Seed Reserves Partitioning and Its Role in Early Vigor of Wheat Seedlings

This experiment was conducted to study the method of seed reserves partitioning and its effects on the early vigor of seedlings of five winter wheat cultivars (Azar-2, Sabalan, Sardari, Alvand and Zarrin) in a completely randomized design during 2004. Results revealed that, seed dry weight (SDW) decreased through the time in all of the cultivars and approximately 7.7-9.7 % of total seed weight (TSW) was formed by structural compounds. Reduction of SDW was continued up to 15- 18.25 days after soaking and later on, the seedling dry weight got an enhanced trend as the seedlings reached to the autotrophy phase. Furthermore, wheat cultivars followed similar style in root/shoot and TLW/TDW ratios. Also, the cultivars were similar in the amount of seed reservesconsumption (89-92%), but were different in the rate of seed resources consumption. Moreover, leaf emergence affected seed reserves partitioning to the other organs. Accordingly, by leaf emergence a peculiar portion of the reserves allocated to this organ. In addition, results showed that the conversion efficiency of seed reserves to the seedling structure ranged 32-68 % in all the cultivars, in which, the maximum and minimum conversion efficiency achieved for Azar-2 and Alvand cultivars, respectively. The noticeable difference among the cultivars from this point of view could be due to the method of reserves allocation to growth and/or maintenance respiration. Also, thegrowth and maintenance respiration of the studied cultivars ranged from 21.9-44.7% to 55-78.1 %, respectively. Based on the results, it could be stated that, there is a direct relationship between conversion efficiency and growth respiration. However, cultivars with the highest growth respiration were usually produced strong seedlings. Among the cultivars, Azar-2 had the highest conversion efficiency, which was significantly different from the others at 5% probability level.Strong early vigor in cereals would cause reduction of herbicide application, enhancement of water use efficiency as well as improvement of transpiration efficiency and finally the yield increase. Among the cultivars tested in this study, Azar-2 showed better early vigor. However, to attain the optimum yield, evaluation of other wheat cultivars is recommended.