The number of spikelets per panicle in rice is determined by characters of the panicle such as the number of primary branches (PB) and secondary branches (SB) and panicle length (PL). It is a quantitative traits controlled by several genes. In this study, the nucleotide polymorphism and haplotype diversity of coding region of genes related to number of spikelets per panicle (SPP), including APO1, APO2, FON1, DEP1, GN1a, GHD8, HD1, and SP1, were analyzed using 45 varieties which showed significant phenotypic variations for PL, PB, SB and SPP. Significant correlations were observed among all the panicle traits. A total of 151 polymorphisms, including 114 SNPs and 26 indels were detected in coding region of 8 genes which constructed 52 haplotypes. Neutrality tests revealed that population subdivision event or balancing selection occurred in locus of APO2, FON1, and HD1 whereas no significant deviation from neutrality was detected in the other genes, suggesting a neutral evolution. Based on the results of GLM association analysis, 34 polymorphic sites in 6 genes were significantly related with the 4 panicle related-traits.

The spikelet number per panicle (SPP) in rice is a quantitative trait controlled by numerous genes. To identify the alleles of these genes, we conducted sequencing of coding region or UTR of 13 genes which are known for controlling SPP trait, subjected to 48 rice cultivars covering 27 Indica, 17Japonica, and 4 Tongil types. The genes were EP3(ERECT PANICLE 3), RCN1(REDUCED CULM NUMBER 1), RCN2(REDUCED CULM NUMBER 2), FZP(FRIZZY PANICLE), LAX1(LAX PANICLE 1), MOC1(MONOCULM 1) APO1(ABERRANT PANICLE ORGANIZATION 1), APO2(ABERRANT PANICLE ORGANIZATION 2), DEP1(DENSE AND ERECT PANICLE 1), FON1(FLORAL ORGAN NUMBER 1), GHD8(GRAIN NUMBER, PLANT HEIGHT, AND HEADING DATE 8), GN1A(GRAIN NUMBER 1A), and HD1(HEADING DATE1). As a result, 1 synonymous SNP was found in EP3, RCN1 and RCN2. In LAX1 and MOC1, 1 non-synonymous SNP was identified. But none of SNP was found from the coding region of FZP. Moreover, 3, 6, 7, 8, 9 and 10 alleles were detected in APO1 and APO2, FON1, GHD8, GN1A, DEP1, and HD1 respectively. The multiple regression analysis revealed that GHD8, DEP1 and HD1 had strong effects on spikelet number of primary branch. In addition, HD1 had strong effects on spikelet number of secondary branch, and for total spikelet number per panicle as well. This work was supported by a grant from the Next-Generation BioGreen 21 Program (Plant Molecular Breeding Center No. PJ008125), Rural Development Administration, Republic of Korea.

Spikelets per panicle (SPP) is one of the most important traits associated with rice yield. In this study, IL28, a near isogenic line (NIL) developed by introgressing chromosomal segments from ‘Moroberekan’ into ‘Ilpumbyeo’ showed significantly higher number of spikelets per panicle than the recurrent parent, ‘Ilpumbyeo’. Quantitative trait locus (QTL) analysis in 243 F2 plants derived from a cross between IL28 and Ilpumbyeo indicated that a QTL for spikelets per panicle, qSPP6 was located in the interval RM3430 - RM20580. The Moroberekan allele increased SPP. The fact that QTLs for panicle length and the number of secondary branches were mapped in the same interval as qSPP6 appears to indicate that this locus was associated with panicle structure. To map the QTL more precisely, substitution mapping of qSPP6 using F3 lines was conducted. Substitution mapping with 41 F3 lines further narrowed the interval containing not only qSPP6 for spikelets per panicle but also qNDW6 for node width to about 680-kb between markers RM20521 and RM20572 based on Nipponbare genome sequence. The locus, qSPP6 is of particular interest because of its independence from undesirable height and flowering time. SSR markers tightly linked to the qSPP6 will facilitate cloning of the gene underlying this QTL as well as marker assisted selection for variation in SPP in the breeding program.

Spikelets per panicle is one of the most important trait associated with rice yield component. In this study, IL28, near isogenic line (NIL) developed by introgressing chromosomal segments from Moroberekan into Ilpumbyeo, showed significantly higher number of spikelets per panicle than the recurrent parent Ilpumbyeo. Quantitative trait locus (QTL) analysis in 243 F2 plants derived from a cross between IL28 and Ilpumbyeo, indicated that a QTL for spikelets per panicle, qspp6, located in the interval RM3430 – RM20580. The fact that QTLs for panicle length and secondary branch number were mapped in the same interval as that for qspp6 indicated that this locus was associated with panicle structure. To map the QTL more precisely, substitution mapping of qspp6 using F4 lines was conducted. As a result, substitution mapping with ten F4 lines further narrowed the interval containing qspp6 to about 429kb between marker RM20521 and RM20562 based on the japonica genome sequence. The locus, qspp6 is of particular interest because of its independence from undesirable height and flowering time. SSR markers tightly linked to the qspp6 will facilitate cloning of the gene underlying this QTL as well as marker assisted selection for variation in SPP in an applied breeding program.

Four different rice varieties, Sindongjinbyeo, Dongjin #1, Saegyehwabyeo, and Iksan 467, were transplanted under three different nitrogen levels and two different seedling numbers per hill to obtain basic information on panicle traits under different cultural conditions and to propose the ideal panicle structure in Japonica rice. Sindongjinbyeo and Iksan 467 were characterized by more primary rachis branches (PRBs) per panicle and more grains on PRB than other cultivars. The two varieties also had fewer secondary rachis branches (SRBs) per PRB and fewer grains on SRB per PRB. These characteristics, consequently, resulted in higher ripened grain rate, contrary to that of Dongjin #1 and Saegyehwabyeo. In the correlation coefficient analysis, PRB number per panicle and grain number on PRB per panicle were positively correlated with ripened grain rate, while SRB number per panicle, number of grains on SRB per panicle, SRB number per PRB, number of grains on SRB per PRB and grain number per panicle were negatively correlated with ripened grain rate. Therefore, the number of grains on PRB per panicle, SRB number per PRB and the number of grains on SRB per PRB were the appropriate criteria for determining and achieving higher ripened grain rate in rice. High ripened grain rate over 90% was obtainable with over 12.5 PRBs per panicle and 63 grains on PRB per panicle, and with under 1.7 SRBs per PRB, 5 grains on SRB per PRB, 130 grains per panicle, and 14 panicles per hill. The study recommended that for over 90% high ripened grain rate, the critical limiting factors should be under 2 SRBs per PRB, 6 grains per PRB, and 130 grains per panicle, irrespective of the PRB number per panicle and the number of grains on PRB.

Spikelet number per unit area(SPN) is a major determinant of rice yield. Nitrogen nutrition status and biomass during reproductive stage determine the SPN. To formulate a model for estimating SPN, the 93 field experiment data collected from widely different regions with different japonica varieties in Korea and Japan were analyzed for the upper boundary lines of SPN responses to nitrogen nutrition index(NNI), shoot dry weight and shoot nitrogen content at panicle initiation and heading stage. The boundary lines of SPN showed asymptotic responses to all the above parameters(X) and were well fitted to the exponential function of f(X)=alphacdot1- etacdotexp(gamma;cdot;X) . Excluding the constant, from the boundary line equation, the values of the equation range from 0 to 1 and represent the indices of parameters expressing the degree of influence on SPN. In addition to those indices, the index of shoot dry weight increase during reproductive stage was calculated by directly dividing the shoot dry weight increase by the maximum value (800 extrmg/m-2 ) of dry weight increase as it showed linear relationship with SPN. Four indices selected by forward stepwise regression at the stay level of 0.05 were those for NNI (INNIP ) at panicle initiation, NNI(INNIh ) and shoot dry weight(IDWh ) at heading stage, and dry weight increase(IDW ) between those two stages. The following model was obtained: SPN=48683ㆍ IDWH 0.482 ㆍ INNIp 0.387 ㆍ INNIH 0.318 ㆍ IDW 0.35 ). This model accounted for about 89% of the variation of spikelet number. In conclusion this model could be used for estimating the spikelet number of japonica rice with some confidence in widely different regions and thus, integrated into a rice growth model as a component model for spikelet number estimation.n.n.

일반계인 추청벼, 화성벼와 통일계인 남풍벼를 공시하여 질소시비량(6, 12, 18, 24, 30kg/10a), 분시방법(기비-분얼비-수비; 50-25-25%, 30-30-40%) 및 생식생장기의 차광처리 (유수분화 후 15일, 30일 및 출수전 30일간)가 단위면적당 영화수형성에 미치는 영향을 검토하였으며 결과를 요약하면 다음과 같다. 1. 단위면적당 수수는 질소시비량 24kg/10a까지 시비량의 증가에 따라 직선적으로 증가하였고 분시방법에 따른 차이는 없었다. 생식생장기의 차광처리에 의해 추청벼에서만 수수의 유의한 감소가 나타났는데, 생식생장기 30일간의 차광처리에서 수수의 감소가 가장 크게 나타났다. 2. 수당 1차지경수는 질소시비량 18kg/10a까지 시비량의 증가에 따라 다소 증가하는 경향이었으나 증가폭은 크지 않았으며, 분시방법에 따른 차이는 없었다. 단위면적당 1차지경수는 질소시비량 증가에 따라 증가하였는데 이는 수당 1차지경 증가보다는 단위면적당 수수의 증가가 주원인이었다. 차광에 따라서는 추청벼에서만 단위면적당 1차지경수의 유의한 감소가 있었으며, 이는 수당 1차지경수의 감소에 의한 것이 아니라 단위면적당 수수의 감소에 의한 것이었다. 3. 수당 2차지경 분화수는 질소 12-18kg/10a까지는 시비량의 증가에 따라 다소 증가하는 경향이었으나, 2차지경 퇴화수는 분화수가 많아짐에 따라 증가하여 수당 2차지경수는 질소 시비량에 따른 차이는 작았다 생식생장기의 차광처리에 의해 수당 2차지경분화수에는 차이가 없는 반면, 퇴화 2차지경수에는 큰 차이가 있었다. 단위면적당 2차지경수는 질소시비량이 18kg/10a까지 증가함에 따라 많아졌으나 분시방법에 따른 차이는 없었으며, 차광처리에 따라 유의하게 감소하였다. 4. 단위면적당 영화수는 18-24 kg/10a까지는 질소시비량 증가에 따라 증가하였으나 그 이상에서는 더 이상 증가하지 않았고, 분시방법간에는 차이가 없었다 생식생장기 차광에 의해 단위면적당 영화수가 감소되었는데, 유수분화기후 30일간의 차광처리에서 가장 컸고, 수잉기 15일 차광처리에서 감소정도가 가장 적었다. 5. 단위면적당 영화수의 변이에는 영화수 구성요소중 단위면적당 수수와 2차지경상의 영화수의 변이가 기여하는 정도가 가장 컸으며, 1차지경의 기여도가 가장 적었다.