combining ability between the A and B genomes. A previous report has been made of the comparatively high combining ability of the A and B genomes, as seen in advanced tetraploids of wheat, against the low level exhibited by the A and D genomes, in the T. monococcum x Ae. squarrosa hybrid (SHEBESKI 1958). |
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