Evolution Of Plant Type And Ecological Adaptability In Different-ploidy Wheats Under Drought Stress

Pot-culture and water-control experiments were conducted to determine the changes in plant type and yield formation using six wheat varieties with evolutionally genetic relationship as experimental materials including four wild relatives (Diploid wheat MO1 and MO4, Tetraploid wheat DM22 and DM31), and two hexaploid wheat including old hexaploid Monkhead and modern hexaploid Longchun 8275 which was released in 1998 under the conditions of rain shelter. By analysing the plant type evolution and its relationship with yield formation in different-ploidy wheats under drought stress and sufficient water supply. A few major conclusions were made as follows:1. The data indicated that the leaf angle against stem, the leaf opening angle, the leaf camber and the leaf area tended to increase with the multiplication of chromosome sets, while the length-to-width ratio of leaf was found to decrease. This trend was more distinct under well watered condition. The yield per pot and the yield stability were increased along with the evolvement of wheat varieties. The results showed that dryland wheat was developed to avoid intraspecific competition and enlarge the leaf area to capture sunlight at the level of population by way of increasing blade angle, broadening and shortening blade dimension, which would help improve the population yield as an evolutionary strategy. Experimental results demonstrate the mutually beneficial nature of modern wheat at the individual level and the property of artificial populations.2.Along with the growth of chromosome complement, wheat plant showed decreased branch number,increased stem length. The stem length increases in two ways, one is to increase the length of internode, and the other is to add pitch number. All different-ploidy wheats emerged tillers that have four internodes,five internodes,six internodes, and wheat plant with four internodes is nearest the Golden section index of plant height-0.618, followed by type of five internodes and then type of six internodes. To drought stress group, this kind of effects is sharper. It is believed that wheat plant build ideal Golden section to fulfill its high yield under sufficient water supply, this proportion is broken down under drought stress, whereas wheat with different diploid have different ability to recover and rebuild this proportion. It is obvious that modern wheat plants are superior to wild wheat plants in this direction. Wheat height evolution is not only an active way to adapt to natural selection, but also the result of artificvial selections with a view to increasing crop yields.3. Tactic difference of the golden proportion. The Golden proportion of modern varieties'internodes appear deviate under sufficient water supply, deviation value is between 8.23% and -60.33%, but to varieties under drought stress, there is a big gap between their deviation value and steering capacity. The research shows deviation value of modern varieties is between-5.48% and -19.09%, the value of wild species fall in between -32.91% and -12.34%(diploid) or between -26.05% and -53.47% (tetraploid). Plant height of wheat is increasing as its multiple increase under drought stress, stem height increasing from diploid plant to tetraploid plant is adaptive evolution of natural selection, nevertheless, stem height increasing from tetraploid plant to hexaploid plant is the result of artificial selection aimed volume of production.4. Grey analysis results indicated that the correlation of tillering number to yield was the lowest, but that of plant height to yield relatively high both in CK and S groups, suggesting that dryland wheat was evolved following the tendency of "lower tillering rate, higher plant height" along with the progress from diploid to hexaploid. Biomass of three kinds of main photosynthetic leaves (flag leaf, top 2nd leaf and top 3rd leaf) were observed to wholly share higher correlation to yield than their location height, showing that the effect of leaf biomass was superior to its spatial location effect. Specially, it was first found that the cross sectional area of bottom stem had the highest correlation rate to yield in CK group, but it was ranked last but one in S group. The evidence showed that this trait was likely to be a sensitive indicator of yield formation as a result of drought stress, which was substantial and structural basis of yield formation.5. The comparation of wheat plant pieces between different speed growth:Except very few pieces, different wheat grain yield and the biomass above-ground, leaf weight and ground biomass, the biomasses and tiller development exist allometry-relationship, the allometry-relationship can be showed with y=a+bx Compared with wheat under dronght stress, the grain weight and biomass growth rate of diploid wheat is not obvious under sufficient water supply, as it is not to hexaploid. For all three ploidy types, regulation of allometric growth between leaves weight and the biomass above-ground is obvious; Diploid tillering and the biomass above-ground is more noticeable under sufficient water supply, the others breed is not distinct, and tends to coordinate.