| Eight dry-land winter wheat cultivars(Triticum aestivum L.), representative of those widely cultivated from the 1940 s to the 2010 s in Shaanxi Province of China, were selected and grown in field as well as pots during consistent growing seasons of 2010-2014. Irrigation and drought treatments were set, and lab analysis was conducted, so as to identify the morphological and physiological traits associated with yield progress. Yield and yield components, post-anthesis contributes to grain weight of photosynthetic organs, photosynthetic characteristics of leaves and root characteristics were studied, and findings are as follows:1 The yield of dry-land winter wheat in Shaanxi province increased significantly with cultivar replacement. In the field experiment during growing seasons of 2010-2014, the average yield under irrigation and drought treatments of dry-land wheat in Shaanxi province increased from 3278 kg·ha-1 of 1940 s, to 5356 kg·ha-1 of 2010 s, with an annual genetic gain of 0.65%. The increment in irrigation was far more than drought treatment, annual genetic gain was larger.2 The increase of yield in Shaanxi province was consistently and positive associated with the grain weight and harvest index. In the experimental seasons of 2010-2014, aboveground biomass and spike number at maturity were almost stable during the past 80 years of breed improvement in Shaanxi province. With an increase in thousand grain weight and the harvest index, grain yield was improved directly. However, the increasing range of grain yield was limited by the nonideal harvest index. With the significant decrease of grain number and thousand grain weight of the cultivars planted after 1980 s, the grain yield under drought was declined sharply and the genetic gain was under restrictions.3 Pre-anthesis(booting stage) photosynthetic rate of flag leaf and leaf area index increases of modern cultivars were closely related to yield increase, withal post-anthesis photosynthetic characteristics were comparatively less correlated to the yield genetic gains. During growing seasons of both 2010-2011 and 2011-2012, plant height of Shaanxi dry-land wheat was decreased significantly with the introduction of dwarf genes. Height of Cultivar after 2000 s was declined to approximately 80 cm, which had approached to the ideal value. Although the mean tilt angle showed no obvious change with the plant height decrease, leaf area index at booting stage of modern cultivars was apparently higher than old ones. In addition with the photosynthetic rate and area of flag leaves advantage at this stage, modern cultivars possessed obxious superiority for both single leaf and whole canopy. All the traits were beneficial for modern cultiars to accumulate more aboveground biomass before anthesis. A trend over time towards a larger flag leaf area was consistent at 3 and 20 days after anthesis, however with the absence advantage of flag leaf photosynthetic rate and leaf area index, no obvious correlation between post-anthesis photosynthetic characteristics and grain yield was observed.4 Pre-anthesis dry matter translocation efficiency and post-anthesis contribution of ear assimilates increased significantly with cultivar replacement. During growing seasons of both 2012-2013 and 2013-2014, post-anthesis leaf contribution to grain weight showed a slight declining trend with time, while contribution of ear assimilates to grain weight was raised up to more than 50% of modern cultivars, what would contributed to maintain the carbohydrate accumulation when the leaves got senescent. Ahoutgh plant height and stem weight were declined with drawf genes used in the breeding work, pre-anthesis dry matter translocation and translocation efficiency increased with cultivar replacement. Furthermore, ear contributions to grain weight were less influenced by water conditions, meaning it as a more stable source for accumulating carbohydrate. Both advantages before and after anthesis promoted the grain yield increase with breed improvement.5 No obvious trend with time of root characteristics or water consumption characteristics was found with planting decades. Results in 2010-2011 and 2011-2012 field and pots experiments indicated that: although root size at anthesis and maturity fluctuated between decades, no trend with time was observed for root weight, root length, or root surf area. Root length and surf area of cultivars after 2000 s at anthesis might be higher than old ones, however as the increase was mainly concentrate in the surface soil from 0 to 40 cm, no more water consumption was found. With the stable water consumptions between cultivars and the improvement of yield with time, modern cultivars showed an increase in water use efficiency. This might be also the reason for the limitation for water use efficiency increase. In the field experiment, lager root size than irrigation was resulted in by mild water stress in drought treatment. On the other side, severe water stress led to a serious decline in single plant root weight.6 Yield of modern dry-land cultivars were more sensitive to drought stress, root system characteristics sensitivity to water stress at maturity deceased from 1950 to 2010 s. Root weight, length and surf area sensitivity to water stress declined significantly from 1950 to 2010 s, increase amplitude under drought of root size was smaller for modern cultivars. Cultivars after 2000 s showed larger drought decrease amplitude of yield than the other cultivars, a greater variation range between irrigation and drought. The local cultivar planted in 1940 s showed better self-adjustment capacity to water conditions, both grain yield and root system were least sensitive to water stress among all cultivars in the experiment. |
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