Percentage Of Productive Tillers Research Articles

Improving grain yield and nitrogen use efficiency of direct-seeded rice with simplified and nitrogen-reduced practices under a double-cropping system in South China.

Enhancing grain yield and nitrogen use efficiency (NUE) of rice is of great importance for sustainable agricultural development. Little effort has been made to increase grain yield and NUE of direct-seeded rice under the double-cropping system in South China. Field trials were conducted during 2018-2020 with four treatments, including nitrogen-free, farmers' fertilization practice (FP), 'three controls' nutrient management (TC), and simplified and nitrogen-reduced practice (SNRP). Grain yield under SNRP averaged 6.46 t ha-1 during the three years and was 23.0% higher than that of FP but comparable to that of TC. Recovery efficiency (REN ), agronomic efficiency (AEN ), and partial factor productivity (PFPN ) of nitrogen under SNRP increased by 12.0-22.7%, 159.3-295.0% and 94.6-112.5% respectively compared with FP. Harvest index and sink capacity increased by 7.3-10.8% and 14.9-21.3% respectively. Percentage of productive tillers (PPT) and biomass after heading increased by 24.0% and 104.5% respectively. Leaf nitrogen concentration at heading and nitrogen accumulation after heading increased by 16.3% and 842.0% respectively. Grain yield was positively correlated with PPT, sink capacity, harvest index, biomass and nitrogen accumulation after heading, REN , AEN , and PFPN . Grain yield and NUE under SNRP were superior to those under FP and comparable to those under TC. Increase in sink capacity, higher PPT, more biomass and nitrogen accumulation after heading, and greater harvest index were responsible for high grain yield and NUE in SNRP with reduced nitrogen fertilizer and labor input. SNRP is a feasible approach for direct-seeded rice under a double-cropping system in South China. © 2023 Society of Chemical Industry.

Rice yield, water productivity, and nitrogen use efficiency responses to nitrogen management strategies under supplementary irrigation for rain-fed rice cultivation

Rainfall-adapted irrigation (RAI) or supplementary irrigation for rain-fed rice cultivation consumes less amount of irrigation water by harvesting rainfall and thus is vital for sustainable rice (Oryza sativa L.) production in multi-rain areas, including the Jianghan Plain in China. However, nitrogen management strategies influence rice growth and water and nitrogen utilization under RAI remains unclear. Thus, we conducted a two-year (2016 and 2017) field experiment at Jingzhou City, central China to investigate the effects of nitrogen management strategies on grain yield, crop water productivity (CWP), and nitrogen use efficiency (NUE) of rice under conventional flooding irrigation (CF) and RAI. The nitrogen management strategies included local farmers’ nitrogen fertilization (CN), common urea (30% nitrogen) blended with controlled-release nitrogen fertilizer (70% nitrogen) (U+CRF), and optimized nitrogen fertilization (ON), at a nitrogen rate of 180, 180, and 150 kg ha−1, respectively. Compared to the CF condition, RAI down-regulated the numbers of irrigation (−3 in 2016 and −4 in 2017) and reduced the total amount of irrigation water (−41.6% in 2016 and −45.6% in 2017), suggesting that rainfall-adapted irrigation enhanced the rainwater storage capacity and usage. RAI also increased root length, root and shoot biomass, net photosynthetic rate, crop growth rate, nitrogen accumulation, percentage of productive tillers, harvest index, and nitrogen harvest index. The U+CRF and ON increased or maintained these parameters compared with the CN. Compared to the traditional irrigation and nitrogen fertilization pattern (CF interacted with CN), RAI combined with U+CRF or ON enhanced root length and root biomass, and had a relatively high spikelets number per panicle, grains filled percentage, and 1000-grain weight, and thus produced a high grain yield. Moreover, the new treatment reduced amount of irrigation water and improved utilization of nitrogen fertilizer, resulting in a greater CWP and NUE. The enhanced grain yield, CWP, and NUE were associated with the increased root biomass and root length. Therefore, rainfall-adapted irrigation combined with the new nitrogen management (U+CRF or ON) can synergistically increase grain yield and resource use efficiency by improving root growth in rice.

Efforts to Improve Productivity of Paddy (Oryza sativa L.) Var. Inpari 30 by Settings of Planting and Different Cropping Patterns

Solar radiation is an essential factor in the process of plant metabolism. Indonesia has a rainy season and the dry season, which causes differences in solar radiation intensity. The purpose of this study was to obtain information on suitable planting times and optimal cropping patterns for rice in the dry season in an effort to increase plant productivity. The study was conducted using a nested design, with two factors. The first factor is planting time. The second factor is cropping pattern, a nested factor in planting time that consists of 3 levels of cropping pattern (CP). These experiments have six combinations, and these experiments were repeated three times. Cropping pattern of jajar legowo 40 cm x 20 cm x 12.5 cm can give the best results on the parameters of leaf area index, plant growth rate, percentage of productive tillers, weight per square meter and rice productivity. Rice productivity is greatly influenced by planting time and cropping patterns. The planting time in September produced the highest productivity, reaching 6.99 t ha -1 . While rice planted with jajar legowo cropping patterns (40 cm x 20 cm x 12.5 cm) had productivity up to 7.66 t ha -1 .

Growth Response And Results Of Local Upland Rice Cultivars West Sumatera On Ultisol Land

Upland rice whose cultivated on dry land, which has limited needs for growth and production. The low upland rice production is due to the lack of high yielding varieties that can adapt, especially to marginal lands such as Ultisol. There are quite many local upland rice lines, but their potential has not been tested much. This study aimed to obtain the growth and yield of local upland rice cultivars of West Sumatra on the best Ultisol soil. The study used a completely randomized design (CRD) with four replications. The treatments were four upland rice cultivars, which consisted of; Silayang (K1), Siarang (K2), Sirah (K3) and Sigudang (K4). This data observation was analyzed for variance, and if it had a significant effect, it was continued using DMRT at the 5% level. Observations were made on plant height, the maximum number of tillers, percentage of productive tillers, length of flag leaf, age of flowering, age of the first harvest, panicle length, number of grain per panicle, the weight of 1000 pithy grain seeds, and weight of pithy grain per clump. Based on the results of the study, it was concluded that upland rice cultivar Sirah had the best growth and yield on Ultisol soil. Based on the conclusion, it is recommended to use Sirah upland rice on Ultisol soil.

RESPONSE OF THE GROWTH AND YIELD OF CIHERANG RICE (Oryza sativa L.) AND WEEDS ON THE DIFFERENT PLANTING METHODS AND WEEDING FREQUENCIES

This study aimed to observe the growth and yield of Chiherang rice (Oryza sativa L) and weeds in response of different planting methods and weeding frequencies. We conducted the study in Semampir, Argorejo, Sedayu Sub-district, Bantul District on April until August, 2018. We arranged field study using randomized complete block design in 3x2 factorials with 3 times repetition. First factor was Jajar legowo (J) stratified as 3 levels; 2:1 (J1), 4:1 (J2), dan 6:1 (J3). Second factor was weeding frequency in 2 levels which were 2 times in 14 and 70 hst (P1) and 3 times in 14, 49 and 70 hst (P2). Observed variables include Ciherang rice growth (plant height, total tillers, percentage of productive tillers, fresh and dried weight of each plant), components of rice yield (grain dry weight of each harvest, percentage of filled grains, yield of each hectares), and weeds (type of weeds, fresh and dry weight of weeds). We analyzed results using variance analysis with significant level of 5%, followed with 5% DMRT test. We found that application of jajar legowo planting method and weeding frequency do not correlates with all growth and weeding frequency variables of Ciherang rice and weeds. 2:1, 4:1 and 6:1 jajar legowo planting methods do not show significant impact both on Ciherang rice growth and yield, and also weeds. Both 2 times (14 and 70 hst) and 3 times (14, 49 and 70 hst) also do not have significant impact on all variables observed.Keywords: Jajar Legowo, Weeding Frequency, Ciherang Rice

Effects of tridimensional uniform sowing on water consumption, nitrogen use, and yield in winter wheat

Wheat is a staple crop worldwide, but yields may diminish as climate change causes increasingly unpredictable patterns of precipitation and soil nutrient availability. Farmers are thus challenged to maximize planting efficiency to increase yield, while also improving their resource use efficiency. In this study the effectiveness of tridimensional uniform sowing was tested across a range of planting densities for winter wheat crops on the North China Plain. Tridimensional uniform sowing was tested against conventional drilling at three planting densities (180 × 104, 270 × 104, and 360 × 104 plants ha−1) and assessed for water consumption, biomass, nitrogen uptake and allocation, and aspects of yield. The tridimensional uniform sowing treatment outperformed the conventional drilling treatment in most metrics and at most planting densities, while performing markedly better at higher planting densities. Water consumption decreased and nitrogen efficiency increased. Tiller number and percentage of productive tillers, leaf area index, dry weight, and yield increased without a significant decline in grain protein. Nitrogen allocation was more efficient under tridimensional uniform sowing than with conventional drilling, and also varied according to annual precipitation and planting density. Both yield and grain protein contents were significantly correlated with the amount of pre-anthesis accumulated nitrogen translocated from vegetative organs to kernels after anthesis. Overall, a density of 270 × 104 plants ha−1 provided the highest water use efficiency and grain yield. Tridimensional uniform sowing will benefit farmers by forming stronger overall crops, promoting the coordinated improvement of yield, nitrogen uptake and efficiency, and increasing grain protein content at higher planting densities.

Progressive integrative crop managements increase grain yield, nitrogen use efficiency and irrigation water productivity in rice

It is a major challenge to achieve the goal of increasing grain yield, nitrogen use efficiency (NUE) and irrigation water productivity (IWP) in cereals. This study investigated if progressive integrative crop management technology in rice (Oryza sativa L.) could improve agronomic and physiological performances, and consequently, increase grain yield, NUE and IWP. A japonica rice cultivar and an indica-japonica hybrid rice cultivar were grown in the field, with five crop managements including an unfertilized 0N treatment (0N), local farmer’s practice (LFP), integrative crop management (ICM) 1–3 ((ICM1, ICM2, and ICM3)). The results showed that, when compared to LFP, the ICM could not only increase grain yield, NUE and IWP, but also improve agronomic and physiological performances. Both ICM1 and ICM2 increased economic benefit. The progressive effect on the yield, NUE, IWP, and agronomic and physiological performance was obvious with the progressive introduction of single cultivation technology. The ICM increased sink size (total number of spikelets), percentage of productive tillers, leaf area index and duration, crop growth rate, non-structural carbohydrate accumulation and remobilization, leaf photosynthetic rate, root dry weight and length, root oxidation activity, root bleeding, and zeatin and zeatin riboside content in roots and leaves. The results suggest that the integrative and optimized crop management could achieve the dual goal of increasing grain yield and resource use efficiency through improving agronomic and physiological performances, especially increases in sink size and shoot and root growth, leading to higher grain yield, NUE, and IWP.

Comparison and suitability of genotype by environment analysis methods for yield-related traits of pearl millet

Pearl millet (Pennisetum glaucum (L.) R. Br.) is an important food security and income crop for households living in semi-arid zones in Uganda. However, the genotype by environment interaction, in addition to the several methods used for its assessment, complicates selection of varieties adapted to such semi-arid areas. The objective of this study, therefore, was to compare common methods used to assess stability and adaptability of improved genotypes. Seventy six genotypes were planted in four environments in an alpha experimental design with two replications. Results showed that genotype by environment interactions were significant at p<0.05 for grain yield, days to 50% flowering and 50% physiological maturity, percentage of productive tillers and panicle area. Results further showed inconsistency in ranking of genotypes between methods; although Cultivar Superiority, REML, Yield Stability Index and GGE biplot were consistently correlated and identified high yielding and stable genotypes.Keywords: GGE biplot, grain yield, pearl millet, stability analysis, Uganda

Combining Ability and Heterosis for Grain Yield and Rust Resistance in Pearl Millet

<p> </p><p>Pearl millet is a dual-purpose crop in semi-arid zones of Uganda. However, no studies have been conducted to determine the gene effects for yield and yield-related traits and rust resistance in these environments; yet this knowledge is important in improving grain yield and rust resistance. A North Carolina II mating design was adopted to study the genetic effects for rust resistance and yield-related traits of improved pearl millet genotypes. The experimental design to study the objectives was alpha in two [locations, seasons and replications]. A higher proportion of general combining ability (GCA) effect was observed for grain yield, days to 50% flowering, days to 50% anthesis, flower-anthesis interval, days to 50% physiological maturity, plant height, total tiller number, number of productive tillers, percentage of productive tillers, panicle area, leaf area, 1000-grain weight, biological yield and harvest index. The specific combining ability (SCA) effect was predominant for area under disease progress curve. Eleven hybrids performed better than the best male parent and five crosses performed better than the best female parent for grain yield while all the fifteen selected best crosses performed better than all parents for area under disease progress curve. Ten crosses were more resistant to rust than the best male parent and all the crosses were more resistant to rust than the female parents. The additive gene action was predominant for grain yield, rust severity at 50% physiological maturity, days to 50% flowering, days to 50% anthesis, total tiller number, percentage of productive tillers, panicle area, 1000-grain weight, biological yield, harvest index and leaf area. High better-parent heterosis was also observed for most traits including grain yield and rust resistance. The traits were also characterized by relatively low levels of narrow sense heritability.</p>

Agronomic and Physiological Performance of Rice under Integrative Crop Management

Agronomic and physiological performances of a crop are closely associated with the yield and resource use efficiency. This study investigated if an integrative crop management (ICM) in rice (Oryza sativa L.) could improve agronomic and physiological performances and, consequently, increase grain yield, nitrogen use efficiency (NUE), and water use efficiency (WUE). A japonica hybrid rice cultivar was field‐grown in 2012 and 2013. Three treatments were conducted: no N application, local high‐yielding cultivation method (LHY), and ICM. The ICM consisted of the adoption of three practices: increased plant density, optimized N management, and an irrigation regime of alternate wetting and moderate soil drying. The ICM substantially increased sink size (total number of spikelets per m2), percentage of productive tillers, root oxidation activity, leaf area duration, non‐structural carbohydrate accumulation in the stem, and zeatin (Z) and zeatin riboside (ZR) content in roots and leaves. On average, the ICM increased grain yield by 18 to 19%, agronomic NUE (kg grain yield increase per kg N applied) by 67 to 70%, and WUE (grain yield per unit water consumed) by 27 to 28% over the LHY. The results suggest that the ICM could achieve the dual goals of increasing grain yield and resource use efficiency, and improved agronomic and physiological performances, especially increased sink size and enhanced root and shoot activities during the middle and late growth periods, contributed to high grain yield, NUE, and WUE in rice.

Effects of Different Cultivation Patterns on Population Quality of Japonica Hybrid Rice

A high quality of population is necessary to achieve high grain yield in rice, but little information is available on understanding how cultivation patterns affect population quality. In this study, two japonica hybrid rice cultivars Changyou 3 and Changyou 5 were grown in the field, with six cultivation patterns including no nitrogen application (0N), local high yielding cultivation (control), cultivation for high yielding and high efficiency (CHYHE), super high yielding cultivation (SHY), cultivation for super high yielding and high efficiency (SHYHE) and cultivation for high use efficiency of N (HUEN). The results showed that, the average yields of two cultivars under SHY and SHYHE were 12.0 t ha –1 and 10.9 t ha –1 , respectively, and 41.6% and 29.1% higher than these of control. Compared with the control, the SHY and SHYHE also significantly increased percentage of productive tillers, biomass from heading to mature, efficient and high efficient leaf area, grain-leaf ratio, leaf photosynthetic rate and SPAD values after anthesis , root-shoot ratio, and root bleeding after heading. The results indicated that the population quality of rice could be improved and higher yield could be achieved through integrating and optimizing cultivation techniques in rice production.

Population Quality of Rice under Different Irrigation Regimes

Establishment of a population with high quality is an important prerequisite to achieve high grain yield. Irrigation is one of the most important practices in rice production and plays a critical role in regulation of population quality. To understand the effect of irrigation regimes on population quality, we planted two rice cultivars currently used in the production, Yangdao 6 (an indica) and Yangjing 4038 (a japonica), treated with furrow irrigation between beds (FI), alternate wetting and soil drying (AWD), and traditional flooding as control (TF), for 10 days after transplanting to maturity. Compared with TF, FI and AWD increased grain yield by 10.60% and 8.43%, respectively. Both FI and AWD regimes reduced the number of unproductive tillers and increased percentage of productive tillers, area and length of the top three leaves, grain-leaf area ratio, light transmission rate, dry matter accumulation from heading to maturity, and increased photosynthetic rate of flag leaf, root activity and root biomass during grain filling. The results demonstrate that both FI and AWD could improve population quality, and consequently increase grain yield.

Effects of Deep-Flooding Irrigation on Growth, Canopy Structure and Panicle Weight Yield Under Different Planting Patterns in Rice

For rice cultivation in Japan, deep-flooding irrigation is used as a growth control method. To clarify the effects of deep-flooding cultivation under the different planting-pattern, we arranged conventional (Con, 22 hills m-2), narrow (Nar, 33 hills m-2) and very narrow (broadcast direct-seeding Model:BDSM, 100 hills m-2) planting plots under shallow-flooding (SF: 5 cm) and the deep-flooding (DF: 27 cm) conditions from active to maximum tillering stage and evaluated the growth, panicle weight yield, panicle components and community structure. DF was effective in controlling the weak tiller over the whole planting plots arranged. The panicle weight yield (m-2) was high in DF and high yield was kept even in BDSM. The panicle weight yield (m-2) increasesin DF was based on the panicle weight (panicle-1) increased by increasing secondary rachis-branches and their grains (Con and Nar), or on the panicle numbers (m-2) increase (BDSM). Shoot nitrogen content (tiller-1), reported to have the correlation with panicle components, was high in the Con and Nar in DF, and this might contribute to the increase in secondary rachis-branch grains. In BDSM in DF, the marked decrease in the percentage of productive tillers and serious lodging observed in SF were improved. The lodging resistance value in DF was higher than that in SF over the whole planting plots. The light transmission in DF was superior to that in SF in spite of the large LAI. Thus, the growth improving effect of DF was obvious over the wide planting pattern range.

Effects of Wheat Residue Application and Site-Specific Nitrogen Management on Growth and Development in Direct-Seeding Rice

The objective of this study was to investigate the growth and development of rice ( Oryza sativa L.) under the treatments of wheat ( Triticum aestivum L.) residue incorporation (RI) and nitrogen (N) fertilizer application. A mid-season japonica rice cultivar Yangjing 9538 was directly sown in field. Either in RI treatment or in the treatment with no residue return to field (R0), 3 nitrogen (N) fertilizer application levels were carried out, i.e., no N application, farmers' fertilizer practice (FFP), and site-specific N management (SSNM). The SSNM was based on chlorophyll meter readings in field. Compared with FFP, SSNM reduced N application by 30.0–31.3% and increased grain yield by 7.61% on an average. The average grain yield was 2.65% higher in the RI treatment than in the R0 treatment. Compared with the R0 or FFP treatment, the RI or SSNM treatment decreased stem and tiller numbers, leaf area index, and biomass accumulation at early growing period, but the differences were not significant after heading stage. RI was favorable for increasing the content of organic acid in leaves and enlarging the variations of temperature and relative humidity between day and night. The RI and SSNM treatments had positive effects on the percentage of productive tillers, photosynthetic rate of flag leaf, root activity, and ATPase activity during grain-filling stage.

Improvement of Lodging Resistance in Submerged Direct Seeding Rice (Oryza sativa L.) Cultivation Using a Newly Developed 'Shooting hill-seeder'. Effect of seedling density on the lodging resistance of hill-seeded rice as compared with that of broadcast-seeded rice.

打込み式代かき同時土中点播機を用いた安定的湛水直播栽培法の確立のため, 異なる苗立ち密度(40, 80および160本m-2)における耐倒伏性を散播水稲と比較して点播水稲の耐倒伏性に関する特性解明を行った. その結果, 点播水稲は散播水稲に比較して稈が長くなるために稈基部にかかる力が大きくなるが, 有効茎歩合が高いために耐倒伏性に関連した稈の形質が優れること, 押し倒し抵抗値が顕著に大きいことにより稲株の耐倒伏性が強化され, 倒伏を生じにくいことが明らかとなった. また, このような播種様式間差は苗立ち密度の高い条件で顕著となった. 押し倒し抵抗値の変動要因を検討した結果, 散播水稲において1株穂数が10本以下の株は押し倒し抵抗値の変動が大きく, 1株穂数の減少により抵抗値が顕著に低下するのに対し, 1株穂数が10本以上の株は押し倒し抵抗が安定して高かった. このことから, 散播水稲では苗立ち密度40本m-2以上の条件では1株穂数が10本以下となるために, 苗立ち密度の変動により1株穂数が変動するのに対し, 点播水稲は標準的な播種条件(条間30cm, 株間20cm)では苗立ち密度が40～160本m-2(1株苗本数が2～10本)の間で変動しても1株穂数が20～26本と安定して多いことにより, 苗立ち密度が変動しても点播水稲の耐倒伏性が安定して高いものと推察された. 湛水直播栽培では苗立ち密度の変動が避けられないため, このような特性を有する点播栽培は湛水直播栽培の安定化に有効であると考えられる.

Varietal differences in tillering ability of fourteen japonica and indica rice varieties

Field experiments were conducted to clarify the relation between the tillering ability and morphological characters, dry matter production, or nitrogen absorption among 14 rice varieties including different ecospecies with different plant types, and about the same heading time. Tiller number varied widely among the varieties and the number of tillers per plant at the maximum tiller number stage ranged between 14.3 and 39.5 in 1995 and 12.2 and 34.6 in 1996. Among all the varieties, IR 36 followed by Suweon 258 produced the highest maximum tiller number and Dawn produced the lowest maximum tiller number. The plant length and the specific leaf area, i.e. one of the indicators of leaf thickness, showed a strong negative and positive significant correlation, respectively, with the maximum tiller number. The varieties with a shorter plant length produced shorter and thinner leaves which would provide less competition for dry matter and nitrogen between mother stem and tillers and among tillers. This resulted in a higher efficiency of tiller production in the higher-tillering varieties for the same amount of dry matter production and nitrogen absorption. Percentage of productive tillers widely varied among the varieties, ranging from 42 to 73% in 1995 and from 50 to 81% in 1996. Semidwarf indica and japonica-indica varieties showed a lower percentage of productive tillers than the Japanese and tall indica varieties, and high-tillering varieties IR 36 and Suweon 258 produced the highest number of dead tillers, which resulted in the lowest percentage of productive tillers. The number of dead tillers depended mainly on the extent of competition for carbohydrates produced and nitrogen absorbed from the maximum tiller number stage to heading among tillers, although the increasing ratio of dead tillers was higher in indica varieties than in japonica varieties with a decrease in the amounts of these substances.

Interaction between N Application and Water Management in Dry-Seeded Rice

SummaryThe interaction between N application and water management (ordinary water (OW) and deep-water (DW)) in dry-seeded rice was studied in 1995 and 1996. Deep-water treatment increased the percentage of ripened grain and grain yield, and decreased panicle number per m2. The maximum number of tillers and the percentage of productive tillers was increased by increasing the amount of N applied (0, 70, 150, 220 kg ha–1) in both water treatments. More tillers was produced in OW than in DW. However, the percentage of productive tiller was higher in DW than in OW (78% in 1995 and 72% in 1996 for OW and 86% in 1995 and 83% in 1996 for DW). There were significant differences in yield components and yield between the amount of N applied, and between the two water treatments. The panicle number per m2 (r = 0.904** in OW, r = 0.921** in DW) was positively correlated with the amount of N applied. In DW, the number of panicles was lower than in OW, but the percentage of ripened grain was higher than in OW. The total nitrogen contents in the flag leaf was positively correlated with the amount of N applied and the concentrations of nitrogen in flag leaf was positively correlated with the grain yield. The partial factor productivity (PFP) of applied N was significantly higher in DW than in OW at all levels of nitrogen application. Agronomic nitrogen-use efficiency (ANUE) was not different between the two water treatments. These results imply that the suppression of tiller formation by elevated water level would improve the yield determinants and utilization efficiency of indigenous soil N, which consequently helps to increase yield production.

Studies on Agronomic Traits of African Rice (Oryza glaberrima Steud.): IV. Changes in growth, dry matter productivity and yielding ability related to domestication from wild to cultivated form

The changes in growth, dry matter productivity and yielding ability in the course of domestication from O. breviligulata to African rice (O. glaberrima) were examined. Between the two rice species, differences were hardly detected in plant height, culm length and final leaf number, although O. breviligulata had a wider variation of these characteristics as compared with African rice. The shorter strains tended to produce more tillers at the maximum tiller number stage, and the high tillering capacity was correlated with a low percentage of productive tillers, although the strains having a small number of grains per head showed a high percentage of productive tillers, in both species. No significant difference was detected between the two species in straw weight at maturity, and the differences in straw weight among strains were attributed to the differences in days required from transplanting to heading and to plant height. No significant difference between the two species was observed in top and total weights. The grain number per head was conversely related with panicle number in both species. Although the percentage of ripened grain tended to be slightly lower in O. breviligulata than in African rice, this may be attributed partly to the difference in grain number per hill. Single grain weight in O. breviligulata was nearly equal to that in African rice. These results suggest that agronomic traits such as growth, dry matter productivity and yielding ability have been changed only slightly in the course of domestication from O. breviligulata to African rice.

Analysis of Plant Characteristics Determining Ear Weight Increase during the Ripening Process in Rice (Oryza sativa L.) I. Plant characteristics determining the sink capacity of spikelets.

長稈型か短稈型かまた穂数型か穂重型かを表す示数としてそれぞれ稈長と1穂籾殻重を取り上げ, これらと最高分げつ期の茎数および有効茎歩合との関係を調査した. 最高分げつ期の茎数(X3)と稈長(X1)および1穂籾殻重(X2)との関係は次式によって近似することができた: X3=A-B・X1-C・X2(A, B, C; 係数). 有効茎歩合(y)とX2およびX3との間には次式の関係が認められた: y=α-(β+γlnX2) exP (δX3)(α, β, γ, δ係数). これら式から, 1) 1穂籾殻重の小さい品種では短稈化に伴って著しい穂数の増加が起こるが, ある程度大きな1穂籾殻重をもつ品種では必ずしも短稈化は穂数の増加に結びつかない, 2) 1穂籾殻重の小さい品種では短稈化が穎花容量(m2当たり籾殻重)の増大をもたらす, 3) 1穂籾殻重の増大に伴って穎花容量を最大にする最適稈長は大きくなる傾向にあるが, 1穂籾殻重がある程度以上大きくなると再び短稈化が穎花容量の増大をもたらす, ことが推定された. 韓国の「統一」系品種群にみられる大きな穎花容量は短稈化と大穂化が並行して実現された結果であったと考えられる.