The Relationships Among Competitive Ability, Productive Performance And Density Of Spring Wheat In Semiarid Regions

Donald's ideotype mainly derived from the fact that natural selection act at maximizing individual fitness resulting in more resources were transported into the productive organs, such as stems and leaves for light, root for soil water and nutrients. As a consequence, at the expense of more resources used to the organs for the increase of competitive ability, the resources invested to the reproductive organs were reduced under the environmental conditions with limited resources. The process of natural selection for optimizing individual fitness is the reason that why cultivars degeneration occur. Based on the process, Donald has strongly proposed that cultivars can improve communal performance by decreasing competitive ability and increasing harvest index of seed crop cultivars. Donald's ideotype did get some success in cultivars breeding. But there are some evidences that support that cultivars with strong competitive ability can perform better than that of the cultivars with weak competitive ability. Curtailing competitive ability must gain high yield? Is the relationship between competitive ability and seed yield negative correlation?de Wit replacement series experiments were conducted to determine the relative competitive ability and grain yields of four spring wheat cultivars, which include landrace Heshangtou and the modern cultivars Longchun-8139, Dingxi-24 and Gaoyuan-602. Cultivars were grown in pairwise mixtures and were compared with monoculture. The experiments were conducted in 2005 and 2006 at the semiarid area of Loess Plateau, Gansu province, China. The results were not completely consistent between two years. In 2005, Dingxi-24 had highest competitive ability, followed by Heshangtou, Longchun-8139 and Gaoyuan-602, while seed yield ranged from the cultivars of Dingxi-24, Longchun-8139, Gaoyuan-602 to the landrace Heshangtou in a decreasing order, but there is no significant yield difference between Gaoyuan-602 and Heshangtou. The results showed that the cultivars with higher competitive ability produced lower seed yields when we compared Heshangtou and Lonchun-8139, When four combinations among Dingxi-24, Longchun-8139 and Gaoyuan-602 in pairwise, Dingxi-24 and Heshangtou by comparison showed that cultivars with higher competitive ability had higher seed yield. The results showed that natural selection aiming at maximization of individual fitness by increase in competitive ability resulted in growth redundancy, with the more resources being invested into the competitive organs at the expense of the reproductive organs. The implications are that shifting resources into reproductive organs by reducing competitive ability through crop breeding can increase wheat production under certain environments, which is consistent with Donald's ideotype. The reverse results revealed that if more resources were simultaneously invested into reproductive and competitive organs, the bred varieties can also perform better than varieties with lower competitive ability.In the year of 2006, Heshangtou had the highest competitive ability, followed by Dingxi-24, Longchun-8139 and Gaoyuan-602 in a decreasing order, but productive performance is no significant difference because of low rainfall.Density experiment showed competitive ability and optimal density is negative correlation. The cultivars with low competitive ability will maximize yield at high density because of low interference between plants.Our results indicate there are three kinds of relationships between competitive ability and yield. So we can conclude that competitive ability is not necessarily correlated with seed yield and the key to increase yield is to develop cultivars with higher harvest indices and aboveground biomass. Wheat breeding not only in arid and semiarid areas but also in humid areas should focus on the improvement of both harvest index and increase of aboveground biomass.