| The spring wheat(Triticum aestivum L.)is the main food crop and very important to the life of smallholder families,whereas its grain yield is low and unstable due to the variation of annual precipitation.There are two features for wheat breeding and cultivation in semiarid areas of Loess Plateau:(i)new breeding wheat cultivars are planted in limited field and not successful to replace the old wheat cultivars,as old wheat cultivars are still used in field;(ii)the farmers in semiarid regions would balance the grain yield and yield stable of each wheat cultivars,while they select which cultivar will be sowing in their field.The 18 spring wheat cultivars were used in this field studies with similar growth period.The field experiments were conducted in semiarid regions,Yuzhong(2015 and 2016)and Dingxi(2016)in Gansu Province,respectively.In 2015,all plots in Yuzhong were irrigated with 60 mm rap water 20 days after sowing,whereas there were no irrigation for both Yuzhong and Dingxi in 2016;Therefore,there were three variation precipitation for Yuzhong in 2015,Yuzhong and Dingxi in 2016,with different precipitation of 227,205 and181 mm during the spring wheat growing season(March-July),respectively.The aim of this study is trying to clarify the linkage among grain yield and component,phenological period and yield stable,as well as reproductive and vegetative biomass allometric relationship(R-V relationship)for 18 spring wheat cultivars.The main results of this study as follows:(1)The three kinds of accumulated temperature(of 10?,5?,0? or more)for heading,flowering and maturity are used to analyze the performance of all spring wheat cultivars in three environments,which show that there are significant difference among cultivars,environments and the interaction between cultivars and environments(P<0.001).The accumulated temperature of heading,flowering and maturity in Yuzhong of 2015 is the lowest,but in Dingxi of 2016 is the highest.The cutivars(NABUQ-6)with lower accumulated temperature in growing season were found with lower accumulated temperature in heading and flowering;The cutivars(Jinbaoyin)with higher accumulated temperature in growing season were found with higher accumulated temperature in heading and flowering.(2)The grain yield,aboveground biomass and harvest index are significant difference in cultivars,environments and the interaction between cultivars and environments(P<0.001).Thegrain yield and aboveground biomass in Yuzhong of 2015 is the lowest,but in Dingxi of 2016 is the largest.Therefore,the highest grain yield cultivar(Dingxi 35)in most precipitation environment(Yuzhong,2015)was not the best one in the least precipitation condition(Dingxi,2016);in addition,the highest grain yield cultivar(Zhonghan 1)in least precipitation environment(Yuzhong,2015)was also not the best one in more precipitation condition.(3)The correlation analysis between grain yield and agronomy parameters of all spring wheat cultivars in both environments showed that there were significant positive correlation between grain yield and aboveground biomass(R=0.97,P<0.001),harvest index(R=0.52,P<0.01),1000-kernel weight(R=0.44,P<0.01),grain number per kernel(R=0.75,P<0.001),plant height(R=0.54,P<0.001),flag height(R=0.40,P <0.05),spike length(R=0.49,P <0.01)and precipitation during growing seasons(R=0.84,P<0.001).The cultivars with early heading,flowering and maturity time(days after sowing)were beneficial for the grain yield formation,while the grain yield were significant negatively correlated with accumulated temperature of heading(R=-0.57,P<0.001)and flowering(R=-0.50,P<0.001),but were not significant correlated with growing season(R=0.12,P>0.05).The path analysis further indicated that the main parameters which affect the grain yield improvement were aboveground biomass,harvest index and spike number per square meter,these three main parameters could account the 99.1% the grain yield variation in this study.The path coefficient of aboveground biomass,harvest index and spike number per square meter are 0.910,0.264,0.036,respectively.(4)The grain yield and stable analyse of all the spring wheat cultivars by GGE(genotype main effects and genotype by environment interaction effect model)biplot and well-posedness parameter show that the grain yield is not harmonize with yield stable,in other word,the lower grain yield,the higher stability;the better grain yield,the lower stability.We selected the grain yield and stable as parameter to classify 18 spring wheat cultivars into three groups:lowest yield but highest stable cultivars(Lantian,DURRA-5,Ganhan 3,Dingxi 24,Heshangtou,Longchun 26 and Xihan 2),higher yield and higher stable cultivars(DAIRA-12,Zhonghan 1,Longchun30,Zhonghan 4,Ganhan 5 and Jinbaoyin),highest yield and least stable(Dingxi 35,Dingxi43-4,NABUQ-6).(5)The allometric relationship between reproductive(grain yield)and vegetative biomass of spring wheat cultivars in three environments show that the precipitation causes the difference between plant size and reproductive output,and vegetative biomass can explain more than 83%variation of grain yield.The allometric index between reproductive(grain yield)and vegetative biomass in all of the lowest yield but highest stable cultivars were significantly lower than 1,whereas in the entire highest yield but lowest stable cultivars were significant higher than 1.In thehigher yield and higher stable cultivars,The allometric index between reproductive(grain yield)and vegetative biomass have three kinds of significantly relationship with 1,lower than 1(021-128,Jinbaoyin and Zhonghan 4,P<0.001),equal 1(Ganhan 5,Longchun 30 and Zhonghan1,P<0.001),more than 1(DAIRA-12 and Longchun 23,P<0.001)In summary,the results of this study indicate that the grain yield of spring wheat cultivars vary with the precipitation in growing season in the semiarid regions of Loess Plateau,the high grain yield could be guaranteed by high aboveground biomass accumulation,and also high plant height and flag node height.It is a huge challenge for high grian yield wheat cultivar breeding with high yield stability in semiarid environment,while the different directionbetween high grian yiled and high yield stability as showed in this study.It can be understand by people why the new breeding wheat cultivars are planted in limited field and not successful to replace the old wheat cultivar.We speculated that the high yield wheat cultivar allocating more biomass reproductive oragns,as allometric index between reproductive and vegetative biomass is significantly more than 1,may reducing the biomass accumulation in vegetative organs(i.e.the organs with resource accquirement),lead to the low yield stability in cultivars with high grain yield.The allometric analysis between reproductive and vegetative biomass could explain the mechanism why highe grain yield is not harmony with stable in semiarid environment. |
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