The auxin transporter OsAUX1 regulates tillering in rice(Oryza sativa)

Tillering is an important agronomic trait of rice(Oryza sativa)that affects the number of effective panicles,thereby affecting yields.The phytohormone auxin plays a key role in tillering.Here we identified the high tillering and semi-dwarf 1(htsd1)mutant with auxin-deficiency root characteristics,such as shortened lateral roots,reduced lateral root density,and enlarged root angles.htsd1 showed reduced sensitivity to auxin,but the external application of indole-3-acetic acid(IAA)inhibited its tillering.We identified the mutated gene in htsd1 as AUXIN1(OsAUX1,LOC_Os01g63770),which encodes an auxin influx transporter.The promoter sequence of OsAUX1 contains many SQUAMOSA PROMOTER BINDING PROTEIN-LIKE(SPL)binding sites,and we demonstrated that SPL7 binds to the OsAUX1 promoter.TEOSINTE BRANCHED1(OsTB1),a key gene that negatively regulates tillering,was significantly downregulated in htsd1.Tillering was enhanced in the OsTB1 knockout mutant,and the external application of IAA inhibited tiller elongation in this mutant.Overexpressing OsTB1 restored the multi-tiller phenotype of htsd1.These results suggest that SPL7 directly binds to the OsAUX1 promoter and regulates tillering in rice by altering OsTB1 expression to modulate auxin signaling.

Relationship Between Heterosis and Parental Genetic Distance Based on Molecular Markers for Functional Genes Related to Yield Traits in Rice

The genetic distances among 18 cytoplasmic male sterile lines and 11 restorer lines were analyzed with molecular markers derived from yield-related functional genes. The correlation between parental genetic distance and heterosis was investigated by analyzing the performance of 47 combinations. The results showed that the genetic distance was significantly correlated with yield heterosis （r=0.29^＊）, but not significantly correlated with heterosis for other traits, such as number of effective panicles per plant, seed setting rate, 1000-grain weight, number of grains per panicle and theoretical yield. However, the correlation coefficient was so small that the parental genetic distance could not to be used to predict heterosis.

Exploration of rice yield potential: Decoding agronomic and physiological traits

Rice grain yield is determined by three major"visible"morphological traits:grain weight,grain number per panicle,and effective tiller number,which are affected by a series of"invisible"physiological factors including nutrient use efficiency and photosynthetic efficiency.In the past few decades,substantial progress has been made on elucidating the molecular mechanisms underlying grain yield formation,laying a solid foundation for improving rice yield by molecular breeding.This review outlines our current understanding of the three morphological yield-determining components and summarizes major progress in decoding physiological traits such as nutrient use efficiency and photosynthetic efficiency.It also discusses the integration of current knowledge about yield formation and crop improvement strategies including genome editing with conventional and molecular breeding.

Comparisons of yield performance and nitrogen response between hybrid and inbred rice under different ecological conditions in southern China

In order to understand the yield performance and nitrogen （N） response of hybrid rice under different ecological conditions in southern China, field experiments were conducted in Huaiji County of Guangdong Province, Binyang of Guangxi Zhuang Autonomous Region and Changsha City of Hunan Province, southern China in 2011 and 2012. Two hybrid （Liangyoupeijiu and Y-liangyou 1） and two inbred rice cultivars （Yuxiangyouzhan and Huanghuazhan） were grown under three N treatments （N1,225 kg ha-l; N2, 112.5-176 kg ha-l; N3, 0 kg ha-1） in each location. Results showed that grain yield was higher in Changsha than in Huaiji and Binyang for both hybrid and inbred cultivars. The higher grain yield in Changsha was attribut- ed to larger panicle size （spikelets per panicle） and higher biomass production. Consistently higher grain yield in hybrid than in inbred cultivars was observed in Changsha but not in Huaiji and Binyang. Higher grain weight and higher biomass production were responsible for the higher grain yield in hybrid than in inbred cultivars in Changsha. The better crop perfor- mance of rice （especially hybrid cultivars） in Changsha was associated with its temperature conditions and indigenous soil N. N2 had higher internal N use efficiency, recovery efficiency of applied N, agronomic N use efficiency, and partial factor productivity of applied N than N1 for both hybrid and inbred cultivars, while the difference in grain yield between N1 and N2 was relatively small. Our study suggests that whether hybrid rice can outyield inbred rice to some extent depends on the ecological conditions, and N use efficiency can be increased by using improved nitrogen management such as site-specific N management in both hybrid and inbred rice production.

Relationships of Panicle Type Index with Subspecies Characteristics and Yield Traits in Filial Generation of Crosses between Indica and Japonica Rice

Two recombinant inbred line （RIL） populations, one derived from a cross between Zhongyouzao 8 （indica） and Toyonishiki （japonica） and the other from a cross between Qishanzhan （indica） and Akihikari （japonica）, were grown in Liaoning and Sichuan Provinces, China, to study the panicle type index （PTI, the ratio of a number of node position on panicle axis where the secondary branch with the most numerous secondary branch grains is located to the number of primary branches） and its relationships with subspecies characteristics and yield traits. With continuous distribution of PTI and numerous of lines with different PTIs in the progenies, indica-japonica hybridization could be a method for breeding cultivars with ideal panicle type. PTI was significantly influenced by environments, with a significant decrease from Liaoning to Sichuan A significantly negative correlation was found between PTI and most of subspecies characteristics. PTI varied remarkably with different subspecies types. As a whole, it showed a trend of indica （H）〉indicalinous （H＇）〉japonicalinous （K＇）〉japonica （K） However, it is not appropriate to regard PTI as a parameter for subspecies classification in rice because it was recombined in the filial generations of cross between indica and japonica rice. The negative correlations were found between PTI and most of panicle characteristics, as well as yield-related traits. Based on PTI, most of lines from the two populations were middle dominant panicle type （the number of grains on the secondary branch is numerous in middle position of the panicle） and lower dominant panicle type （the number of grains on the secondary branch is numerous in lower position of the panicle and becomes less towards the top of panicle） with significant yield advantages.

Grain Yield and Nitrogen Use Efficiency of Hybrid Rice in Response to High Plant Density and Nitrogen Rate

Increased plant density with low N rate was a recommended strategy to increase grain yield and N use efficiency(NUE);however,grain yield,NUE and the total N uptake(TNU)responses of hybrid rice to this strategy at different yield levels(medium yielding site(MYS)Luzhou City and high yielding site(HYS)Deyang City had not been described.Field experiments with hybrid rice Rongyou1015 were conducted to study the effects of two plant densities.High plant density(HD),low plant density(LD)and four N rates(without N,N_(0);a recommended N rate of 195 kg•hm^(-2),N_(CK);a 23%reduction in N rate,N_(-23%);a 46%reduction in N rate,N_(-46%)on yield attributes,grain yield,TNU and NUE of hybrid rice were studied under different yield levels in 2016-2017.The results showed that the grain yield and NUE of hybrid rice in response to plant density and N rate varied with yield levels.For MYS,reducing N rate by 46%result in significantly lower grain yield at LD treatment;whereas at HD treatment the grain yield of hybrid rice under N_(-46%) and N_(CK) were equal.For HYS,reducing N rate by 46% result in significantly lower grain yield regardless of low plant density and high plant density;however,a reduction in N rate by 23%increased grain yield,AE_(N) by 36%,PFP_(N) by 31% and RE_(N) by 11% over N_(CK) at HD treatment.Higher grain yield of hybrid rice under the combination of HD with low N rate was attributable to improvement in spikelets per panicle and harvest index.The results suggested that high plant density with low N rate might be an effective approach to improve grain yield and NUE in rice production,but reduction in N application rate was determined,according to yield levels.

Yields and Nitrogen Use Efficiencies of Rice (Oryza sativa) at Different Sites Using Different Nitrogen Fertilizer Application Rates and Controlled-release Urea to Conventional Urea Ratios

Rice yields and nitrogen use efficiencies were studied at five sites in southwest China using two nitrogen fertilization rates and five controlled-release urea（ CRU） to ordinary urea（ U） ratios. The fertilizer treatments significantly increased rice yields compared with the control（ no nitrogen added） yields to different degrees at different sites. Applying CRU and U increased the rice yield more than adding the same amount of nitrogen as U only. Higher increasing production rate were found using a nitrogen application rate of 105 kg/hm2 than 150 kg/hm2. A 70∶ 30 CRU∶ U ratio increased the yield more than other four ratios. Nitrogen use efficiency was 21. 9% higher using a nitrogen application rate of 105 kg/hm^2 than 150 kg/hm^2,and 46. 6%,38. 1%,34. 7%,and 22. 2% higher than when only U was applied when CRU∶ U ratios of 70 ∶ 30,50 ∶ 50,100 ∶ 0,and 30 ∶ 70,respectively,were used. A 70 ∶ 30 CRU ∶ U ratio gave the highest economic output（ yuan/hm^2）. Applying both CRU and U gave an output 3 078. 87 yuan/hm^2 higher at a nitrogen application rate of 150 kg/hm^2 than at a nitrogen application rate of 105 kg/hm^2. Economic output was always higher using both CRU and U than using U only. The highest economic output was given using a 70∶ 30 CRU∶ U ratio.Increasing the amount of nitrogen added decreased the output efficiency（ per hm2） because CRU is expensive. Significant relationships were found between the yield increase rate and the proportion of CRU added（ regression equation y = 7. 429 x-185. 7,R^2= 0. 663） and between the total rainfall over the whole growth period and the proportion of CRU added（ y =-0. 087 1 x ＋ 112. 29,R^2= 0. 687 9）. These regression equations can be used to determine the appropriate proportion of CRU that should be added at a site,depending on the rainfall and target rice yield.

Developmental Genetics Analysis for Plant Height in indica Hybrid Rice Across Environments

The developmental genetics of plant height was analyzed from two groups of three-line indica hybrid rice at two environmental conditions based on the NCII design, using the additive-dominant developmental genetics models and the statistic methods. The results showed that the rice genotypes and environmental conditions could both affect plant height, and the effects of environment on plant height decreased gradually with plant development. Additive and dominant effects both governed the performance of plant height at all developmental stages. However, the degrees of effect varied among the rice genotypes. Moreover, the interaction between environments and genotypes also affected plant height. The genetic effects differed at most developmental stages. Furthermore, the expressJon of additive effect was more active than that of dominant effect. Conditional interaction effects with environment also influenced plant height during genetic development, especially at the eady stage. Mid-parent heterosis （HMP） increased gradually with the developmental stage of plant height, and maximized at the latest stage, whereas the heterosis over the better parent （HBP） showed small differences among the genotypes, and kept stable at the later stage, with positive numeric value. At most developmental stages, conditional HMP was positively significant, while conditional HBP was negatively significant. All above results suggest that HMP and HBP have some new expressions in all developmental periods and the levels and directions are quite different.

Phenotypic Characterization, Genetic Analysis and Gene-mapping for a Brittle Mutant in Rice

Plant mechanical strength is an important agronomic trait of rice. An ethyl methane sulfonate （EMS）-induced rice mutant, fragile plant 2 （fp2）, showed morphological changes and reduced mechanical strength. Genetic analysis indicated that the brittle of fp2 was controlled by a recessive gene. The fp2 gene was mapped on chromosome 10. Anatomical analyses showed that the fp2 mutation caused the reduction of cell length and cell wall thickness, increasing of cell width, and the alteration of cell wall structure as well as the vessel elements. The consequence was a global alteration in plant morphology. Chemical analyses indicated that the contents of cellulose and lignin decreased, and hemicelluloses and silicon increased in fp2. These results were different from the other mutants reported in rice. Thus, fp2 might affect the deposition and patterning of microflbrils, the biosynthesis and deposition of cell wall components, which influences the formation of primary and secondary cell walls, the thickness of cell walls, cell elongation and expansion, plant morphology and plant strength in rice.

Genetic Diversity Analysis of Balsam Pear(Momordica charantia L.) by ISSR Marker

[Objective] The aim was to explore the relationship between the classification and regional distribution of balsam pear. [Method] In the research, 30 varieties of balsam pear were analyzed by ISSR marker. [Result] The research showed that172 bands were amplified by 18 primers, in which, 132 bands were polymorphism and the polymorphic proportion was 76.7%. All of the samples can be divided into four categories by UPGMA analysis. [Conclusion] The results indicated that the classification of balsam pear is similar as varieties' regional distribution, which will be useful for genetic relationships analysis and parents selection in hybridization breeding.