Effects Of Paclobutrazol On Lodging Resistance,Photosynthetic Characteristics And Yield Traits Of Rice Under Different Planting Densities

Rice（Oryza sativa L.）,as an important food crop,plays a vital strategic role in ensuring domestic food security.Regulating density is one of the main cultivation techniques to optimize population structure and increase yield.Plant growth regulators play an important role in improving plant agronomic traits and enhancing stress resistance.Therefore,regulating the relationship between planting density and growth regulators is an important technical measure to ensure high yield of rice.This study was conducted in Jinsha farm,Xinxing District,Qitaihe City in 2020.Using the rice variety"Longjing 57"as the experimental material,under the conditions of setting three different planting densities(200000,250000 and 333000 holes·hm^-2),three different concentrations of paclobutrazol(500,1000 and 1500 g·hm^-2)treatment,with paclobutrazol as the control treatment,to explore the effects of paclobutrazol on rice agronomic traits,lodging characteristics,photosynthetic characteristics and yield under different planting densities,aiming to provide theoretical basis and technical reference for high-yield rice cultivation techniques.The main results are as follows:（1）The plant height and LAI of rice showed a gradual increase trend as the planting density gradually increased,while the dry matter accumulation above the ground showed a trend of first increasing and then decreasing.Under the condition of 1500 g·hm^-2paclobutrazol,the plant height,LAI and dry matter accumulation of rice all showed a downward trend.The results of variance analysis showed that the effects of paclobutrazol treatment on plant height,LAI and dry matter accumulation were significantly lower than planting density.In the booting stage of rice,paclobutrazol treatment had no significant effect on plant height,but had a very significant effect on LAI and dry matter accumulation.（2）With the increase of planting density,the gravity height of rice and the length of the second and third internodes at the base showed a gradual increase,while the thickness,bending resistance and bending moment of the second and third internodes showed a downward trend.1500g·hm^-2paclobutrazol can significantly reduce rice plant height,shorten the length of internodes,increase the thickness of the internodes at the base of the stalk,and increase the bending resistance and bending moment of the stalk.Planting density and paclobutrazol treatment both significantly affected the morphological characteristics and mechanical properties of the stalk,but had no effect on the culm lodging index.（3）The planting density of 333,000·hm^-2significantly reduced the SPAD value of rice leaves and the intercellular CO₂concentration,and increased the P_n,T_rand G_s.The SPAD value,P_n,T_rand G_sof rice leaves were all increased after applying paclobutrazol at different concentrations,and the effect on the intercellular CO₂concentration was not significant.The analysis of variance showed that both planting density and paclobutrazol treatment significantly affected the photosynthetic capacity of rice leaves.At the maturity stage,both planting density and paclobutrazol treatment had no significant effects on the gas exchange parameters of rice leaves;while paclobutrazol treatment significantly affected the SPAD value,P_n,T_rand G_sof rice leaves at the booting stage.（4）With the increase of planting density,the panicle length,effective panicle number,grain number per panicle,seed setting rate and yield of rice showed an increasing trend,and the impact on the thousand-grain weight was not significant.1500 g·hm^-2paclobutrazol can reduce the panicle length and grain number,increase the effective panicle number,seed setting rate and yield of rice.The analysis of variance showed that the effect of planting density on panicle length,effective ear number,grain number per ear,seed setting rate and yield was significantly higher than that of paclobutrazol treatment.This study found that the main factors affecting the yield of rice when combined with paclobutrazol under different planting densities are the number of grains per panicle and the number of effective panicles.In summary,when the planting density of rice reaches 333,000 holes·hm-2,the application of1500g·hm-2 paclobutrazol can significantly regulate plant agronomic characteristics,photosynthetic characteristics,lodging characteristics and yield characteristics.