|Abstract or Summary
- Effect of temperature on seed dormancy, alpha-amylase activity and kernel weight in five wheat (Triticum aestivum L.) varieties was studied. Three ripening temperature conditions - 15.5°C, 26.6 °C and "Field" were used to induce dormancy. Alpha-amylase activity and kernel weight of developing kernels was determined every ten days after anthesis until maturity. Dormancy in kernels was examined at germination temperatures of 15. 5°C, 20°C and 26. 6°C. Alpha- amylase activity during germination of kernels was determined on 1st, 2nd, 3rd and 6th day. In developing kernels alpha-amylase activity peaked at 10 to 20 days after anthesis and dropped or levelled-off as the kernels approached maturity. This was observed at both 15.5°C and 26.6° C . However, the peak was not obvious at 26.6°C because of the enzyme activity was lower at this temperature than at 15.5°C. In kernels ripened in field, the enzyme activity fluctuated apparently depending upon the changes in weather conditions, especially temperature. A faster growth of kernels and higher final dry kernel weight were noticed at 26.6°C and field temperature conditions than at 15.5°C. Significant varietal differences were observed in both alpha-amylase activity in kernels and kernel weight during the development and maturation of kernels. Kernels of all varieties, ripened at 26.6 °C, germinated as fast as non-dormant check kernels at 15.5°C but exhibited varying degrees of dormancy when germinated at 20 °C and 26.6°C. In contrast, kernels of Brevor, Tom Thumb and P.I. 178211, ripened at 15.5 °C showed a high level of dormancy as shown by their failure to germinate at 20 °C and 26.6 °C, and slow germination at 15.5⁰ C. Kernels of Hyslop and Yamhill, ripened at 15.5°C, did not show dormancy at 15.5°C but showed some dormancy at 20°C and 26.6°C. This dormancy, however, was less than in Brevor, Tom Thumb and P.I. 178211. Field ripened kernels of Yamhill and Hyslpp when germinated at 15.5°C, did not show any dormancy; whereas, P.I. 178211, Brevor and Tom Thumb expressed different degrees of dormancy. Kernels of all varieties, ripened in the field, when germinated at 20°C or 26.6 °C, showed different degrees of dormancy except Yamhill. Yamhill did not differ significantly from the one year old non-dormant check kernels at 26.6° C . A substantial increse in alpha-amylase occurred only in germinated kernels. Although kernels of all varieties ripened at 26.6°C showed about the same weighted germination percentage at 15.5°C, germinated kernels of Yamhill, Hyslop and P.I. 178211 and had highly significant greater alpha-amylase activity than those of Brevor and Tom Thumb. In general, lower alpha-amylase activity was observed at higher germination temperatures. However, the data indicate that the enzyme activity depends to some extent on the ripening temperature conditions. Thus the results indicated that seed dormancy, alpha-amylase activity and kernel weight are determined by the genotype of a variety and influenced by the temperature during maturation and germination of kernels.