Effects of genes increasing the number of spikelets per panicle,TAW1 and APO1, on yield and yield-related traits in rice

The genes TAWAWA1 (TAW1) and ABERRANT PANICLE ORGANIZATION1 (APO1) increase the number of spikelets per panicle (SN). In the present study, we examined the effects of these genes on morphological traits, yield, and yield-related traits including yield components using the near-isogenic lines (NILs) in the genetic background of a japonica rice variety, Koshihikari – NIL-taw1, NIL-apo1-D3, and NIL-apo1-D4 – in a field experiment. The SN and total number of spikelets per area of the three NILs were larger than those of Koshihikari. However, the yield of the three NILs did not exceed that of Koshihikari due to their low filling ability. Interestingly, our field experiments indicated that TAW1 did not affect the diameter of internodes and the PN, whereas APO1 decreased the PN and increased the diameter of internodes. These results suggest that TAW1 and APO1 differently affect yield-related traits.     

Identification of quantitative trait loci for panicle structure and grain filling using a cross between indica- and japonica-type high-yielding rice cultivars

ABSTRACT

To enhance the yield potential of rice by breeding, it is important to reveal the genetic factors affecting yield components in high-yielding cultivars. Quantitative trait loci (QTL) analysis for panicle structure and spikelet weight as an index of grain filling was conducted using recombinant inbred lines (RILs) derived from a cross between an indica-dominant high-yielding cultivar, Takanari, and a japonica-dominant high-yielding cultivar, Momiroman in 2012 and 2013 in eastern Japan. The grain-filling ability of Takanari is reported to be better than that of Momiroman. Since grain filling is generally better near the tip of the panicle and decreases as the number of branches from the rachis increases, we classified whole panicles into upper and lower side panicles and spikelets into primary, secondary, and tertiary spikelets according to the number of branches from the rachis. On chromosomes 1, 4, and 6, QTLs regulating the number of spikelets per panicle and panicle structure were detected and were most likely identical to GN1a, SPIKE, and APO1, respectively, which has been previously reported as QTLs regulating the number of spikelets per panicle. Takanari produced much heavier secondary and tertiary spikelets than Momiroman on the lower side panicle. On chromosome 5, novel QTLs regulating spikelet weight were detected. The Takanari allele enhanced secondary and tertiary spikelet weight on the lower side panicle. These results indicate that it may be possible to enhance sink capacity and translocation of source with a combination of novel QTLs detected on chromosome 5 and GN1, APO1, and SPIKE.     

穴株数对水稻生长发育及产量的影响

本试验对2株/穴、3株/穴、4株/穴、5株/穴、6株/穴的生育进程进行跟踪调查,结果表明,每穴插秧株数以3～4株为宜,产量水平较高,经济效益较佳。     

Effect of heading date of perennial ryegrass cultivars on tillering and tiller development in spring and summer

Three cultivars (two diploid and one tetraploid) in each of three maturity groups (early, intermediate and late) of perennial ryegrass were sown in 10 m² plots, replicated four times, in Northern Ireland in June 1997 in a study of the effect of heading date on tiller development (including initiation to flower) and turnover of tillers produced at specific times in spring in 1998 and 1999. The plots were harvested seven times in each year. Annual dry‐matter production was similar for all groups in each year. In spring and early summer of both years, tiller density of the diploid cultivars was 1·5 times greater than that of the tetraploid cultivars and the mean tiller density over all swards in June was about 0·40 times greater than that in April. Maximum proportions of reproductive tillers in the early, intermediate and late maturity groups, determined from apical dissections, were found in early April, mid‐May and early June, respectively. Although a high proportion of tillers, which were present when annual observations commenced in spring, was decapitated at the first harvest in the early group, the previous population density was maintained by rapid production of new tillers during May, including those from suppressed tiller buds during reproduction. It is concluded that the relationship between heading date and rate of tiller turnover (including flowering) at specified times in spring is important in sward management throughout the early part of the growing season and should be taken into account in tiller‐based grass growth models.     

The difference in amylose content within a panicle as affected by the panicle morphology of rice cultivars

The variation of amylose content (AC) among grains within a panicle and its relation to panicle morphology were investigated using 44 japonica rice cultivars differing in grain density (GD), panicle bending degree (BD) and palatability. Morphological traits of the rice panicle were poorly associated with mean grain AC on the average of the whole panicle, but closely related to AC variation and spatial distribution within a panicle, with the compact-panicle cultivars (GD>6.5 grain/cm and BD< 30°) having greater variation than loose-panicle cultivars (GD<6.0 grain/cm and BD>70°). The extent of AC differences among the rachides within a panicle was also cultivar-dependent, and greater differences were found between middle and top rachides for the compact-panicle cultivars, and between middle and bottom rachides for the loose-panicle cultivars. The difference in spatial distribution of AC variation between Bing110 (a compact-panicle cultivar) and XS11 (a loose-panicle cultivar) indicated that grains with low AC were principally distributed on interior rachis of middle branches for Bing110, but on bottom-rachis for XS11. Such a distribution is basically associated with the difference in the timing procedure of floret initiation and development, and final grain weight.     

N applications that increase plant N during panicle development are highly effective in increasing spikelet number in rice

Efficient use of nitrogen fertilizer is critical in improving yield stability in rice. The objective of this study was to determine the effect of nitrogen (N) top-dressing on the number of total spikelet (fertile plus sterile) production and evaluate the effect among rice cultivars. We analyzed 136 sets of experimental data on growth and spikelet production for three lowland cultivars, grown under various regimes of N over 10 seasons at Kyoto, Ibaraki and Kanagawa, Japan. In each season, one to three of the lowland cultivars, Nipponbare (japonica), Koshihikari (japonica) and Takanari (indica), were studied. In 1986, 1995 and 1999-2001, the N regimes included basal application only, light basal and heavy top-dressing from the panicle initiation stage onward, heavy basal and heavy top-dressing from the spikelet formation stage onward, and no applications. In 2002 and 2005-2008, we set up experimental plots with varied time of N top-dressing, with or without N basal application. Takanari had the largest spikelet number averaged over all plots and was considered better efficient in spikelet production per applied N than the other cultivars. Although the trend is not clear, the effect of time of top-dressing on spikelet number was generally the greatest when N was top-dressed from 35 to 30 days before heading. The variation of observed spikelet number was analyzed with a linear regression of plant N 14 days before heading and by a model that estimates spikelet production accounting for plant N 14 days before heading and crop growth rate (CGR) during the 14-day period preceding heading. For the variation of spikelet number within each cultivar, the linear function model expressed the observed spikelet number than the two function model with R² 0.43** versus 0.13*-0.28** for the former and later models, respectively. When the results of all cultivars were combined, the two function model was much better for estimation of spikelet number than the linear function model (R² = 0.36** vs. 0.20*). This indicates that yearly and varietal variation of spikelet number was caused mainly by plant N status at the late spikelet differentiation stage. The varietal variation in spikelet production efficiency is explained by CGR during this 14-day period. We concluded that N applications that increase plant N 14 days before heading is highly effective in maximizing spikelet production among cultivars.     

Low temperature-induced sterility in rice: Evidence for the effects of temperature before panicle initiation

Spikelet sterility of rice (Oryza sativa L.) results from low temperatures during panicle development. However, this temperature alone cannot fully explain the fluctuations in sterility observed in the field, since the susceptibility of rice plants to low temperature often changes according to its physiological status during sensitive stages. In the present study, we examined whether temperatures before the panicle initiation stage (PI) influence the plant's susceptibility to sterility during panicle development. To test this, we conducted a 2-year pot study and an analysis of field data using a model of cooling degree-days (CDD). In the pot study, the air temperature (T_a) and water temperature (T_w) were controlled independently for 3 weeks during the vegetative growth stage before PI. After PI, the plants were submerged in a cool water bath at a critical temperature of 19.5 °C to induce floral sterility. We found that low T_w during vegetative growth significantly increased the sterility. Low T_a during vegetative growth also significantly increased the sterility, but this effect was diminished by warm T_w even at low T_a. There was a close and negative correlation between sterility and T_w during vegetative growth. In the analysis of field data, we introduced CDD using temperatures below a threshold level of 20 °C to represent the magnitude of the exposure to low temperature from PI to the heading stage. Data of T_a was used for this analysis because data of T_w was scare. The CDD model was applied to 77 independent data sets collected at nine Agricultural Research Centers during four typical cool summers (1980, 1988, 1993, and 2003) in northern Japan. Year-to-year variations in sterility at one site were roughly accounted for by the variations in CDD, but large deviations were observed among the years. The deviations were related to T_a averaged over the 30-day period before PI. For a similar level of CDD, the lower the T_a before PI, the greater the sterility. Similar deviations were observed in the between-site relationships between sterility and CDD, and these deviations were related with the T_a before PI. These results suggest that temperatures before PI, and especially T_w, change the susceptibility of a rice plant to low temperatures during panicle development.     

Effects of the number of pollen grains on cold tolerance at the booting stage in rice lines with QTLs for cold tolerance

This study was conducted to clarify the relationship between the number of pollen grains per anther and spikelet fertility under low temperature conditions in the rice cultivars and lines including lines with quantitative trait loci (QTL) for cold tolerance, adapted to the Tohoku region of northern Japan. Cold-water treatment decreased anther length, the number of pollen grains per anther, and spikelet fertility in all cultivars and lines. The number of pollen grains was proportional to anther length in all cultivars and lines and under all temperatures. Spikelet fertility decreased with decreasing the number of pollen grains in cold-water treatments at 18.5 and 19.3?°C. ‘Ouu 415’, with the qLTB3 QTL for cold tolerance, had 28% more pollen grains and 9% higher spikelet fertility than the recurrent parent, ‘Hitomebore’, in the 18.5?°C cold-water treatment, suggesting that qLTB3 increased both parameters. Lines with the qCTB8 QTL for cold tolerance had significantly more pollen grains in two of the three years and significantly higher spikelet fertility in all three years in the 19.3?°C cold-water treatment, suggesting that qCTB8 reinforced cold tolerance. Ctb1, a proposed cold-tolerance QTL, had no effect on the number of pollen grains or spikelet fertility. In conclusion, the cultivars and lines with more pollen grains had a higher cold tolerance. Some of QTLs were inferred to increase the number of pollen grains and reinforce cold tolerance.     

Positional variations in phytic acid and protein content within a panicle of japonica rice

Six japonica rice cultivars differing in phytic acid and protein content were used to investigate the effect of grain position in the panicle on grain weight, phytic acid and protein content. There were significant differences in grain weight, albumin, globulin, prolamin, glutelin, and total protein content among the grains within a panicle for all six cultivars, but no differences were found for phytic acid content. An effect of grain position between primary rachises on grain weight and protein content was clearly detected, while that among top, middle and bottom rachis showed a greater change, varying with the cultivar. Albumin and globulin contents tended to be lower in the grains on the primary rachis than in those on the secondary rachis, and glutelin and total protein contents showed the opposite trend in the three cultivars with lower protein content. There was no significant correlation between phytic acid and protein content in the different grain positions within a panicle. The accumulation of phytic acid and protein during grain development appears to be independent.     

Identification of CMS maintainers and restorers for hybrid rice development in Ghana

The cytoplasmic-genetic male sterility is the most widely used system for hybrid rice (Oryza sativa) seed production. It requires three lines: the two hybrid parents (A and R lines) and a third line (maintainer (B line)), which maintains the sterility of the female parent during seed increase. Studies were undertaken to identify maintainers and restorers for introduced cytoplasmic male sterile (CMS) lines using simple sequence repeat (SSR) markers and testcrosses. Molecular screening with SSR marker RM6100 grouped the assembled inbred lines into 30 potential restorers and 55 potential maintainers. One maintainer (WAS 127 -12-1-6-3-1) and 16 restorers were confirmed by testcrosses. WAS 127-12-1-2-3 had higher grain yield per plant in crosses with CMS1 (IR69625A) than the local checks (AgraRice and Jasmine 85) and could be used as a restorer to develop a locally adapted, high-yielding hybrid. Conversion of WAS 127 -12-1-6-3-1 into a local CMS line was stopped because of sterility instability in the BC₁F₁ generation. Continued testcrosses to the set of identified potential maintainers could help identify a stable one that can successfully be converted into a locally adapted CMS line.     

栽培因素对北方粳稻产量及米质的影响(Ⅳ)--插秧株数对产量及米质的影响

2002～2003年开展插秧株数对北方粳稻产量及米质影响试验,结果表明,在30 cm×20 cm密度条件下,1穴内每增加1株苗,株高降低1.5 cm;叶片减少0.3个;有效分蘖略有增加.每穴插2～3株苗时产量最高,1、4株次之,5株最低.穴插3株苗左右时加工品质最好,外观品质是随插秧株数的增加而变劣.除插1株时稻米中蛋白质含量有所增加外,其他处理的直链淀粉和蛋白质含量没有多大区别.     

不同基本苗对早稻分蘖和产量形成的影响

以两系杂交早稻陵两优211与常规早稻品种湘早籼6号为材料,比较不同基本苗数对早稻农艺性状及产量构成因素的差异。结果表明:(1)基本苗6~8苗/穴时,每穴茎蘖数明显多于1~4苗/穴处理,且能更早达到分蘖高峰。(2)分蘖期叶面积指数与基本苗数呈正相关,而在乳熟期叶面积指数、叶片SPAD值与基本苗数均呈负相关。(3)成熟期地下部分和地上部分干物质量随基本苗数增加表现为先增加后降低的趋势,地上部分干物质量均以移栽苗数4苗/穴最高,杂交早稻地下部分干物质量以移栽苗数4苗/穴最高。(4)产量随基本苗数增加而增加,有效穗数变化趋势与产量一致,每穗总粒数、实粒数和结实率与产量变化趋势相反,但每穗实粒数、结实率和千粒重各移栽苗数处理间差异不明显,受品种遗传特性的影响可能较大。(5)随着移栽苗数的增加,杂交早稻产量的最大增长幅度没有常规早稻的大,有效穗数也呈现相同趋势。试验结果表明每穴插3~5苗是获得早稻高产稳产的重要措施。     

水的垂直渗透对水稻生长发育的影响研究

通过研究水的垂直渗透对水稻返青、水稻分蘖、水稻产量的影响,提出通过完善排水工程、设施,定期深耕田地,改善土壤渗透性,为水稻高产奠定基础.     

水的垂直渗透对水稻生长发育的影响研究

通过研究水的垂直渗透对水稻返青、水稻分蘖、水稻产量的影响,提出通过完善排水工程、设施,定期深耕田地,改善土壤渗透性,为水稻高产奠定基础。     

Effects of salt and low light intensity during the vegetative stage on susceptibility of rice to male sterility induced by chilling stress during the reproductive stage

We tested whether exposing rice plants to abiotic stress (salt or shade) during vegetative growth affects the chilling tolerance of reproductive organs, which is one of the most important traits for rice growing in a cool climate; we used two rice cultivars with different tolerance in two growing seasons. We divided the vegetative growth into three phases to clarify the most sensitive period: 7–22 days after transplanting (DAT), 23–38 DAT and 39–54 DAT. Chilling tolerance of the pre-stressed plants was based on the male sterility induced by low temperatures. Shade and salt stress during all three vegetative growth phases significantly reduced stomatal conductance. Shade decreased the specific leaf weight and the leaf sugar and starch contents, but salt had no significant effect, despite causing leaf damage. Low temperatures during the reproductive stage induced spikelet sterility in all plants, but the magnitude was greater in the salt- and shade-stressed plants of both cultivars, especially those stressed late during vegetative growth. The increased spikelet sterility caused by chilling was closely related to the reduction of the total spikelet number per panicle. This is the first study to show that salt and low light stress during vegetative growth increased the susceptibility of rice plants to chilling damage during panicle development.     

寒地水稻稻瘟病和褐变穗综合防治效果研究

为更有效的防治水稻稻瘟病和褐变穗,特进行此试验,结果表明,防治效果最好的药剂为2%加收米液+3.5%多抗霉素+25%咪鲜胺,并通过降低此类病害的发病率达到增产的目的,采用2%加收米液+3.5%多抗霉素+25%咪鲜胺的处理实际产量为658.9 kg/667 m~2,较空白对照增产10%。     

水稻株型特征与产量构成关系的研究

选用4个不同株型水稻品种,研究了株型指标、产量构成以及两者之间的关系。结果表明不同株型品种叶片角度与枝梗数存在一定的相关性,其中:沈农606剑叶基角和剑叶开张角与一次枝梗数呈负相关;辽粳294倒二叶基角与二次枝梗数呈负相关;秋光穗基角与二次枝梗数呈负相关;辽盐16倒二叶基角与一次枝梗数、千粒重呈负相关。在株高相差不大的情况下,茎秆粗壮是沈农606抗倒伏的主要原因。紧凑型品种各叶位叶绿素含量较高,而且不同叶位叶绿素含量差异较小。紧凑型品种的株型有利于产量的形成;对披散型品种进行株型改良有利于其形成更好的群体。     

Rapid prediction of head rice yield and grain shape for genome-wide association study in indica rice

Rice milling and appearance qualities are the main determinants of market price of the milled rice, so great breeding efforts have been directed to improve the milling and appearance quality. The success of breeding efforts depends on the accurate and rapid phenotyping of the quality traits in early generations. This study was conducted to first validate the effectiveness of the PaddyCheck to measure head rice yield (HRY) and paddy grain length of 40 indica rice cultivars. The results indicated that the PaddyCheck data had positively correlated with the lab methods of HRY (r = 0.81**) and grain length (r = 0.97**). An association panel including 281 indica rice accessions was phenotyped with the PaddyCheck and the data were used for genome-wide association study (GWAS) to identify quantitative trait locus (QTL) for milling and appearance quality. A total of nine QTLs were identified, among which the major genes GS3 and qSW5 were identified for grain length and width, respectively. Furthermore, a novel QTL on short arm of chromosome 6 was identified for HRY. Our study indicated that PaddyCheck measurement was accurate and effective, and could be applied in rice breeding for improvement of grain shape and milling quality. The nine QTLs identified in indica rice could be used in marker assisted selection in rice breeding programs.