Effects Of Planting Density On Yield Formation And Rice Quality Of Perennial Rice Yunda 107 Under Twice Harvest One Year Scheme

Perennial Rice has been successfully bred via the clonal propagation characteristics of rhizome of Oryza longistaminata.Perennial rice Yunda 107（hereinafter referred to as Yunda 107）is planted in twice harvest one year scheme in production and application.However,there is no clear evidence for the optimal planting density of twice harvest one year scheme of perennial rice,which has affected the formulation of cultivation techniques for perennial rice.In order to clarify the influence of cultivation density on the growth,yield and quality of perennial rice,a field trail was applied under twice harvest one year scheme（two seasons a year,after early rice harvest,tillers ratoons from the rhizome of rice stalks）in Menghai County where is the major production area of perennial rice in 2019,Yunda 107 was selected as the material,five planting densities with three replicates were set up,the five planting densities were D1（16.50 million plants/hm²,16.5 cm×50 cm）,D2（21.00 million plants/hm²,16.5 cm×40 cm）,D3（25.50million plants/hm²,16.5 cm×30 cm）,D4（30.00 million plants/hm²,16.5 cm×28 cm）and D5（34.50 million plants/hm²,16.5 cm×25 cm）,respectively,to study the effects of cultivation density on the tillering characteristics,photosynthetic characteristics,dry matter accumulation characteristics,yield and yield composition and rice quality of Yunda 107 under twice harvest one year scheme,the optimal cultivation density of Yunda 107 was determined,and Provide basis for high-yield and high-quality cultivation techniques of perennial rice.The results were as following:1.The planting density significantly affected the effective panicle number,panicle formation rate and rice pile survival rate of Yunda 107.Season（P<0.05）and density（P<0.01）had significant effects on the effective panicle number of Yunda 107,it showed a downward trend as the density increased,the highest effective panicle number were in D1 and D2 for early rice and late rice,20.50/hole and 18.60/hole respectively,and that for early rice（16.60/hole）was significantly higher than late rice（13.92/hole）.Season（P<0.01）,density（P<0.05）and the interaction effect of season and density（P<0.05）had significant effects on the panicle formation rate of Yunda 107.The panicle formation rate of early rice was significantly different with late rice.For early rice,D4and D5 treatments was higher with an average value of 93.47%;but that of late rice decreased with increased density,and the highest value was D1 treatment（84.53%）.Density had a significant effect on the survival rate of perennial rice（P<0.05）,which decreased with the increase of density,the highest value was D1 treatment（92.81%）.2.The effect of planting density on photosynthetic characteristics of Yunda 107.Season,density and the interaction effect of season and density extremely significantly（P<0.01）affected the SPAD of Yunda 107 at 15 days after heading stage and the maturity period（except the interaction effect between season and density at 15 days after heading stage）.The SPAD showed a downward trend with the increase of density at15 days after heading stage.The highest level for early rice and late rice were D2（28.30）and D1（39.77）respectively,and that of late rice（37.47）was slightly higher than that of early rice（27.11）.The SPAD decreased with the increase of density at maturity,the highest level for early rice and late rice were D2（35.55）and D1（28.00）,respectively,and early rice（34.05）was higher than late rice（24.29）.Season（P<0.01）,density（P<0.05）and the interaction effect between season and density（P<0.01）had significant effects on the stomatal conductance and the intercellular CO₂ concentration（P<0.01）of Yunda 107 during mature period.The stomatal conductance and intercellular CO₂ concentration of early rice increased with increasing density to D3(0.84 mol·m^-2·s^-1,369.17μmol·mol^-1)and then decreased,while the highest stomatal conductance for late rice was D4(0.34 mol·m^-2·s^-1),the highest intercellular CO₂concentration was D2(375.72μmol·mol^-1).3.The effects of planting density on the dry matter accumulation of Yunda 107.Season,density and the interaction effect of season and density had significant effect on the dry matter accumulation of a single plant of Yunda 107 from heading stage to maturity（P<0.01）,and it showed a downward trend as the density increased,D1treatment showed highet values for both early and late rice（71.44 g/hole and 25.66g/hole）at heading stage.At 15 days after heading,the highest levels for early and late rice were in D2（72.79 g/hole）and D1（48.97 g/hole）,respectively.While at maturity,the highest levels for early and late rice were both in D1,were 108.39 g/hole and 74.62g/hole,respectively.Moreover,the dry matter accumulation of individual plants and group of early rice（56.32 g/hole and 1332.73 g/m²）was significantly higher than that of late rice（37.43 g/hole and 779.89 g/m²）,this is one main factor why the grain yield of early rice was higher than late rice.4.The effects of planting density on the yield and yield components of Yunda 107.Season,density and the interaction effect of season and density had significant effects on the yield of Yunda 107（P<0.01）.The yield of late rice（3.26 t/hm²,4.38 t/hm²）was lower than that of early rice（8.92 t/hm²,7.69 t/hm²）.The yield of early rice and late rice showed an increased trend and then a decreased trend as the density increased.The highest measured yield was D2（11.67 t/hm²）and D3（3.63 t/hm²）for early and late rice,respectively,and the highest theoretical yield was both in D2 treatment（8.56 t/hm²,4.56t/hm²）.The yield of Yunda 107 was positively related with the effective panicles,panicle formation rate,SPAD at maturity,stomatal conductance at maturity,intercellular CO₂ concentration at maturity and the dry matter accumulation from heading to maturity,which illustrated the tillering,photosysthsis and dry matter accumulation characteristics significantly affected the yield of Yunda 107.5.The effect of planting density on the rice quality of Yunda 107.Season had significant effect on roughness and milled rice rate of Yunda 107（P<0.01）,grain length（P<0.05）and chalkiness（P<0.01）,amylose content and gel consistency（P<0.05）.The rice quality of late rice was superior to early rice,which was mainly manifested in three aspects,the head rice rate of late rice（60.99%）was significantly higher than that of early rice（27.97%）;chalkiness（5.43%）was significantly lower than that of early rice（6.40%）;amylose content（16.34%）was significantly lower than that of early rice（16.70%）.Cultivated density had significant effects on the percentage of polished rice,chalky grain rate,chalkiness and amylose content（P<0.01）.The rate of polished rice decreased with the increase of density,D1 had the highest levels for both early and late rice,were 44.10%and 62.87%,respectively.The chalky grain rate and chalkiness decreased with density and then increased and then decreased.The chalky grain rates of early rice and late rice were lowest both in D3 treatment,were 26.00%and 26.67%,respectively.Chalky degrees were lowest in D2（5.40%）and D1 treatments（5.07%）for early rice and late rice,respectively.The amylose content of early rice decreased and then increased with density increased,and D2 treatment（15.73%）was the lowest,and that of late rice increased with density and then declined,D1 was lowest（15.97%）.The interaction effect of season and density significantly affected the percentage of polished rice（P<0.01）,chalkiness（P<0.01）and amylose content（P<0.05）of Yunda 107.In comprehensive,D2（21.00 million clusters/hm²,16.5 cm×40 cm）was the optimal planting density for Yunda 107 that could optimize the ears,number of grains per ear,seed setting rate and thousand-grain weight,etc.,could obtain higher grain yield and better rice quality with high rice pile survival rate,tiller number,panicle formation rate,SPAD（chlorophyll content）,stomata conductance,intercellular CO₂ concentration and dry matter accumulation.Therefore,the basic planting density of 210,000 plants per hectare with 16.5 cm plant spacing and 40 cm row spacing,is the best high-yield and high-quality cultivation techniques of Yunda 107 under twice harvests one year scheme.