Physiological And Genetic Mechanisms For Change Of Tiller Angle During Growth In Rice (Oryza Sativa L.)

Tiller belongs to a special kind of branch in cereal crops,an important trait related closelyto grain yield.The stature of tillers and their leaves has been intensively studied as a key issuein the field of tiller trait,and tiller angle determines the stature of tillers and their leaves onthem,which in turn affect light utilization and competition among plant individuals.Semi-scattered tiller growth could be favorable for rapid formation of leaf area for lightinterception,enhancing formation of complete canopy and improving competitiveness of plantsagainst weeds during vegetative growth.On the other hand,erect tillers at reproductive stagecould improve aeration and light penetration within a canopy,thus enhancing anti-biotic stressability and lodge resistance of rice plants.In the previous research,we obtained a rice genotypeDI508,which is characterized by semi-scattered tillers at vegetative stage and erect tillers afterbooting,i.e.showing dynamic change of tiller angle with the growth.It was also found that thetrait of dynamic tiller angle was related to their responses to photoperiod.In this paper,wecompared DI508 with erect genotype(Xieyou 9308 or 9308) and semi-scattered genotype(M09 or DI444) in morphological and growth characters,light and nutrient utilization.Thephysiological and genetic mechanisms for the tiller angle change was also were studied usingthe experiments involving sowing date and controlled temperature and photoperiod.Moreover,the QTL analysis of tiller angle change was conducted using a RIL population developed froma cross of Zhenshan97B and Miyang46 and RIL population developed from a cross ofXieqingzaoB and Miyang46.The main results are as follows:1.DI508 is typically characterized by fast growth at tillering stage,and erect shoots andvigor leaves in terms of photosynthesis after booting.At initial tillering stage,the angles of thefirst,second and third on the main shoots of DI508 were 59.74°,62.94°and 68.54°respectively,very similar to those of M09.After booting the angle was close to 90°,very similar to those oferect type rice 9308.The percentage of effective tillers developing into panicles in DI508 was68.35%,being 3.09% higher than that in M09.Dry biomass per plant of DI508 was 155.54 g atmaturity stage,being 15.84% and 64.09% higher than that of M09 and 9308,respectively,anddry biomass per tiller of DI508 was 9.15g,being 63.69% and 44.78% higher than that of M09and 9308 respectively.After booting until maturity,photosynthetic capacity of the most top 3leaves in DI508 kept stable and higher,being 26.89,25.69 and 24.83μmol.m^-2.s^-1 for 1th,2nd and 3rd leaves,respectively.In comparison,other two rice genotypes had lower photosyntheticrates.2.DI508 showed a better adaptability to light intensity in comparison with that of theother two rice genotypes.During tillering and milking stages,the maximum net photosyntheticrate and light saturation point of DI508 were the medium of Xieyou9308(erect tiller angle) andDI444(semi-scattered tiller angle).DI508 had obviously higher photosynthetic rate andapparent quantum yield,and lower light compensation point under weak light conditionrelative to those of the other two rice genotypes,Under all light intensities,carboxylationefficiency in DI508 were similar to that of the other two genotypes.However,at milking stage,DI508 had a higher value in carboxylation efficiency than DI444.In addition,DI508 hadhigher water use efficiency than the other two rice genotypes.3.The tiller angle of DI508 showed the dynamic change during its growth under all Nlevels,and its convergent index increased gradually after maximum tillering.However,thetiller angle and convergent index of DI508 was significantly affected by N level.Thus,tillerangle and convergent index were obviously greater in the treatment of 200 kg/ha or 400 kg/hathan that in the treatment 0 or 100 kg/ha.Similarly,tiller angle of DI508 showed the dynamicchange during the growth under different ratios of N,P and K application rates.Tiller angleand convergent index of DI508 were significantly affected by ratios of the three fertilizers,decreasing with increased ratios of P and K application.DI508 had higher N utilizationefficiency in terms of morphological traits and grain yield,as reflected by improved plant andcanopy height,tillers per plant,effective tiller percentage,net photosynthetic rate,specific leafweight,leaf area per plant,leaf area index,dry matter and yield with increased N fertilizer andratios of P and K fertilizer.4.DI508 plants gradually changed into erect when photoperiod became shorter(10-15 dafter 21^st June,the Summer Solstice),irrespective of seeding dates(4^th April,5^th May and 4^thJune) in a natural field.Under the controlled photoperiod,the tiller angle of DI508 plantschanged in the same way as happened in the field.Shorter lighting treatment(10 hours)advanced the angle changing while longer lighting treatment(14 hours) delayed the changing.The results showed that the critical photoperiod for tiller angle changing of DI508 is about 10hour.On the other hand,the tiller angle changing of DI508 was not affected by accumulated temperature or growing degree day(GDD).5.QTL analysis was conducted using a RIL population developed from a cross ofZhenshan97B and Miyang46 and RIL population developed from a cross of XieqingzaoB andMiyang46.At initial tillering,the QTLs for tiller angle of main shoots were detected inchromosomes 1 and 9 in both RIL and RIL populations.While at full-heading,the detectedQTLs for tiller angle were located on more chromosomes.The conditional QTLs for tillerangle from initial tillering to full-heading were detected in the both genetic populations usingconditional variable analysis and composite interval mapping.The conditional QTLs detectedin the genetic population of Zhenshan97B/Miyang46 were mainly located in chromosome 5and 9,and the conditional QTLs detected in the genetic population of XieqingzaoB/Miyang46were located in chromosome 6,8,9 and 11.