| Enhancement of sink capacity with greater panicle is an important approach to improve yield potential in super rice breeding.However,heavy panicle rice varieties were vulnerable to unstable environments,and their low and unstable seed-setting restricted the use scope and yield potential.Global warming and improper application of nitrogen fertilizer were main problems.To verify the population growth characteristics,the stability in grain filling and seed-setting and explore use value and limitations of heavy panicle rice varieties,the experiment was conducted on Yangtze university farm.In 2013,one group of heavy panicle rice varieties,screening by former studies from 21 heavy panicle indica varieties,had different temperature sensitivity and were used in the staggered sowing trails in order to verified the response on different temperatures.During 2014-2015,BL006(heavy panicle rice variety with dominant primary branches),R-nongbai(heavy panicle rice variety with dominant secondary branches)and Huanghuazhan(medium panicle rice variety with high seed-setting)were used as materials to investigate the characteristics of population growth and source-sink-flow in the field condition.In the meantime,to investigate the seed-setting stability under different environmental conditions(high temperature and high nitrogen)through potted plant trails and field trails.The major results were as follows:1.Heavy panicle rice varieties had distinct dry matter accumulation superiority.Compared with control,BL006 had dry matter accumulation superiority in the whole growth period.Before full heading,it had higher leaf area index,leaf area duration,net assimilation rate and dry matter accumulation.However,after full heading,leaf senescence induced lower net assimilation rate and poor dry matter production capacity.R-nongbai had the similar dry matter accumulation to control.The superiority appeared during full heading and 20 days after full heading with an increase by 63.59%,and the superiority was related to higher grain-leaf ratio,longer effective leaf area duration and higher net assimilation rate after full heading.Compared to BL006,R-nongbai had a balanced dry matter accumulation during the whole growth period.Besides that,the two varieties had lower stem sheath dry matter transport rates and smaller spike dry weight to plant dry weight ratios,which were lower by 14.86% and 9.24% than the control,respectively.2.The grain filling processes of heavy panicle rice varieties were synchronous,and grain filling rate was higher and centralized.Compared with control,BL006 and R-nongbai had higher chlorophyll contents,and chlorophyll contents changedconsistently with grain filling process,which indicated that the sources were sufficient for grain filling.BL006 and R-nongbai had higher grain filling rate,shorter grain filling duration,synchronous grain filling and heavier grain weights by 13.19% and10.07%,respectively.Vascular bundle characters of panicle neck and branches of BL006 were better,and those of R-nongbai were better in some ways.Besides that,vascular bundle characters of primary branches were better than those of secondary branches,and the primary branches had higher grain filling rate and grain weights than those of secondary branches.Compared to R-nongbai,BL006 had higher grain filling rate,shorter grain filling duration,heavier grain weights and smaller difference among grain positions.3.Heavy panicle rice variety R-nongbai had higher self-adjustment capacity.Leaf-cutting treatment lowered grain filling rate,shortened grain filling duration,and reduced spikelet fertility and thousand grain weight.For above indicators,the decrease degrees of primary branches on the upper position were smallest,those of the secondary branches on the upper position were largest for grain filling rate and thousand grain weight,and those of the secondary branches on the lower position were largest for spikelet fertility.The decrease degrees of BL006 and control were similar,but higher than those of R-nongbai.4.Heavy panicle rice varieties were vulnerable to variable environments,but,there were differences among varieties and positions.Results of temperature control experiment showed that,BL006 and R-nongbai were heat-intolerant,and Huanghuazhan was heat-tolerant.High temperature reduced spikelet fertility of BL006 and R-nongbai.Thousand grain weights of BL006 and R-nongbai were reduced under 30? treatment,but,their responses to 33? treatment were different for thousand grain weight.Under 30? treatment,the decrease degrees of secondary branches on the lower position for spikelet fertility and thousand grain weight were largest.But,Under 33? treatment,the decrease degrees of different positions for spikelet fertility were similar,and primary branches had higher decrease degree for thousand grain weights than secondary branches.In the other hand,under the field condition,spikelet fertilities were increased by 22.19% under heat treatment,and the increase extent of the lower positioned spikelets was highest.Generally,grain weight was decreased under heat treatment,but there were two opposite responses to heat treatment.Among them,grain weights of some varieties increased,and the increase extents of the middle and lower positions were higher than those of the upper position.Head milled rice rates were significantly decreased,chalky grain rates and chalkinessdegrees were significantly increased under heat treatment,and the influences were not significant for some rice varieties.The influences of heat treatment on rice qualities of each positioned grains were significant,and the influence extends in head milled rice rate and chalkiness degree for the upper positioned grains were higher than those for the other positions,but the influence extents in chalky grain weight for each positioned grains were similar.BL006 was more sensitive to nitrogen fertilizer,and Huanghuazhan was not sensitive to nitrogen fertilizer.For BL006,normal nitrogen condition was benefit for spikelet fertilization,and high nitrogen treatment was suitable for grain filling.For R-nongbai,high nitrogen treatment was suitable for fertilization and grain filling.High nitrogen treatment reduced spikelet fertilities and increased thousand grain weights of primary branches,however,high nitrogen did not influenced significantly spikelet fertilities and grain weights of secondary branches.In conclusion,heavy panicle rice varieties had distinct dry matter accumulation superiority,grain filling processes were obvious synchronous between superior and inferior grains,grain filling rates were high and grain filling durations were short.In general,BL006 was vulnerable to high temperature and high nitrogen,and R-nongbai was heat-intolerant but high nitrogen-dependent.BL006 had obvious dry matter accumulation superiority before full heading,however,grain-leaf ratio was little and leaf senescence was serious after full heading.R-nongbai had good“source-sink-flow” coordination,longer effective leaf area duration and obvious dry matter accumulation superiority after full heading and Spikelet fertilities and thousand grain weights of some heavy panicle rice varieties were increased by high temperature,rice qualities were generally deteriorated,but those of some varieties were not significantly influenced.Besides that,the grain-filling and seed-set under variable environments were related with grain position,tolerance and capability of adjusting photosynthesis level of each variety.Above results provide us a real possibility,that is,it is expected to overcome these bottleneck problems,unstable to environment,low and unstable seed-setting among years,in plain region,through further exploring the excellent properties and gene of heavy panicle rice varieties. |
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