Changes Of Agronomic Traits And Physiological Characteristics In Rice Varieties During Genetic Improvement In Jilin Province

Grain yield dramatically increased in genetic improvement of rice cultivars. Rice yield increaseeventually slowed and the average yearly increase in world rice production dropped from 3.7% in 1980s to0.9% in 1990s. In order to break the yield ceiling, the contribution of plant type and physiologicalcharacteristics in yield were paid close attention recently. The different ideotypes of rice were proposed indifferent ecotopes. However, the ideotype and physiological characteristics of rice have not been researchedsystematically in Jilin province. The objective of this study was to determine the ideotype of rice cultivars andraise strategy of high yield breeding and cultivation and changes of yield, agronomic traits and physiologicalcharacteristics were studied on 33 rice cultivars developed from 1958 to 2005 in Jilin province.33 representative cultivars were grown at rice experiment field of Jilin agricultural university andarranged in a randomized complete block design with three replicates in 2006 and 2007. Grain yield, yieldcomponents, agronomic traits and dry matter accumulation, photosynthesis, protective enzyme activities andfluorescence parameter of chlorophyll were studied, the result showed:1. Grain yield were linearly increased from6741.86 kg ha^-1 in 1958 to12178.35 kg ha^-1in 2005, from thecalculation of regression equation with means of two years, the 1.72% annual increase. Rice yield increaseslowed since 1990, only 0.35% per year. There were extremely significant increases in spikelets per panicle,spikelets per square meter and filled spikelets of rice cultivar with year of release; Curvilinear change wasfound between numbers of panicles and year of release, numbers of panicles increased significantly with yearof release before 1990(r=0.63^**) and decreased with year of release after 1990(r=-0.31); there was no changewith year of release in 1000-grain weight. The slowly increase in grain yield with year of release was due tospikelets per square meter increased insignificantly, the reason was numbers of panicles descended. Theincreasing trend in yield of cultivars released before 1990 was mainly due to the improvement in harvestindex (HI)(r=0.73^**), while an increase in total biomass was associated with yield trends for cultivars-linesdeveloped after1990(r=0.68^**). Therefore, further increase in rice yield will through selection higher biomassproduction cultivar, suitably increasing numbers of panicles and spikelets per panicle.2. Plant type had been changed Significantly with genetic improvement of rice. Plant height and stem-leafangle degraded significantly with year of release. Culm node length degraded significantly with year ofrelease, but forth culm node length insignificantly degraded. Cuhn node diameter increased insignificantly.Weight per panicle and panicle-boren rate increased significantly with year of release. Panicle length changedinsignificantly. Heading date postponed significantly and leaf area index(LAI) significant increase after grainfilling stage. Plant height was negatively correlated with both yield and biomass of cultivars released before1990 (-0.67^**, -0.08), while positively correlated after 1990(0.28, 0.12). Accordingly, suitably increasing plant height and culm node diameter, raising weight per panicle and panicle-boren rate, increasing LAI of latergrowth stage were target of super high-yield breeding and cultivating in Jilin province.3. Dry matter production had been changed significantly with genetic improvement of rice. With year ofrelease increasing, biomass before heading stage decreased, while biomass after heading stage rosesignificantly. Dry matter accumulation per day in the whole growth stage increased significantly with year ofrelease. Dry matter production after heading was positively correlated with both yield and biomass. Dryweight per stem decreased in tillering, but increased after heading with year of release and significant increasein milke ripe and maturity. Dry weight per stem after heading was positively correlated with yield andnegatively correlated with tiller numbers. Net assimilate rate of leaf increased with year of release fromtillering to heading, and positively correlated with yield, spikelets per panicle and spikelets per square meter.Therefore, raising net assimilate rate of leaf before heading will benefit to enlarge sink capacity, increasingdry matter production capability will benefit to increase biomass and yield. Dry weight per stem can be act asa index whether or no suitable population structure.4. Photosynthetic characteristics had been changed significantly with genetic improvement of rice. Netphotosynthetic rate (Pn) increased significantly with year of release at grain filling and milke ripe, andchanged insignificantly at heading stage. Pn was positively correlated significantly with apparent mesophyllconductance (Pn/Ci) higher than stomatal conductance (Gs). Prosperity growth period of modern cultivars aregrain filling stage, while older cultivars are heading stage, which concluded from transpiration rate(Tr) andwater usage efficiency(WUE) change. Respond capability Light-Pn and CO₂-Pn of flag leaf of modern ricecultivars higher than that of older rice cultivars. Yield was positively correlated with both flag leaf sourcecapacity (LSC) and leaf area duration (LAD) (0.46^**, 0.41^*). Yield was positively correlated with bothchlorophyll content (Ch1) of flag leaf 20 day and 30 day after heading (0.39^*, 0.43^*), but, correlatedinsignificantly with Pn. Flag leaf soluble protein and sugar were correlated insignificantly with both Pn andyield.Accordingly, Pn and Ch1 of flag leaf can be act as facility index to identify photosynthetic functionalperiod and capability of rice cultivars. Results suggest that further breeding in super high-yield rice willincreasing source on the ground enlarging sink. Supply capability of source were enhanced through screeninglonger photosynthetic functional period and higher Pn and Chl of flag leaf at later growth stage of ricecultivars.5. Leaf senescence rate had difference significantly with genetic improvement of rice. With year ofrelease increasing, malondialdehyde (MDA) content decreased, superoxide dismutase(SOD) andcatalase(CAT) activity increased. PSâ…¡maximum efficiency(Fv'/Fm'), quantum efficiency of PSâ…¡(ΦPSâ…¡),PSâ…¡operating efficiency (qP) and electron transfer rate(ETR) of leaf in the light-adapted were increased withyear of release. Leaf senescence rate of modern cultivars was slower than that of older cultivars. Fluorescence parameters of leaf in the light-adapted can act as identify photosynthetic capability of rice cultivars.In short, our results suggested that the fundamental strategy of super high-yield breeding and cultivationwound been increasing source on the wound enlarging sink. Enlarging sink will occur through suitablyincreasing numbers of panicles, continue increasing spikelets per panicle and raising panicle-boren rate; Inorder to increasing biomass, increases source supply capability will necessary occur through screening longerphotosynthetic functional period, and larger LAI, higher Pn and Ch1 of flag leaf and leaf senescence rateslowed at later growth stage of rice cultivars. Constructing ideotype of super high-yield rice would beenessential way for purpose of the fundamental strategy realized.