Effects Of Drought Stress At Tillering Stage On Yield Formation Of Japonica Rice In Cold Region

Heilongjiang Province is the main producing area of high-quality Japonica rice in cold region of china.Seasonal drought is frequent,and the area of rice has developed rapidly.So the water shortage has became one of the main restricting factors.Tillering stage is the key period of rice population quality,nutrient accumulation and effective panicle number formation,which is an important prerequisite for high yield of rice.The drought stress at tillering stage may cause the color of leaf turn pale,growth retardation,and the decrease of plant height,tiller number,photosynthetic efficiency,effective panicles,grain number,seed setting rate and yield.However,in the actual production,it is more effective to control the occurrence of ineffective tillers in the later stage of tillering,which shows that the irrigation water amount is reasonable and has a great potential for water saving.Therefore,the study of yield formation mechanism of Japonica rice in cold region under drought stress at tillering stage has a great significance.So the Songjing 6(drought-sensitive)and Dongnong 425(drought-tolerant)was selected as test materials,then set three drought gradient(mild drought,-10kpa;moderate drought,-25kpa;sever drought,-40kpa),Compared with normal irrigation.The yield formation rules of Japonica rice in cold region under drought stress was revaled from the aspects of growth,photosynthetic characteristics,dry matter accumulation and distribution,grain filling characteristics and yield formation.Find out the mechanism of yield formation of Japonica rice in cold region under drought stress.The aim is to enrich the physiological basis of drought resistance of Japonica rice in cold region.In order to provide theoretical basis for the establishment of water saving cultivation techniques of Japonica rice in cold region.The main results of this study are as follows:1.The plant height and it's growth rate of the two tested varieties(Songjing 6,Dongnong 425)were all decreased with the soil water potential at tillering stage,and the A2 and A3 treatments decreased significantly.Drought stress also significantly inhibited the occurrence and growth of tiller,resulting in the significant decrease of tiller growth rate and the highest tiller numbers,the date of tillering peak was delayed,and the degree of influence increased with the soil water potential.The leaf area of different growth stages in Japonica rice in cold region all significantly decreased.In terms of the degree of influence,the drought stress in tillering stage had the greatest effect on the leaf area,followed by the tiller number,and the effect on plant height was relatively small.As for varieties,the decline of the 425 treatments was all less than Songjing 6,which indicated that the effect of drought stress was greater in Songjing 6.2.The drought stress at tillering stage caused a significant decrease of the total chlorophyll content,chlorophyll a/b ratio,but the carotenoids content was opposite,and the differences between different treatments have reached a significant level.The Pn,Tr,Gs and Ci of two tested varieties all significantly decreased with the soil water potential.It can be seen that the photosynthetic parameters and the changes of the content of photosynthesis are synchronous.It can be concluded that the main reason for the decline of photosynthetic parameters of Japonica rice in cold region under drought stress is the decrease of photosynthetic pigment content.As for the drought treatments,the A1 treatment of Dongnong 425 was the most close to the control level.In terms of varieties,the decline of drought treatment of Dongnong 425 was less than that of Songjing 6.3.The drought stress at tillering stage caused a significant decrease of total dry weight,dry matter accumulation of each organ in the shoot,translocation and contribution rate of stem and leaf.The decline was increased with the soil water potential,and there were significant differences between varieties and treatments.Among them,the desrease of dry matter accumulation in tillering and booting stage of cold-region under drought stress was the most significant,and the ratio of dry matter accumulation in tillering and booting stage in the maturity was up to forty percent.At the same time,the Tmax,D,R0,GRmax,GRmean alldecreased with the soil water potential under the drought stress at tillering stage.Oveall,the effect of Dongnong 425 was less then Songjing 6 under drought stress at tillering stage.In addition,the A1 treatment of Dongnong 425 was closest to the control level.The two tested varieties were all affected by drought stress,but the influence degree of Songjing 6 was greater,while that of Dongnong 425 was relatively small.4.The yield was decreased with the soil water potential under the drought stress at tillering stage.Among them,the DRE and DEC of mild treatment of Dongnong 425 was 0.96 and 1.12,and there was no significant difference between the mild drought treatment and CKin Dongnong 425.It means that the mild drought treatment of Dongnong 425 had a stronger advantage.So,the-10 kpa treatment of Dongnong 425 is more suitable for the practical application of water saving irrigation in tillering stage.When the soil water potential was-25 kpa to-40 k Pa,the yield of two tested varieties decreased significantly.The drop of yield was mainly caused by the decreased of spike number,kernel number and seed setting rate.Correlation analysis showed that the dry matter accumulation of heading and maturity stage,translocation volum,translocation rate,contribution rate of stem and leaf,spike number,kernel number,seed setting rate,1000-grain weight were all extremely significant positive correlated with the yield.