Evaluation On Plant Type Characteristics And Its Relation To Phenotype Evolution In Different Ploidy Wheats

Since Donald proposed the ideotype theory in 1968,changing wheat type to improve its production has become a hot issue in the fields of ecology,crop cultivation and breeding science,theory of evolution and so on.The ideotype-oriented breeding program provided a theoretical basis for breeding strategies and cultivation management innovation in dryland wheat.In previous studies,some progresses have been achieved in revealing plant type evolvement and biomass distribution characteristics in dryland wheat,yet these are still limited for crop germplasm evaluation.A critical restriction is that hexaploid wheat genotypes have been much more studied than diploid and tetraploid ones in existing researches.Most of experimental results were not mutually supportive or even contradictive,which frequently led to a failure for view integration and general understanding.It is so far in a low progress for the fundamental scientific question about plant types change and biomass allocation during the evolution mentioned above.Systemic evaluated the germplasms in different ploidy levels and types are needed to explore the trends of plant types and its related eco-physiological traits.To explore the trends of the plant types,gas exchange parameters,biomass allocation and yield during the wheat evolution,we selected 47 wheat varieties which belong to 11 species in different ploidy levels,and conducted the experiment in the field conditions in the arid and semi-arid region of the Loess Plateau,China.In addition,according to Vavilov law,18 varieties with evolutionary genetic relationships were selected,and each ploidy wheats included 6 varieties and studied the evolution of characteristics and yield in wheat evolution process.Major conclusions as followed:1.During the process of the ploidy levels increasing and artificial selection,the plant height,canopy biomass density and leaf angle decreased,while the leaves traits became more longer and wider.During the domestication process from the wild species to the cultivated species,the plant height in cultivated species decreased by 7–10%in comparison with the wild species.There was a big variation of the plant height in tetraploid level.In hexaploid level,the plant height in the modern cultivated species decreased by 8–10%in comparison with the original hexaploid species T.spleta.Compared with the diploid wheat species,the plant height were significantly decreased in tetra-and hexaploid wheat species（P<0.05）,while there was no significant difference between the tetraploid and hexaploid wheat species.Under the domesticated process,the leaf area of cultivated species was 11–42%higher than the wild species,and the modern hexaploid wheat species was 42–48%higher than the original hexaploid species.With the ploidy levels increased,the leaf area was significantly increased（P<0.05）,and the leaf length-to-width ratio in cultivated species was decreased by 13–24%in comparison with the wild species.However,the leaf length-to-width ratio in modern hexaploid species were increased by 15–27%,compared with the original hexaploid wheat species.The leaf length-to-width ratio in tetra-and hexaploid wheat species were significant higher than in the diploid wheat species（P<0.05）,while there was no significant difference between the tetraploid and hexaploid species.The tiller number was reduced by 25–42%in cultivated wheat species.In hexaploid species,the tiller number in modern cultivated species was reduced by 16–31%in comparison with the original hexaploid wheat species.Totally,with the ploidy levels increased,the tiller number was significant decreased（P<0.05）.The study of 18 different ploidy wheat varieties founded that plant height of hexaploid wheat is significantly higher than that of diploid and tetraploid wheat.With the evolution of wheat,the leaf length to width ratio of tetraploid and hexaploid were significantly higher than that of diploid wheat（P<0.05）,and with the ploidy level increased,the tiller number of wheat was significantly decreased（P<0.05）.In addition,the canopy density of wheat showed a decreasing trend with the increase of ploidy.The results showed that with the process of wheat evolution,the population of wheat was changed into the low plant height aspect,the mass density and metabolic efficiency were significantly improved.2.The photosynthetic parameters of wheat showed different changes with the evolution of wheat.In the diploid and tetraploid levels,the photosynthetic ratio（Pn）in cultivated species was reduced by 12–26%,the stomatal conductance（gs）was reduced by 10–11%,and the transpiration rate（T）was reduced by 13–22%,in comparison with the wild species,respectively.In the hexaploid level,the Pn in modern cultivated species was reduced by 7%,the gs was reduced by8%,and the T was reduced by 6%,in comparison with the original hexaploid species,respectively.For the intercellular CO₂ concentration（Ci）,there was no significant difference among all the species,and the value was approximately 250?mol·mol^–1.The study of 18 different ploidy wheat varieties showed that with the wheat evolution,stomatal conduction and transpiration rate of flag leaves at flowering stage were significantly reduced,but stomatal conductance of tetraploid and hexaploid wheat was no significant difference.Transpiration rate and intercellular CO₂ concentration were decreased and then increased with the evolutionary process.3.With the wheat evolutionary process and under the pressure of artificial selection,the yield production increased by 54–65%,thousand kernel weight（TKW）increased by 61–75%,grain number per plant decreased 5–6%,and spikle number per plant decreased by 55–57%in comparison with the diploid wheat.Through the comparative analysis of 47 wheat varieties,wheat yield increased by 36%–30%compared with wild wheat and cultivated wheat,and the yield of modern cultivated wheat was 74%–97%higher than original cultivated wheat.In the diploid and tetraploid levels,the thousand kernel weight（TKW）in the wild species was significant lower than the cultivated species（in diploid:15.55 vs.20.69,P<0.05;in tetraploid:22.22 vs.32.70,P<0.05）.In hexaploid level,the original hexaploid wheat T.spleta had the lowest thousand kernel weight（TKW）,and the modern cultivated species had the highest TKW values.Analysis of 18 different ploidy wheat genotypes showed that,with its evolutionary process,the yield was increased and there was no significant difference between the tetraploid and hexaploid wheat.However,the tiller number,grain number and spikelet number per ear were significantly decreased.For the thousand kernel weight,it showed increased and then decreased trend.In addition,there was a positive correlation relationship between the individual plant scale photosynthetic rate and the yield（P<0.001）.With the ploidy level increased,the value of slope between the photosynthetic rate and yield also increased,the results showed that higher ploidy level has higher assimilation transfer efficiency.During the domestication process from the wild species to the cultivated species,and with the ploidy levels increased,the biomass that distributed into the ear showed increased trends.Analysis of 47 different wheat germplasms and the results showed that:with the evolutionary process of the wheat,there was an increased trend in the unit stem weight,unit stem diameter weight and the total aboveground biomass.For the tetraploid and hexaploid wheat,the aboveground biomass increased by 17–21%,ear biomass increased by 40–46%,the leaf area increased by 43–67%and sheet biomass increased by 16–22%,compared with the diploid wheat.However,there was no significant difference between the stem biomass among the wheat genotypes.The correlation coefficient value of the vegetative biomass（V）and the reproductive biomass（R）was increased with the wheat ploidy levels increased.Furthermore,the value was significant smaller than 1,Results showed that the allometric relationship was found in the R-V,and the ear biomass was increased with the evolutionary process.Under the dual pressures of nature and artificial selection,wheats gradually evolved to morphological and physiological characteristics,which highly adapted to local climatic conditions.However,different ploidy wheats have big differences of adaptive characteristics to the external environment,and its type evolution and biomass distribution pattern are different too.There are 11wheat species were used as the materials in this study,which included diploid wheat（T.boeoticum and T.monococcum）,tetraploid（T.dicoccoides,T.dicoccum,T.durum,T.turgidum and T.Polonicum）and hexaploid（T.Spelta,T.compactum,T.sphaerococcum,and T.aestivum）,which concluded 47 wheat genotypes.We focused on the ploidy levels（diploid,tetraploid and hexaploid）and wheat types（wild and domesticated）,and concluded that the trends of plant type,biomass,gas exchanges parameters and yield changes during its evolutionary process.It is meaningful for us to understand the mechanism to adaptive the environment of wheat.We pointed out that ideotype-oriented breeding methods is one of the most important breeding methods in the future.