Larger Number Of Tillers Research Articles

Spatial distribution of cereal aphids determines their abundance and population density in winter wheat stands

AbstractThe numbers per tiller (abundance) and per unit area of ground (population density) of the dominant cereal aphids in winter wheat crops, Sitobion avenae (Fabricius) and Metopolophium dirhodum (Walker) (Hemiptera: Aphididae) were recorded from 2000–2015. The results were used to test the hypothesis that at the population peak and 4 weeks previously, the population density of aphids in winter wheat crops (Triticum aestivum L., Poaceae) is uniformly distributed with respect to surface area and, as a result, their abundance is high in sparse stands (SPA) where the colonizing aphids are scattered among a small number of tillers (ca. 80 m−2), and low in dense stands (DEN) where they are scattered among a larger number of tillers (ca. 440 m−2). This prediction was verified for S. avenae, the population density of which did not significantly differ between SPA and DEN stands throughout this period. This species feeds mainly on the ears, whose nutritional quality for aphids varies little with crop density and during the course of ripening. In contrast and contrary to our prediction, the population density of M. dirhodum increased throughout this period more rapidly in SPA than in DEN stands. This species lives on leaves whose quality is better and remain present for longer during the course of ripening of the crop in SPA than DEN stands. The abundance of both species was higher in SPA than in DEN stands. Greater direct damage to cereal crops can be expected when using technologies and cultivars of winter wheat that need to be planted sparsely.

Chinese oats in temperate Bhutan: Results of field experiments

Abstract Seven varieties of forage oats from China were evaluated in the temperate environment of Bhutan for morphological traits, dry matter production, and forage quality. The oat variety Qingyin No. 1 provided a greater plant height (61 cm) and the largest number of tillers per plant (five tillers per plant). The leaf-stem ratio (LSR) was highest for Longyan No. 2 (LSR 0.73). During harvest in late winter, Longyan No. 2 had a greater plant height (64 cm) and the highest number of tillers per plant (seven tillers per plant), followed by Qingyin No. 1. The top three varieties with high LSRs of 1.49, 1.31, and 1.35 were Longyan No. 1, 2, and 3, respectively. In both summer and winter, Longyan No. 2 had the highest forage yields of around 5.00 and 4.00 DM t/ha, respectively. Qingyin No. 1 was the second largest forage producer, with under 5.00 DM t/ha in summer and under 3.00 DM t/ha in winter. For forage quality, Longyan No. 2 and Longyan No. 3 had the highest levels of crude protein (15%) in summer. However, during late winter, the Linna variety had the highest crude protein content (13%). The overall results of the field experiments suggest that Longyan No. 2 and Qingyin No. 1 are promising new oat varieties for winter fodder production in the temperate environments of Bhutan.

Field Performance of Disease-Free Plants of Ginger Produced by Tissue Culture and Agronomic, Cytological, and Molecular Characterization of the Morphological Variants

Ginger (Zingiber officinale Rosc.) is an important spice crop valued for its flavored and medical properties. It is susceptible to soil-borne diseases, which can cause considerable economic loss to growers. In vitro culture is feasible for the propagation of disease-free ginger plants, but has several disadvantages when producing seed rhizomes that can be commercially used, such as long cultivation cycles (usually 2–3 years) and occurrence of somaclonal variation. In this study, dynamic changes in the morphological characteristics of in vitro-propagated disease-free plants of ‘Wuling’ ginger were evaluated by continuous observation and measurement at 30-day intervals, and morphological variants were screened and characterized by agronomic, cytological, and molecular analysis at harvest. Results showed that the plants grew rapidly within 120 days after planting, and the most active growth period was from 60 to 120 days. Eight plants with clear and stable morphological differences were screened out from approximately 2000 plants grown in the field, and they could be classified into two groups (VT1 and VT2) based on tiller number, plant height, leaf color, and leaf shape. By flow cytometry analysis and chromosome counting, the VT1 was confirmed to be diploid, with the shortest plant height, the largest number of tillers and rhizome knobs, and the smallest tiller diameter and rhizome size among the three types of plants. The VT2 was mixoploid, consisting of diploid and tetraploid cells, with significantly reduced tiller number and rhizome knobs, significantly larger stomatal guard cells/apertures, and significantly lower stomatal density. SSR analysis detected DNA band profile changes in six out of the eight variants, including one plant of the VT1 and all the VT2 plants. The findings of this study might contribute to the commercial production of disease-free seed rhizomes in ginger, and the characterized somaclonal variants could provide useful germplasm resources for future breeding.

Relationship Between Distribution of the Radicular System, Soil Moisture and Yield of Sugarcane Genotypes

The objective of the study was to associate soil moisture, aerial biometric characteristics, and root distribution patterns in the yield of sugarcane genotypes in the fourth ratoon and the relationships between these characteristics. We used five sugarcane genotypes (CTC9002, RB044311, RB044313, RB044336, and RB867515) and five soil depths (0–20, 20–40, 40–60, 60–80 and 80–100 cm deep). The evaluations were carried out in December 2019. We evaluated the root systems, the soil water content at the five depths, the aerial biometric characteristics, and the productive yield. In the roots, the genotypes RB044311, RB044313, RB044336, and RB867515 showed a higher yield. On average, genotypes showed 50% of dry weight and total root length at a depth of 0–20 cm, 73% between 0 and 40 cm, and 86% between 0 and 60 cm. The RB044336 genotype showed maximum height and number of buds. The RB867515 genotype had the largest average stem diameter and CTC9002, the largest number of tillers. The genotypes CTC9002 and RB867515 presented the highest soluble solids' content, apparent sucrose in the juice, and total reducing sugars. These genotypes showed a 26% and 57% higher root density in soil layers at depths of 60–80 cm, respectively, 79% and 86% in the 80–100 cm layer, about the layer with the highest concentration of 0–20 cm roots. These layers remained with the highest soil moisture levels during the period of establishment and intensive cultivation growth. Thus, there was a relationship between root distribution dynamics and soil moisture in different areas.

Application of paddy planting calendar (KATAM) in Bengkayang District, West Kalimantan, Indonesia

The rice field harvested area in West Kalimantan decreases each year around 0.96 kw/ha from 2013. The decline in rice production is due to climate change. The objective of this study to determine the potential and constraints of developing Planting Calendar (KATAM) to anticipate the impact of climate change in West Kalimantan. The study was conduct in Tujuh Belas Sub District, Bengkayang District, West Kalimantan from January to December 2018. This study was performed using demonstration plot by comparing the existing farming system, KATAM, and introduced technology. The analysis used a randomized block design (RBD), where each treatment was repeated 3 times. The result showed that the vegetative parameters for the height of the existing treatment were higher than other treatments (76.40 cm). For the parameters of the number of tillers, KATAM and Introduction pattern had a large number of tillers, namely around 18 per plant. The treatment with KATAM pattern also had a high number of pithy unhulled grains and low unhulled rice (139 and 42 unit/penicle). The weight of 1000 seeds and yield per hectare, the treatment using KATAM pattern had a higher weight and yield (27.07 gr and 5.30 ton / ha).

Growth and productivity of new superior rice varieties and respondents’ preference in Majalengka Regency

In developing new superior rice varieties, farmers’ preferences are important things to study and high yield potential. The study aimed to obtain new superior varieties of adaptive rice based on plant growth and productivity performance and determine respondents’ preferences for the varieties studied. The study was conducted in rainfed rice fields, Majalengka Regency, West Java Province, from April to August 2020. The study used a randomized block with 6 treatments: Inpari 32 varieties, Inpari 39, Inpari 42, Inpari 43, Pajajaran, and Siliwangi, and repeated 5 times. The observed parameters consisted of: growth, yield components, and yields were analyzed by ANOVA followed by Duncan’s Multiple Range Test at a 5% level. The respondent’s preference test for grain and rice and organoleptic characters used a Likert scale and analyzed non-parametrically (Friedman test). The results showed that the Inpari 43 variety gave the highest yield. Still, farmers preferred the Inpari 32 variety to be developed because it has characters favored by farmers (respondents), namely short plant height, a large number of tillers, thin grain shape, white rice color, and fluffier rice taste.

Tillering and Structural Characteristics of Panicum Cultivars in the Brazilian Semiarid Region

Panicum maximum grasses are among the most used in Brazil because they have high forage production potential, nutritional value and adaptation to different climate conditions and in poor soils, which have been improved by the application of dolomitic limestone and nitrogen fertilizers and K2O, P2O5. The aim was to evaluate the tillering capacity and structural characteristics of six cultivars of Panicum maximum in the Brazilian semiarid region. The test was configured as a randomized block design with six treatments—the cultivars Aruana, Massai, Mombaça, Tamani, Tanzânia, and Zuri—and four replications. The studied variables included tiller population dynamics, tiller population density (TPD), appearance rate (ApR), mortality (MorB), tiller survival (SuvP), tiller stability index, height, light interception (LI), forage mass (FM), and morphological constituents. As to the population dynamics of tillers, seven generations were evaluated, and the largest number of tillers was observed in the first generation, regardless of the cultivar. Furthermore, the Massai cultivar demonstrated the highest TPD in all generations. Interaction between the cultivar and evaluation period was noted for ApR: the cultivars Tamani and Tanzânia indicated higher ApR at 122 and 137 days after establishment. The cultivar (P = 0.380) and evaluation period (P = 0.4469) had no effect on SuvP; however, higher MorB was detected in the cultivars Aruana and Tamani compared to Mombaça and Zuri, with intermediate values detected in the other cultivars. The highest FM was observed in the cultivars Massai, Mombaça, and Tamani, as well as in the leaf blade of Massai and Mombaça. The cultivars Massai, Mombaça, Tamani, Tanzânia, and Zuri have the potential to be cultivated in areas with marked water deficit and high temperatures, such as the Brazilian semiarid region. The cultivar Massai has a rapid recovery after a period of water scarcity. The cultivar Aruana is not recommended for use in the Brazilian semiarid region under rainfed conditions.

Indigenous Knowledge Cultivation of Local Rice Varieties “Siam Mutiara” and “Siam Saba” at Tidal Swampland

Tidal swampland at present and in the future is very strategic as one of the national food barns considering sloping of productive land. In South Kalimantan, for example, tidal swamp paddy fields are available which is quite large, but the most are still planted with local varieties. More than 70% of rice cultivation in the tidal swampland is planted with various local varieties. The existence of local rice varieties is inseparable from its adaptability and acceptability factors. Among local varieties that are popular and widely planted by farmers are Siam Saba and Siam Mutiara varieties. Siam Saba and Siam Mutiara were released as local-improved varieties. Both of these varieties have their respective advantages, both from the distribution of plant adaptation and the potential benefits of yield. Siam Saba variety is widespread in tidal swampland of acid sulfate soil types and soils that are seawater intrusion in the dry season (near the coast) with A/B overflow type, while Siam Mutiara in acid sulfate tidal paddy fields with B / C overflow type. Some of the advantages of Siam Saba compared to other local varieties are high yield potential of 4.70 t / ha, a large number of tillers, small and slender grain shape, white rice color, and amylose content of 81.69%. Whereas improved of Siam Mutiara is high yield potential of 4.80 t / ha, the color of clean yellow grain, the color of clear and translucent rice such as pearl, and amylose content of 48.88%. Both varieties showed uniform in growth, flowering time, and ripening simultaneously, in mature panicles with almost no green grains, and a high percentage of unfertile grains. Local rice cultivation technology (Siam Saba and Siam Mutiara) indigenous knowledge here includes seedbed, transplanting, land preparation, fertilizing, pest disease control, harvest, and post-harvest processing or yields carried out by indigenous farmers. This indigenous cultivation technology until now in tidal swamp paddy fields of South Kalimantan is still widely practiced by farmers, especially for ownership of narrow or limited rice fields. There were advantages and disadvantages of each in the practice of indigenous cultivation technology.

Morphological changes recorded in different phenophases of sugarcane plants subjected to water stress in tropical field conditions

Nowadays, water deficit is one of the major environmental stress issues affecting sugarcane crops around the world. It has been causing significant production decrease due to the increased mortality rates generated by water stress in sugarcane plantations. The aim of the current study is to assess sugarcane morphological and yield responses during different phenophases of sugarcane varieties when plants are subjected to drought stress in the fields of a tropical region. Six sugarcane varieties, namely: SP79-1011, RB855113, RB92579, RB867515, RB72454, and RB855536, were subjected to water stress. The herein adopted water regimes were (i) irrigated crop and (ii) crop subjected to natural drought in the field. Plants were cultivated under water stress imposition throughout three phenological stages (i) tillering, three months after planting; (ii) intense growth, seven months after planting; and (iii) ripening, eleven months after planting. The irrigation treatment consisted of supplementing the crop with 50 mm of water per month during the dry season, whereas non-irrigated plants were naturally grown under water stress conditions throughout the experiment. Water stress mostly affected the sugarcane crop during the intense growth phase. Varieties RB72454 and RB855536 presented smaller green-leaf number, as well as narrower leaf width and smaller leaf area under water stress; besides, they showed low productive potential and high stress susceptibility index (SSI). Stalk height maintenance and the larger number of tillers in RB92579 plants subjected to water stress helped balancing yield rates. This variety also showed the best drought tolerance (DTI) and yield/tolerance indices (YTI); moreover, the principal component analysis evidenced that leaf area, plant height and yield were important factors to distinguish the most tolerant varieties. Such results show that RB92579 is more drought tolerant and has better physiological acclimation potential than the other five varieties; therefore, it can be recommended for crops subjected to drought periods.

Hasil Padi Hibrida Genotipe T1683 pada Berbagai Dosis Pupuk NPK

<p>Hybrid rice has genetic traits such as sturdy stems, long and bushy dwarfs, short lifespan of 110-145 days, has large number of tillers, and leaves are dark green. Productivity of hybrid rice reached 6-12 tons-1ha. To obtain maximum production, hybrid rice varieties should be planted on fertile land, nutrients must be available, adequate irrigation, integrated pest management, and crop management should be done well. Efforts that can be done is to provide a balanced fertilizer, one with the use of appropriate doses of NPK fertilizer. The research was conducted in Gedangan Village, Grogol District, Sukoharjo Regency in May to August 2017 using Randomized Complete Block Design (RCBD) design with 2 factors of treatment, is the dosage of NPK fertilizer and rice varieties and replicates 4 times. The results showed that the treatment of various doses of NPK fertilizers and rice varieties increased the results of all observation variables, except in the variable of plant height and yield per harvest. While the interaction between the two treatments almost increased the results of all observation variables except for plant height and yield per harvest.</p>

PARTICIPATORY VARIETAL SELECTION WITH IMPROVED PEARL MILLET IN WEST AFRICA

A reconnaissance survey and participatory varietal selection trials (PVS) were conducted in four major pearl millet-growing countries of the Sahel between 2001 and 2003. The studies aimed to identify farmers' preferences in improved pearl millet varieties, increase awareness, test new varieties and enhance farmers' access to the improved varieties. Farmers selected five out of 10 tested varieties, with preferred characteristics, namely, maturity cycles of 80–90 d in the Sahel and 90–100 d in the Sudanian agro-ecozones, acceptable grain yield, compact and long (30–100 cm) panicles, a large number of tillers with panicles, adaptation and an acceptable taste. Farmers indicated that their local varieties were of superior adaptation and taste. They mentioned that hindrances to uptake and sustained use of improved varieties were due to lack of awareness, traditional values, seed unavailability, early maturity, bird damage and lack of fertilizer. The strong genotype × environment interactions in the Sahel suggests that breeding should be directed towards producing varieties adapted to specific zones rather than for wide adaptation. Notably, since farmers often cultivate pearl millet without any soil amendments, it may be advisable to disseminate varieties as a package (with fertilizer and agronomic instructions) rather than as varieties alone in a PVS programme, in order to achieve the full potential of improved varieties. The PVS trials are synergistic to plant breeding in identifying varieties suitable for harsh environments, which are difficult to duplicate in the research station. However, in the absence of formal distribution seed systems in the trial countries, village- or community-based seed production of varieties selected by farmers appears critical to the sustainable adoption of selected varieties.

Rice Morphogenesis and Plant Architecture: Measurement, Specification and the Reconstruction of Structural Development by 3D Architectural Modelling

The morphogenesis and architecture of a rice plant, Oryza sativa, are critical factors in the yield equation, but they are not well studied because of the lack of appropriate tools for 3D measurement. The architecture of rice plants is characterized by a large number of tillers and leaves. The aims of this study were to specify rice plant architecture and to find appropriate functions to represent the 3D growth across all growth stages. A japonica type rice, 'Namaga', was grown in pots under outdoor conditions. A 3D digitizer was used to measure the rice plant structure at intervals from the young seedling stage to maturity. The L-system formalism was applied to create '3D virtual rice' plants, incorporating models of phenological development and leaf emergence period as a function of temperature and photoperiod, which were used to determine the timing of tiller emergence. The relationships between the nodal positions and leaf lengths, leaf angles and tiller angles were analysed and used to determine growth functions for the models. The '3D virtual rice' reproduces the structural development of isolated plants and provides a good estimation of the tillering process, and of the accumulation of leaves. The results indicated that the '3D virtual rice' has a possibility to demonstrate the differences in the structure and development between cultivars and under different environmental conditions. Future work, necessary to reflect both cultivar and environmental effects on the model performance, and to link with physiological models, is proposed in the discussion.

Designing crop technology for a future climate: An example using response surface methodology and the CERES-Wheat model

Future crop production will be adapted to climate change by implementing alternative management practices and developing new genotypes that are adapted to future climatic conditions. It is difficult to predict what new agronomic technologies will be necessary for crop production under future climatic conditions. The purpose of this work was to develop an approach useful in identifying crop technologies for future climatic conditions. As an example of the approach, we used response surface methodology (RSM) in connection with the CERES-Wheat model and the HADCM2 climate simulation model to identify optimal configurations of plant traits and management practices that maximize yield of winter wheat in high CO 2 environments. The simulations were conducted for three Nebraska locations differing in altitude and rainfall (Lincoln, Dickens and Alliance), which were considered representative of winter wheat growing areas in the central Great Plains. At all locations, the identified optimal winter wheat cultivar under high CO 2 conditions had a larger number of tillers, larger kernel size, fewer days to flower, grew faster and had more kernels m −2 than the check cultivar under normal CO 2 conditions. In addition, optimal sowing dates were later and optimal plant densities were smaller than under normal conditions. We concluded that RSM used in conjunction with crop and climate simulation models was useful in understanding the complex relationship between wheat genotypes, climate and management practices.

Sterility of Thermo-Sensitive Genic Male Sterile Line, Heterosis for Grain Yield and Related Characters in F1 Hybrid Rice (Oryza sativa L.)

The thermo-sensitive genic male sterile (TGMS) T29s line was sterile when exposed to daily mean temperatures of 24.1°C or above during the critical stage (from 15 to 11 days before heading). It was completely sterile for both pollen and spikelet when the plant headed from June 16 to November 7 in Okinawa, because the temperature exceeded 24.1°C. The heterosis of the F1 hybrids between the T29s line and seven indica cultivars was examined. Most of the F1 hybrids showed positive heterosis over the male parent for grain yield per plant and the number of spikelets per panicle, and one of them manifested heterosis for grain yield over a F1 hybrid from a cytoplasmic male sterile (CMS) line. Dry matter accumulation per plant at the panicle initiation stage in most F1 hybrids was higher than that in the respective male parent or mid-parent, and it was correlated with a larger number of tillers and leaf area per plant. All F1 hybrids produced a larger number of panicles per plant than their respective male parent. Positive heterosis over the male parent for the number of filled grains per panicle, 1000-grain weight and harvest index was obtained in several F1 hybrids. A positive correlation was found between grain yield and the dry matter accumulation per plant in F1 hybrids. Both the larger number of panicles per plant and the larger number of spikelets per panicle were more important for the positive heterosis for grain yield in F1 hybrids rather than the higher 1000-grain weight. Among the yield attributes, a larger number of filled grains per panicle mainly contributed to a higher grain yield of F1 hybrids.

Varietal Differences in Tillering and Yield Responses of Rice Plants to Nitrogen-Free Basal Dressing Accompanied withSparse Planting Density in the Tohoku Region of Japan

At present, the main challenge in rice production is to achieve a high and stable yield with low input. In this study, the growth of tillers and yield of 12 rice cultivars and lines in the practice of nitrogen-free basal dressing with sparse planting density (BNo) was examined and compared with those in the conventional cultivation (CONT). The results in 1999, 2000 and 2001 showed that the numbers of both primary and secondary tillers m−2 were smaller in BNo than in CONT for all cultivars. However,ǽa large number of tillers in CONT, especially the secondary tillers, were nonproductive, and most of those in BNo were productive. The difference between BNo and CONT in the number of panicles m−2 was larger for the cultivars of the panicle-number type than for those of the panicle-weight type. Grain yield was often lower in BNo than in CONT, and the yield averaged over years and cultivars was 748 g m−2 in BNo and 772 g m−2 in CONT (the ratio of value in BNo to that in CONT was 97 %). The differenceǽbetween BNo and CONT in grain yield varied with the cultivar and the year. Under favorable weather conditions in 2000 and 2001, grain yield was high in both CONT and BNo, and was higher in CONT than in BNo for most cultivars. Nevertheless, under the unfavorable weather condition in 1999, grain yield was low in both CONT and BNo, and was similar or higher in BNo than in CONT. In all 3 years, the grain yield of Akitakomachi and Fukuhibiki was lower, and that of Ouu316 and Hitomebore tended to be higher in BNo than in CONT. The practice of BNo was found to be effective for achieving a stable and high yield of Ouu316 and Hitomebore in the Tohoku region.

The ecology and growth patterns of Cleistogenes species in degraded grasslands of eastern Inner Mongolia, China

Summary Cleistogenes is an important perennial grass genus found in the pastoral steppes of eastern Inner Mongolia. Despite its dominance in many grassland types, the value of Cleistogenes as a key genus for sustainable grassland development has only recently been recognized. To understand better how to manage Cleistogenes‐dominant grasslands, an experiment was conducted in China, to characterize the growth patterns of two Cleistogenes species (C. polyphylla and C. squarrosa) in relation to environmental parameters. Sampling exclosures were established on uniform grasslands at Mangha and Liuhe gachas. Over two growing seasons (1999–2000) vegetation cover, green and dry biomass by species, species height and tiller density of Cleistogenes were measured at about monthly intervals starting in mid‐May and ending in mid‐October. Cleistogenes polyphylla at Mangha and C. squarrosa at Liuhe accounted for > 50% of green biomass. Neither species made any significant growth before late June, even though soil moisture was available and a large number of tillers were present that had survived the subzero winter intact. In contrast, other species (Prunus sibirica, Potentilla spp. Aneurolepidium chinense) produced up to 500 kg ha−1 biomass in early spring. A relationship between temperature and green weight (wt) tiller−1 indicated that Cleistogenes required an average air temperature > 20 °C to initiate growth, most probably due to its C4 photosynthetic pathway. In this region, temperatures above 20 °C also coincide with periods of most reliable rainfall, which may explain the success of Cleistogenes in grassland degraded by overgrazing. In contrast, competing C3 species (e.g. Stipa spp. and Aneurolepidium chinense) initiate growth earlier in spring when rainfall is highly variable and when small plants are most exposed to severe grazing pressure by livestock emerging from winter in poor condition. Where Cleistogenes spp. completely dominated the grassland, the length of the growing season was shorter and feed shortages in early spring became more acute than for grasslands dominated by C3 species. Livestock producers can minimize this effect by adopting management tactics such as resting pastures in spring to maintain a balance between C3 and C4 perennial grasses. Further research is needed to establish when grazing and strategic rest have most impact on the stability of Cleistogenes‐dominant grasslands.

SIMULATION AND RESPONSE SURFACE METHODOLOGY TO OPTIMIZE WINTER WHEAT RESPONSE TO GLOBAL CLIMATE CHANGE

Future climate changes can have a major impact on crop production. But, whatever the climatic changes, crop production can be adapted to climate change by implementing alternative management practices and developing new genotypes that will take full advantage of the future climatic conditions. Since the classical agronomic research approach is not possible in identifying these new agronomic technologies for the future climatic conditions, we used response surface methodology (RSM) in connection with the CERES-Wheat crop model and the HADCM2 climate simulation model to identify optimal configuration of plant traits and management practices that maximize yield of winter wheat under high CO2 environments. The simulations were conducted for three Nebraska locations (Havelock, Dickens and Alliance), which were considered representative of winter wheat growing areas in the central Great Plains. At all locations, the identified optimal winter wheat cultivar under high CO2 conditions had a larger number of tillers, larger kernel size, shorter days to flower, grew faster and had more kernels per square meter than the check variety under normal CO2 conditions, while the optimal planting dates were later and planting densities were lower than under normal conditions. We concluded that RSM used in conjunction with crop and climate simulation models was a useful approach to understanding the complex relationship between wheat genotypes, climate and management practices.

Spikelet numbers, sink size and potential yield in rice

A new plant type (NPT) has been developed at the International Rice Research Institute (IRRI) using tropical japonica germplasm in an attempt to increase yields. In direct contrast to high yielding indicas, which have large numbers of tillers and relatively small panicles, the NPT has large panicles and low tiller numbers. To determine whether the NPT had a higher potential for spikelet production, and possibly yield, than an elite indica, the total number of juvenile spikelets (glumous flower primordia) was determined for plants grown in the field as a crop or widely spaced. The maximum number of juvenile spikelets produced by the temporal pattern of tillers in a hill was recorded at the time of late differentiation of each tiller’s panicle. The number was greater for spaced plants than crop plants and it decreased linearly with tiller age. For crop plants approximately one juvenile spikelet was produced per square centimeter of leaf area. In 1997, a large number of the juvenile spikelets were lost before harvest, that number increased significantly in the wetter year of 1999. To quantify potential yield and its reduction by the loss of spikelets between the juvenile and mature stages, the number of spikelets at harvest and the filled fraction (grains) was determined for each tiller and a simple empirical model of yield was constructed. The model predicted that if all of the juvenile spikelets were to be transformed into grains a potential yield more than double the actual yield would be produced in crops of high yielding indicas or the NPT, suggesting that source strength rather than sink size limited yield in this study. Differences in spikelet number at harvest could be offset by differences in individual grain weight and percentage filling of spikelets. Even in rice crops grown with large applications of fertilizer, at current atmospheric concentrations of CO 2, yields are limited by the supply of resources necessary for the development and synthesis of the grain rather than sink capacity. The potential sink size of the crop is almost double that actually realized, even though the productive tillers of crop plants do not reach their full potential for spikelet production compared with spaced plants.

Comparison of growth and 15nitrogen recovery between direct seeded flooded and transplanted rice at early growth stage under conventional and delayed planting

In the tropics, broadcast seeded flooded rice (BSFR) was found to show a higher 15N recovery than transplanted rice (TPR) under the same fertilizer N management conditions mainly due to the higher initial growth rate at early stages as a result of the lack of transplanting shock. This study was conducted to compare the growth characteristics and 15N recovery at early growth stages between BSFR and TPR under conventional and delayed (low and high temperatures) planting environment in Japan. Under both planting environments, BSFR produced a larger number of tillers m-2 (600-700) than TPR (420-450) at the middle growth stage (89 d after seeding, DAS). However, TPR showed a larger crop dry weight accumulation at either planting time resulting in a higher total plant N uptake. Irrespective of the cropping method and time, dry weight was exponentially correlated with the plant uptake while 15N recovery showed a curvilinear relation to the N uptake. Under conventional planting, TPR showed a higher basal 15N recovery (ranging from 23-28%) than BSFR (13-16%) in 1996 while the values were 24- 26% for TPR and 14-23% for BSFR in 1997 during the maximum tiller (60- 69 DAS) to panicle formation stages (85-89 DAS). Under delayed planting, still TPR showed a higher average basal 15N recovery (28%) than BSFR (23%) at the same stages as those mentioned above. These results suggest that regardless of planting time in Japan, TPR exhibited a higher initial growth rate than BSFR resulting in higher use efficiency of both soil and fertilizer N at the early growth stages.

Effects of defoliatingStipa tenuisandPiptochaetium napostaenseat different phenological stages: axillary bud viability and growth

The size and number of axillary buds at various degrees of respiratory activity, and their relationship to the re-establishment of photosynthetic surface area after a single annual defoliation during different phenological stages were determined for two perennial tussock grasses,Stipa tenuisandPiptochaetium napostaense, under rain-fed conditions. Treatments were repeated annually on the same plants and their responses evaluated during 1991–1993.Bud respiratory activity was examined using the tetrazolium test and the vital stain Evans' blue which allowed separation of the bud pool at any stem base into three categories of bud viability: metabolically active, dormant and/or dead.At the end of the second season of successive defoliations, plants of both species that had defoliated late or after internode elongation had a greater number of respiratorily inactive buds than undefoliated plants or plants defoliated at the vegetative stage. This must have contributed to the lower production of dry matter after clipping on later rather than earlier defoliated tussocks. The effects of late defoliations on bud metabolic activity, however, were only transient. At the beginning of the growing season following two consecutive years of treatments, the proportion of previous-year stem bases which had produced green tillers, and the number of metabolically active axillary buds and green tillers of similar height plus total green leaf length and number, and subsequent tiller number and dry weight per plant, were similar under all defoliation treatments. Even when stem bases of these species had only two to three axillary buds, the large number of tillers that can be produced per stem base (up to 20 daughter tillers) must help these species to rapidly re-establish a photosynthetic canopy after defoliation and allow them to persist in communities which have been exposed to overgrazing for several decades.