Higher Relative Growth Rate Research Articles

Contrasting responses to water-deficit among Encelia canescens populations distributed along an aridity gradient.

Drought is the most limiting factor for plant growth and recruitment in arid environments. For widespread species, however, plant responses to drought can vary across populations because environmental conditions can vary along the range of the species. Here, we assessed whether plants of Encelia canescens from different populations along an aridity gradient in the Atacama Desert respond differently to water-deficit conditions. We conducted a common-garden experiment using plants grown from seeds from three populations distributed along an aridity gradient to test for differences in relative growth rate (RGR), biomass, root to shoot ratios, and photosynthesis between watered and water-deficit plants. Additionally, we examined the relationship between root to shoot ratios with RGR and total plant biomass along the gradient. Water deficit affected root to shoot ratios, biomass, and RGR, but not photosynthesis. Populations varied in RGR and biomass; plants from the most arid population had higher RGRs, but lower biomass than those from the least arid population. In watered conditions, root to shoot ratios did not vary with RGR or biomass. Conversely, with the water deficit, root to shoot ratios were negatively and positively related to biomass and RGR, respectively. Response to water deficit differed among E. canescens populations; plants from the lowest rainfall environment adjusted root to shoot ratios, which may have allowed for equal biomass production across treatments. In contrast, plants from the wettest population did not adjust root to shoot ratios, but were reduced in biomass. These morphological and physiological changes to water availability showed that populations can use different strategies to cope with water deficit.

Effect of apple growth pattern on fruit textural quality at harvest and after cold storage in cv. ‘Braeburn’

We have studied the effect of fruit growth pattern on apple (cv ‘Braeburn’) textural quality evaluated by near infra-red spectroscopy at harvest and by sensorial analysis with a trained panel both at harvest and after two months of cold storage. Fruit growth pattern was defined considering two main growth phases and using absolute and relative growth rate as growth parameters. Fruit with similar size at harvest, as well as fruit with low absolute growth rate during cell division and high relative growth rate during cell expansion exhibited significant differences in juiciness score at harvest and a significant increase in mealiness after storage. Results obtained by near infra-red spectroscopy tended to confirm the effect on juiciness at harvest. Different hypotheses were proposed to explain these results in terms of cell size or cell wall proprieties. Though preliminary and subject to confirmation, these results tend to indicate that growth pattern could be used as an integrative indicator to discriminate textural fruit quality in apple.

English

Studies quantifying the effect of the nitrogen over the growth of genotypes of Conilon coffee contribute to improve the fertilization management. Thus, this study was developed to evaluate the growth of improved genotypes of Coffea canephora Pierre ex Froehner submitted to nitrogen fertilization. Six improved genotypes of C. canephora, from different groups of ripening cycles, were grown without nitrogen fertilization or with fertilization at level of 0.625 g kg-1 of soil, cultivated in greenhouse, following a completely randomized design, with four replications. The plant growths were evaluated considering the plant height, stem diameter, number of leaves and relative growth rate. Nitrogen fertilization was able to promote higher growth, as well as, in general, a higher relative growth rate of all genotypes. Differentiation among genotypes was observed for their responses to each of the evaluated parameters. Noteworthy are the genotypes 77, in leafiness, and 67 in plant height and stem diameter, which presented higher growth compared to other genotypes, with or without nitrogen fertilization. Key words: Coffea canephora, response, deficiency, mineral nutrition.

Effects of cast properties and passage through the earthworm gut on seed germination and seedling growth

Success of seed germination and seedling establishment is potentially affected by interactions with earthworms. Two of the possible mechanisms that might explain such impact are the selective ingestion of seeds by earthworms that might break seed dormancy, and germination in their nutrient-rich casts. The aim of this study was to disentangle the effect of seed passage through the earthworm gut and the effect of cast alone, as a germination medium, on the germination and growth of four herbaceous species. We hypothesized that the presence of seeds in casts facilitates their germination and seedling growth and that the passage of seeds through gut favors seed germination. Non-ingested seeds were placed in artificial earthworm casts shaped from cast material of 3 soil types×3 earthworm species combinations (plus control). Seed germination after seed ingestion and excretion was tested in a Petri dish experiment in the presence of each earthworm species. Contrary to our expectations, we found that passage of seeds through the gut of Lumbricus terrestris decreased the germination of Festuca lemanii and that all seeds of Origanum vulgare and Urtica dioica were digested. Total seed germination of non-ingested seeds placed in casts was affected by cast properties, i.e., by the interaction between the soil type and the earthworm species. Seedlings germinating from the control material had a higher relative growth rate than in material from Allolobophora chlorotica cast. Our results suggest that seed ingestion alters seed germination success of specific plant species. The cases of lower germination and seedling growth induced by cast effects are discussed with regards to their physical, chemical and microbiological properties.

Growth performance of unialgal gametophytes of the brown alga Saccharina japonica in mass culture conditions

For the purpose of mass culture of Saccharina japonica unialgal gametophytes originated from spores in laboratory conditions to breed sporelings, a series of experiments were designed to evaluate vegetative growth performance of male and female gametophytes. After 8-day culture, female gametophytes exhibited the higher relative growth rates (RGRs) around 8.29–9.27 % day−1 than male ones (5.30–6.10 % day−1). Both male and female gametophytes had the higher RGRs in NO3−-supplemented medium than that in NH4+ medium under equal nitrogen concentration. The RGRs of the female and male could reach the peak levels of 8.96 and 5.91 % day−1 in NO3− group and 6.60 and 3.89 % day−1 in NH4+ group, respectively. Elevation of temperature from 5 to 15 °C significantly promoted the vegetative growth of both in the medium enriched with 450 μM of NO3− or NH4+. At higher temperature (25 °C), the growth rates of both were retarded greatly with the female being more sensitive to the exposure to 450 μM of NH4+, and the photosynthesis activity was partially damaged as reflected by the decrease of the optimal chlorophyll fluroscence quantum yield (Fv/Fm) from 0.657 ± 0.023 to 0.401 ± 0.053.

Effects of nitrogen addition on the competition between the invasive species Flaveria bidentis and two native species

Flaveria bidentis (L.) Kuntze, an invasive plant in China, has caused serious environmental and agricultural problems. A competition experiment with and without nitrogen fertilizer under field conditions was conducted to determine the competitive ability of the invasive plant species with two native species. The results showed that fertilization only increase relative growth rate of F. bidentis in the monoculture and the photosynthetic rates of the invasive species when it competed with Abutilon theophrasti. The growth of Leonurus heterophyllus was inhibited, while the growth of A. theophrasti was promoted by competition with F. bidentis. Nitrogen fertilizer addition significantly decreased the positive effect and increased the negative effect on A. theophrasti. The higher relative growth rate and net assimilation rate might give A. theophrasti a competitive advantage in comparison to L. heterophyllus in the competition with F. bidentis due to its greater ability to utilize available resources.

Differential cadmium resistance of two morphologically distinct types of potato (Solanum tuberosum) callus

AbstractCallus culture has been used to study the cellular basis of sensitivity of plants to toxic trace elements including cadmium. Callus friability may be related to plant response to exposure to trace elements as callus friability is related to the plant cell wall which plays a role in resistance of plant cells to trace element toxicity. The aim of this study was to investigate the relationship between two types of potato callus with different friability and their sensitivity to cadmium. A high frequency (about 80%) of leaf or internodal explants of potato (Solanum tuberosum L., cv, Iwa) formed a friable, pale green callus (type-A callus) on half-strength basal Murashige and Skoog medium supplemented with 12.42 μM picloram. On medium supplemented with 4.43 μM 6-benzyladenine (BA) and 5.37 μM 1-naphthalene acetic acid (NAA), a compact, non-friable callus (type-B callus) was induced in about 80% of the explants. Type-B callus was greener than type-A callus. Callus formation in both the leaf and internodal explants were completely inhibited on the medium used for induction of type-A or type-B callus when the respective medium was supplemented with 54 μM cadmium chloride (Cd). The type-B callus was found to be more resistant (less necrosis and higher relative growth rates) to 27, 54, and 109 μM of Cd than the type-A callus. The type-B callus also exhibited a higher level of peroxidase activity (a marker antioxidant enzyme counteracting oxidative stress) than the type-A callus when cultured on these Cd concentrations. This is the first study showing the importance of callus friability in plant cell response to Cd treatment.

Effects of Amendments on Growth and Uptake of Cd and Zn by Wetland Plants, Typha angustifolia and Colocasia esculenta from Contaminated Sediments

A pot study was conducted to compare the effects of amendments (CaHPO4 and cow manure) on growth and uptake of Cd and Zn from contaminated sediments by two wetland plant species, Typha angustifolia and Colocasia esculenta. Contaminated sediments (Cd 33.2 mg kg–1 and Zn 363 mg kg–1) were collected from Mae Tao basin, Mae Sot district, Tak province, Thailand. The experiment consisted of 4 treatments: control (uncontaminated sediment), Cd/Zn, Cd/Zn + 5% CaHPO4, and Cd/Zn + 10% cow manure. Plants were grown for 3 months in the greenhouse. The addition of CaHPO4 resulted in the highest relative growth rate (RGR) and highest Cd accumulation in both T. angustifolia and C. esculenta while the lowest RGR was found in C. esculenta grown in the cow manure treatment. Both plant species had higher concentrations of metals (Cd, Zn) in their belowground parts. None of the amendments affected Zn accumulation. C. esculenta exhibited the highest uptake of both Cd and Zn. The results clearly demonstrated the phytoremediation potential of C. esculenta and the enhancement of this potential by CaHPO4 amendment.

Carbon acquisition strategies uncoupled from predictions derived from species life-cycle

We compare carbon use strategies of congeneric annual (P. gracilis and P. angustifolia) and perennial (P. mendocina and P. pinetorum) Physaria (Brassicaceae), to evaluate the relevance of eco-physiological traits as determinants of differences in growth and to add information on the current debate on the agro-ecological suitability of perennial species for grain production in low resource ecosystems. Because of differences in growth and in seed-output previously found within this genus, we hypothesized that C acquisition strategies would not be fully coupled with predictions derived from a species life-cycle. Further, we expected to find different suites of traits related to C-acquisition among perennial species of Physaria. We found species with high (P. gracilis and P. pinetorum) and low (P. mendocina and P. angustifolia) relative growth rate (RGR) and biomass. The variation in RGR was linked to differences in specific leaf area (SLA) and allocation to leaves (leaf mass ratio, LMR) and roots (root mass ratio, RMR), but not to the species life-cycle. Physaria gracilis had high allocation to leaf area (leaf area ratio, LAR), LMR, high SLA, and low RMR and carbohydrates reserves. The slow-growth strategy found in P. mendocina was linked to low LAR, low SLA and large below-ground allocation. The other species showed intermediate strategies between these two. The sets of traits present in P. gracilis and in P. mendocina are extremes in the C acquisition–conservation trade-off, and may allow them to cope with low resource environments in different ways. SLA, LMR and RMR were the main determinants of RGR, while total non-structural carbohydrates (TNC) and leaf longevity were linked to the life-cycle. Taken together these characters define the intermediate growth strategies of P. angustifolia and P. pinetorum. These intermediate strategies were not dependent on the species life cycle and support the hypothesis of uncoupled relationships between growth, C acquisition strategies and life-cycle.

Ecotypic variation in growth responses to simulated herbivory: trade-off between maximum relative growth rate and tolerance to defoliation in an annual plant.

It has been hypothesized that slow-growing plants are more likely to maximize above-ground biomass and fitness when defoliated by herbivores than those with an already high relative growth rate (RGR). Some populations of the annual herb Datura stramonium L. can tolerate foliar damage better than others. The physiological basis of this difference is examined here in a comparative study of two ecotypes that differ in tolerance and maximum growth rate, using a growth analytical approach. One hundred and fifty-four plants of each ecotype grown under controlled conditions were suddenly defoliated (35 % of total leaf area removed) and a similar sample size of plants remained undefoliated (control). Ontogenetic plastic changes in RGR and its growth components [net assimilation rate (NAR), specific leaf area and leaf weight ratio (LWR)] after defoliation were measured to determine whether these plastic changes maximize plant growth and fitness. Different ontogenetic phases of the response were discerned and increased RGR of defoliated plants was detected at the end of the experimental period, but brought about by a different growth component (NAR or LWR) in each ecotype. These changes in RGR are putatively related to increases in fitness in defoliated environments. At the intra-specific scale, data showed a trade-off between the ability to grow under benign environmental conditions and the ability to tolerate resource limitation due to defoliation.

Characteristics of growth and radial oxygen loss of eight wetland plants

湿地植物是人工湿地的核心部分,筛选优良的植物种类,将有利于充分发挥湿地植物的功能,提高人工湿地污水处理的能力.分析4种须根型植物香蒲(Typha orientalis)、美人蕉(Canna indica)、灯芯草(Juncus effusus)、纸莎草(Cyperus papyrus)和4种根茎型植物菖蒲(Acorus calamus)、再力花(Thalia dealbata)、芦竹(Arundo donax)、黄菖蒲(Iris pseudacorus)在厌氧、水培条件下的生长状况及根系泌氧特性;比较它们的根和茎叶生物量、相对生长速率(RGR)、根长、根孔隙度和泌氧量(率)等生理生态特性.结果表明,8种湿地植物在厌氧条件下生长状况良好;其中,须根型植物的生物量、RGR和泌氧能力均显著优于根茎型植物.在相同光照条件下,灯芯草的泌氧率最大,为192.62μmol O₂/(d·g (DW_root)),而黄菖蒲的根系泌氧率最小,仅为68.81μmol O₂/(d·g(DW_root)).各植物根系泌氧率大小为:灯芯草> 纸莎草> 香蒲> 美人蕉> 菖蒲> 再力花> 芦竹> 黄菖蒲.方差分析显示:植物根系泌氧率与根孔隙度呈极显著正相关,而植物泌氧量与RGR、各生物量呈极显著正相关,但与根茎比呈显著负相关.;Plant is the core component of constructed wetland. Selecting the superior varieties of wetland plants would make full use of their functions in constructed wetland, and then improve the efficiency of sewage water treatment. To investigate the growth characteristics and radial oxygen loss(ROL) from roots of wetland plants under extreme condition, 8 species of wetland plants which were cultured with synthetic water under anaerobic condition were collected for comparison. 8 wetland plants could divided into two groups, fibril-root plant(Typha orientalisl, Canna indica, Juncus effusus, Cyperus papyrus) and rhizomatic-root plant(Acorus calamus, Thalia dealbata, Arundo donax, Iris pseudacorus). The eco-physiological characteristics, such as biomass, relative growth rate(RGR) root length, root porosity, root ROL were compared. Results showed that 8 kinds of wetland plants all grown well under anaerobic conditions. Fibril-root plants had greater biomass, higher RGR and ROL than rhizomatic-root plant. Under the same illumination, Juncus effuses had the maximum ROL which reached 192.62μmol O₂/(d·g (DW_root)), while Iris pseudacorus had the minimum, which was only 68.81μmol O₂/(d·g (DW_root)). The ranking order of ROL of the 8 species wetland plants was: Juncus effuses> Cyperus papyrus> Typha orientalis> Canna indica> Acorus calamus> Thalia dealbata> Arundo donax> Iris pseudacorus. ANOVA analysis indicated that Rate of ROL was positively correlated with root porosity. The ROL was positively correlated with both of RGR and biomass,while negatively related to root/shoot ratio.

Effects Of Seed Vigor On Growth And Grain Yield Of Maize

Abstract Reduction in seed vigor is a consequence of seed aging which may influence field performance of crops. Thus, a field study was conducted as RCB design with 6 replicates to evaluate the effects of seed vigor on maize (cv. Ksc 301) growth and yield. A sub-sample of maize seeds was kept as control and two other sub-samples were artificially aged for 9 and 12 days. So, three seed lots (V1, V2 and V3), with different vigor were provided and sown in the field. Mean emergence time significantly increased, but mean emergence percentage decreased as seed vigor increased. The lowest leaf area index (LAI), dry matter accumulation (DMA) and crop growth rate (CGR) were obtained for plants from the lowest vigor seed lot (V3). At the later stages of growth, the highest relative growth rate (RGR) was recorded for V1 plants, followed by V2 and V3 plants. Poor stand establishment and growth of plants from V2 and V3 seed lots led to yield loss by 23.7 % and 41.5 %, respectively. These results showed that production and cultivation of high vigor seeds are necessary to ensure satisfactory field performance of maize.

Wastewater treatment using integrated anaerobic baffled reactor and Bio-rack wetland planted with Phragmites sp. and Typha sp.

The purpose of this study is to examine the potential use of anaerobic baffled reactor (ABR) followed by Bio-rack wetland planted with Phragmites sp. and Typha sp. for treating domestic wastewater generated by small communities (751 mg COD/L, 500 SCOD mg/L, 348 mg BOD5/L). Two parallel laboratory-scale models showed that the process planted with Phragmites sp. and Typha sp. are capable of removing COD by 87% & 86%, SCOD by 90% & 88%, BOD5 by 93% & 92%, TSS by 88% & 86%, TN by 79% & 77%, PO4-P by 21% & 14% at an overall HRT of 21 (843 g COD/m3/day & 392 g BOD5/m3/day) and 27 (622 g COD/m3/day & 302 g BOD5/m3/day) hours, respectively. Microbial analysis indicated a high reduction in the MPN of total coliform and TVC as high as 99% at the outlet end of the processes. The vegetated system using Phragmites sp. showed significantly greater (p <0.05) pollutant removal efficiencies due to its extensive root and mass growth rate (p <0.05) of the plant compared to Typha sp. The Phragmites sp. indicated a higher relative growth rate (3.92%) than Typha sp. (0.90%). Microorganisms immobilized on the surface of the Bio-rack media (mean TVC: 2.33 × 107 cfu/cm2) were isolated, identified and observed using scanning electron microscopy (SEM). This study illustrated that the present integrated processes could be an ideal approach for promoting a sustainable decentralization, however, Phragmites sp. would be more efficient rather than Typha sp.

Contribution of trehalose biosynthetic pathway to drought stress tolerance of Capparis ovata Desf.

Trehalose and the trehalose biosynthetic pathway are important contributors and regulators of stress responses in plants. Among recent findings for trehalose and its metabolism, the role of signalling in the regulation of growth and development and its potential for use as a storage energy source can be listed. The xerophytic plant Capparis ovata (caper) is well adapted to drought and high temperature stress in arid and semi-arid regions of the Mediterranean. The contribution of trehalose and the trehalose biosynthetic pathway to drought stress responses and tolerance in C.ovata are not known. We investigated the effects of PEG-mediated drought stress in caper plants and analysed physiological parameters and trehalose biosynthetic pathway components, trehalose-6-phosphate synthase (TPS), trehalose-6-phosphate phosphatase (TPP), trehalase activity, trehalose and proline content in drought stress-treated and untreated plants. Our results indicated that trehalose and the trehalose biosynthetic pathway contributed to drought stress tolerance of C.ovata. Overall growth and leaf water status were not dramatically affected by drought, as both high relative growth rate and relative water content were recorded even after 14days of drought stress. Trehalose accumulation increased in parallel to induced TPS and TPP activities and decreased trehalase activity in caper plants on day 14. Constitutive trehalose levels were 28.75 to 74.75μg·g·FW(-1) , and drought stress significantly induced trehalose accumulation (385.25μg·g·FW(-1) on day 14) in leaves of caper. On day 14 of drought, proline levels were lower than on day 7. Under drought stress the discrepancy between trehalose and proline accumulation trends might result from the mode of action of these osmoprotectant molecules in C.ovata.

Development, growth, and nitrogen use of autumn- and spring-sown facultative wheat

Spring-sown crops are expected to have a higher risk of drought during summer in the next decades in Central Europe due to expected climate change. Therefore, a two-year experiment was conducted under Pannonian growing conditions in Eastern Austria to investigate the effect of autumn- and spring-sowing of facultative wheat. Autumn-sowing of facultative wheat enhanced crop development, soil coverage, crop stand height, crop growth rate, and nitrogen (N) utilization efficiency during the vegetation period compared to spring-sowing; duration of growth stages was prolonged and crops were earlier ripe. In contrast, spring-sowing resulted in higher relative growth rates, higher N concentrations of aboveground dry matter, higher relative N uptake rates, and more mineral N in the soil. At harvest, grain yield and yield components ears m−2 and thousand kernel weight (TKW) were higher in autumn-sown than in spring-sown wheat, resulting thereby in an increased seed yield. Spring-sown wheat had higher N concentrations in grain and in straw. Anyhow, N yield was slightly higher with autumn-sowing due to the higher grain and straw yields. Grain and straw yield, plant stand height, ears m−2, and TKW were impaired in the second experimental year by a severe drought for both sowing dates as well as N concentrations and N yields of grain and straw, partial factor N use efficiency and N utilization efficiency. But the yield components harvest index, grains m−2, and grains ear−1 were strongly impaired with spring-sowing under drought conditions. Thus, autumn-sowing of wheat resulted in higher yield stability across both years, based on these yield components highlighting possible benefits of autumn-sowing with expected summer drought under climate change.

Seed size and recruitment limitation influence seedling establishment in three tallgrass prairie species

A seed size–seed number tradeoff predicts that large numbers of seeds have an establishment advantage under low levels of competition, while large seed size is advantageous under asymmetric competition. Testing these predictions in the context of tallgrass prairie restoration should increase predictability of outcomes of species composition—restoration technique combinations. I conducted field and greenhouse experiments comparing seedling establishment among three tallgrass prairie species with different seed mass-seed number combinations, but with similar mass of seeds sown. Species were prairie dock [Silphium terebinthinaceum, mass = 33.2 + 2.1 mg ( $$\overline{x}$$ + SE, n = 100)], wild quinine (Parthenium integrifolium, mass = 3.1 + 0.3 mg), and smooth blue aster (Symphyotrichum laeve var. laeve, mass = 0.53 + 0.02 mg). Seeds were sown into mowed or tilled plots with shade and mulch treatments in an old field in northeastern Illinois USA, and seeds were sown into containers with or without vegetative cover in a greenhouse. In mowed plots, species with larger numbers of seeds sown had higher seedling densities. In tilled plots, seedling densities of the large-seeded Silphium were reduced less by shade than the small-seeded Parthenium. Symphyotrichum, however, did not respond to treatments as expected based on its seed size. High relative growth rate possibly increased Symphyotrichum seedling establishment in competitive environments. Results of this study demonstrated recruitment limitation when seedlings established into existing vegetation, and suggest that species composition resulting from specific seeding rates during prairie restoration may be more predictable when species are interseeded into existing vegetation, than when seeds are sown into tilled fields.

Different Growth Partitioning and Shoot Production of &lt;i&gt;Talinum triangulare&lt;/i&gt; Treated with Organic and Inorganic Fertilizer

Talinum triangulare or waterleaf is an underutilized tropical plant, mostly found as weeds, and has been used more as medicinal plant than as vegetable in Indonesia. The study of Talinum triangulare cultivation has been explored to increase the shoot production as functional vegetables. The effects of organic fertilizer applications at 0.50, 0.75, 1.00, 1.25 and 1.50 of the standard rate on waterleaf growth were tested in a Leuwikopo research station, Bogor, West Java, Indonesia. Standard rate of organic fertilizer consisted of 12.3 t..ha-1 of cow manure, 226.8 kg. .ha-1 of guano, and 5.5 t.ha-1 of rice hull ash that is equal to 100 kg urea, 60 kg SP-36 and 100 kg KCl.ha-1. Net assimilation rate (NAR) of the organic fertilizer-treated plants was lower than the inorganic fertilizer-treated with plant at two to four weeks after planting (WAP). However, the plants treated with 0.75-1.25 organic fertilizer had a higher NAR than those treated with inorganic fertilizer at four to six WAP. Plants treated with 0.75 rate of organic fertilizer had similar relative growth rate (RGR) to plants treated with the inorganic fertilizer at two to four WAP, whereas plants treated with 1.00, 1.25 and 1.50 standard rate had higher RGR than plants treated with inorganic fertilizer at 4-6 WAP. Plants treated with 1.50 organic fertilizer rate had 34.55% more marketable shoots compared to those treated with inorganic fertilizer whereas those treated with 0.50 rate of organic fertilizer had 179.54% at 6 WAP. The percentage of marketable shoots to total fresh weight of the organic fertilizer-treated plants was lower than the inorganic fertilizer-treated plants.Keywords: Talinum triangulare, leafy vegetables, organic

Climate change and the potential spread of Sorghum halepense in the central area of Argentina based on growth, biomass allocation and eco-physiological traits

Despite the research dedicated to understand the potential climate change impacts on cropping systems, little attention has been given to potential effects on the geographic range of agricultural weeds. This paper reviews some biological and eco-physiological features of Sorghum halepense populations and their current and potential spread in a central eco-region of Argentina. Above ground biomass accumulation of the weed shows very high accumulation rates, which in the case of rhizomes is boosted as the available resources in propagule increases. An increase in temperature by 15 % may increase the relative growth rate (RGR) by 50 % in a 20–90 days growth period. Not only biomass output but also biomass allocation is directly related to adaptation in changing environments. Populations adapted to limited water conditions are able to maintain a higher RGR under water restriction as compared to those adapted to more humid conditions. Regarding the temperature, climate models are coincident: a range of increase from 0.9 °C in the south to 1.4 °C in the north of Argentina is predicted for 2020–2040, as compared to the period 1961–1990. Concerning the rainfall, not yet a prediction but a real fact is the displacement of isohyets from east to south. The average frequency of the weed in the pool of fields recently surveyed in the central region was 37 %, which increased to 42 % in the field borders. We consider that this frequency is high, since all crop fields are managed with high technology level and herbicides have been applied not only during the crop cycles, but also in previous fallows. The high RGR and other physiological features of weed populations at low water availability, which is more frequent in the west of the surveyed region where the frontier of extensive crops have recently displaced, may explain higher frequencies found. Well-adapted S. halepense populations invading rainfed crops in this eco-region will likely to take advantage under the forthcoming forecasted climatic conditions. Since temperatures increase from east to west as shown in climograms, S. halepense populations will likely perform even better under the new climate conditions. Coupling the actual management to physiological traits, it is envisaged an increase of the weed frequency in the surveyed eco-regions.

Physiological Attributes of Transplant &lt;i&gt;Aman&lt;/i&gt; Rice (Cv. Brri Dhan52) as Affected by Tiller Seedlings and Urea Super Granules

The experiment was conducted at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh, Bangladesh to investigate the effect of age of tiller seedlings, number of tiller seedlings hill-1 and application of urea super granules (USG) on some physiological attributes of transplant Aman rice cv. BRRI dhan52. The experiment consisted of two ages of tiller seedlings viz. 25- and 35-day old, three levels of tiller seedlings hill-1 viz.1, 3 and 5 seedlings hill-1 and three USG levels viz. 0, 1.8g and 2.7g USG per four hills in every alternate row. The experiment was laid out in a randomized complete block design with three replications. The effect of age of tiller seedlings, number of tiller seedlings hill-1 and USG application were significant on crop growth rate (CGR), relative growth rate (RGR), net assimilation rate (NAR) and leaf area index (LAI). The highest CGR and RGR were found by transplanting 35-day old tiller seedlings during the period at 15-30 and 60-75 DAT when 5 tiller seedlings hill-1 were transplanted. The highest NAR was observed at 60-75 DAT with transplanting 5 tiller seedlings hill-1 and the lowest one was recorded at 30-45 DAT. The highest LAI was found at 35-day old tiller seedlings during the period at 60 and 75 DAT when 5 tiller seedlings hill-1 were transplanted. CGR and RGR were found highest by applying 1.8 g USG at 45-60 and 60-75 DAT while NAR was the highest with application of 2.7g USG at 60-75 DAT and lowest one was found in control (0 g USG) at 45-60 and 60-75 DAT. The highest LAI was found by applying 1.8g USG at 15, 30, 45 and 60 DAT and the lowest one was found at 60 DAT in control and at 15, 30 and 45 DAT when 2.7g USG was applied. The highest LAI and CGR were found in older tiller seedlings (35- day old) by transplanting five tiller seedlings hill-1 fertilized with 1.8g USG whereas the highest RGR and NAR were obtained in younger tiller seedlings (25-day old) by transplanting single tiller seedling hill-1 fertilized with 1.8g USG per four hills of every alternate row.DOI: http://dx.doi.org/10.3329/pa.v24i1-2.19094 Progress. Agric. 24(1&amp;2): 17 - 27, 2013

Effects of Photoperiodism to The Growth Rate of Hibiscus sabdariffa L

Red roselle (Hibiscus saddariffa L.) is a short day plant, this plant is only cultivated in a certain time period. There is a need to manipulate the environment where this plant can grow. The objective of this research was to study the influence of day length tothe relative growth rate (RGR) of H.sabdariffaL. Day length treatment was carried out by covering plants by black cover. Day length treatments were given in 8, 9,10, 11 and 12 hours of light exposure. Parameters measured were RGR of height plant, diameter of stem, number, and color of leaves. Harvesting was carried out when the flower crown fell or petals furl (the age of plants reached 3-4 months). The result of this research showed that highest plant was obtained at 10 hours day length (128.20 cm), the largest stem diameter growth rate was obtained at 8 hours (1.79 cm), number of leaves at 10 hours (183.40),and green color of leaves on 12 hours (scale 4). The highest RGR was obtained at 8 hours for all parameters except the height of plant and the color of leaves. Plant height, diameter and number of leaves at 8,9,10, and 11 hours of day length did not show significance difference. This showed that roselle is a short day length plant that grow optimal under 12 hours of day length.