| Drought is one of the most serious limiting factors for crops growth and production,which occurs more frequently,intensively,and widely.Rice is the most important cereal crop in China,it is the staple food for half of the population.In recent years,drought is the most serious limiting factor limiting rice production worldwide and is becoming more intense with climate change.In the last century,the yield potential of rice increased gradually with rice variety released frequently.Pursuiting high yield is the main target for rice breeding and genetics in historical rice varieties evolved in the last century.However,so far little attention has been given to the temporal changes of drought resistance concomitant with the year of release in rice genetic breeding.And how does the drought resistance of rice varieties change with genetic breeding is still unclear.Therefore,the screening and breeding drought-tolerant rice genotypes are essential to maintain yield gain and ensure food security under adverse environments.Sixteen rice genotypes bred or widely cultivated from 1934 to 2007 were grown in paddy fields(Control,CK)and upland fields(drought stress,DT)to explore the variation of drought resistance in rice genotypes with the year of release.The experiment was carried out in a completely random block design with 4 replicates and a plot area of 30 m2 to explore the yield performance,yield formation characteristics and variation characteristics of drought resistance in the succession process of historical rice varieties under normal water and drought stress.The main results are the following1.The yield and daily grain yield of historical rice varieties increased significantly with the development of the succession process.The increase of rice yield in the process of genetic improvement was mainly attributed to the significant increase in panicle number,grains per panicle and grain filling percentage.In addition,various growth-related characteristics like biomass,harvest index,relative growth rate,grain density and growth duration increased with an increase of genetic refinement of the genotypes through the years,and they contributed to improvement of final rice yields.2.Rice yield,yield components,and growth-related indicators declined sharply under drought stress.The correlation analysis showed that grain yield was positively correlated with panicle number,spikelets per panicle,grain filling percentage,biomass,harvest index,relative growth rate and grain density significantly with the progress of rice genetic breeding.It was worth noting that the correlations of grain yield with panicle number,spikelets per panicle,biomass,harvest index and relative growth rate were decreased sharply under drought stress.It is suggested that these parameters are sensitive to drought stress3.Drought resistance coefficient(K)is the ratio of each parameter under normal condition to that under drought condition.The drought resistance coefficients of KYield,KDaily grain yield,KPanicle number,KSpikelets per panicle,KBiomass,KPlant height,KRelative growth rate and KFilling percentage prominently improved by genetic breeding.Drought resistance of rice genotypes has been significantly enhanced by genetic processes during the past 73 years in China,but they are still sensitive to drought conditions.Currently,there is still room for further improvement in drought resistance which is an important target in future breeding programs. |
