Sown In Pots Research Articles

Effect of Water Seed Priming on Establishment of Direct Seeded Rice in Well Watered Conditions and Aerenchyma Formation under Varying Water Regimes

The application of seed hydro-priming as a tool for managing the adverse effect of flooding on seed germination and emergence in rice was studied, along with aerenchyma formation in sections of roots for comparisons between rice subjected to flooded and non-flooded conditions during establishment. Three replicates of three hydro-priming times (0, 24 and 48 h) were used on three cultivars. Seeds were germinated in a growth chamber at 25 o C, 65 % RH, or sown in pots in a controlled temperature glasshouse for the emergence and aerenchyma studies. Aerenchyma formation in root cortical tissues was determined from microscopic images of hand-cut sections at 5 and 50 mm behind the tips of 60-70 mm long nodal roots. The results showed that hydro-priming for both 24 and 48 h significantly hastened germination and emergence. Water seed-priming increased plant height from 20 mm to 40 mm 4 days after sowing. Flooding for 7 days significantly enhanced aerenchyma formation at 50 mm behind the root tips. The results showed that hydropriming for 48 h was the best seed invigoration treatment for shortening the mean emergence time. It hopefully provides seeds an opportunity to escape from the negative effect of flooding on seedling establishment.

Role of Azolla Pinnata Biofertilizer Extract in Producing Healthy Tomatoes

Well-known commercial Tomato seeds (Alisa) were obtained from a famous local store. All seeds were grouped into 7 groups (5%, 10%, 20%, 30%, 40%, 50%, and Control), which were equivalent to different Azolla biofertilizers extract. Seeds of each group were left immersed in the equivalent concentration 24 hours before sown in pots with growing media of 1 peat: 1Vermeculite at the beginning of summer season (First week of May). At the time of transplantation to the field, three pots of each group were used for seed germination test; Seeds were transplanted into the field after 6 weeks. After three days of transplantation, control solution (without Azolla biofertilizer) and different Azolla biofertilizers were foliar applied, the process was repeated every 15 days till 45 days after transplanting. Randomized Complete Block Design with three replicates was adapted. Each block consisted of two rows of 1.5m in wide and 5 m long (15 m2/plot), plant spacing was 50 cm, and each replicate has 20 plants. The suggested development approaches for the summer season were conducted all through the developing season. Vegetative growth of the tomatoes was expressed as plant height, plant length, branch flower clusters, and fruits were estimated in five plants/plot after 50 days from the date of transplanting. Tomatoes of control group and Tomatoes that showed a strong vegetative growth were used for feeding Winstar rats. All Biochemical parameters showed a highly significant difference compared to the control group.

Soaking seeds of winter rapeseed with Quizalofop-P-Ethyl alters plant growth and improves yield in a rice-rapeseed cropping system

Intercropping is an effective strategy to maximize production potential, profits, and land use efficiency. Sowing winter rapeseed in rice fields is a common cultivation technique in the Yangtze River basin in China, which is the world’s largest region for rapeseed production. However, the 10–15days crop overlap in rapeseed-rice cultivation results in low and unstable yields. In this study, we investigated, using both pot and field experiments, whether presoaking oil rape seeds with Quizalofop-p-ethyl (QPE) improved winter hardiness and yield. For the field trials, rapeseed was cultivated during two growing seasons from 2009 to 2011, in no-tillage fallow rice fields at the experimental site of Wuhan. Without QPE application, seedling quality was low for rapeseed sown in pots, and grown in shady conditions, or in the fallow rice field. Seedlings showed excessive elongation of the crown, resulting in low yields and yield-related traits at maturity. Soaking seeds in QPE improved the growth and survival of rapeseed seedlings, and improved their length, weight, and root neck diameter traits. Furthermore, the treatment decreased crown length during winter. Overall yield and related traits were enhanced by the QPE treatment. The most effective concentration of QPE was 120ppm. Storing seeds for 2–10months after soaking in QPE reduced any inhibitory effect of the treatment on germination rate and plant height. Our analyses demonstrated that treating seeds with QPE (120ppm) increased the yield of rapeseed in a rice-relay cropping system.

Stimulation of soil microbiological activity by clinoptilolite: The effect on plant growth

Zeolites can mitigate ammonium losses to the environment by taking up the ions from sources such as farmyard manure and ammonium-bearing fertilizers. This ability can improve nitrogen fertilizing practice given that ammonium ions loaded onto zeolite are available for plant uptake. The main goal of this study was to assess the influence of zeolite (clinoptilolite) and ammonia-loaded clinoptilolite on growth and yield of red clover (Trifolium pratense L.), as well as their influence on the microbial dynamics in soil. Plants sown in pots were cut four times, and dry matter yield (DM) of each harvest was weighed. The number of culturable bacteria, moulds, ammonifiers, Azotobacter sp. and actinomycetes was determined at the beginning of the experiment, and after each harvest. Two control treatments (soil without fertilizer and soil supplemented with mineral fertilizer - CAN) were included in the study. The application of ammonia-loaded clinoptilolite positively and significantly affected the microbial activity and provided higher yields (from 4.9 g/pot in ammonia-loaded clinoptilolite treatment to 4.3 g/pot in soil with zeolite treatment). Our results suggest that the addition of clinoptilolite to organic fertilizers (manure, composts) could be recommended. The increase of microbial communities’ abundances and their activity represented the key benefit from clinoptilolite application.

Monitoring of Rhizosphere Bacterial Communities in Soil with Sewage Sludge Addition Using Two Molecular Fingerprinting Methods: Do These Methods Give Similar Results?

Abstract In this study, bacterial genetic diversity from the rhizosphere of barley and wheat were studied. The plants were sown in pots with aliquot amount of 15 t/ha concentration of soil additive derived from sewage sludge and agricultural by-products represented by wastes from grain mill industry and crushed corn cobs. The plants sown in pots without the addition of soil additive represented control samples. The rhizosphere samples were collected on two dates (plant flowering and maturity) and the composition of bacterial communities were detected using two molecular fingerprinting methods – automated ribosomal intergenic spacer analysis (ARISA) and terminal restriction fragment length polymorphism (T-RFLP). Microbial biomass expressed as the amount of metagenomics DNA was higher in soils with addition of soil additive, except during maturity stage in barley rhizosphere. Nevertheless, statistically significant differences between control and sludge samples were not detected in any case. Similarly, no changes were detected in the composition of bacterial community between control and sludge samples in barley and wheat rhizosphere by using cluster analysis. Only minor temporal changes in the composition of bacterial community between flowering and maturity periods were observed. These changes were related to the samples collected in the plant maturity stage. In this stage, plants were completely mature and their impact on the rhizosphere bacterial communities in the form of root exudates was limited. Statistically significant differences between ARISA and T-RFLP methods were detected in all measured values of diversity indices. Despite these differences, both methods gave results leading to similar conclusions.

Early Summer Drought Stress During the First Growing Year Stimulates Extra Shoot Growth in Oak Seedlings (Quercus petraea).

More severe summer droughts are predicted for mid-latitudes in Europe. To evaluate the impact on forest ecosystems and more specifically on forest regeneration, we studied the response to summer drought in oak seedlings (Quercus petraea). Acorns were collected from different mother trees in three stands in Belgium, sown in pots and grown in non-heated greenhouse conditions. We imposed drought on the seedlings in early summer by first watering the pots to saturation and then stopping any watering. Weight of the pots and stomatal conductance were regularly measured. Re-watering followed this drought period of 5 weeks. Height of the seedlings and apical bud development were observed. Stomatal resistance increased toward the end of the experiment in the drought-treated group and was restored after re-watering. The seedlings from the drought treatment displayed a higher probability to produce additional shoot growth after re-watering (p ≤ 0.05). A higher competition for water (two plants per pot) increased this chance. Although this chance was also higher for smaller seedlings, the actual length of the extra growth after re-watering was higher for larger seedlings (p ≤ 0.01). Both in the drought-treated and in the control group the autochthonous provenance growing on a xeric site produced less extra shoots compared to the two other provenances. Finally, stressed plants showed less developed apical buds compared to the control group after re-watering, suggesting a phenological effect on the growth cycle of oaks (p ≤ 0.0001). The higher chance for an extra shoot growth after the drought period can be considered as a compensation for the induced growth arrest during the drought period.

Pretreatment with nitric oxide reduces lead toxicity in cowpea (Vigna unguiculata [L.] walp.)

Lead (Pb) is one of the most important toxic heavy metals that reduce plant growth and development. Therefore, finding compounds that can alleviate the toxic effects of Pb is necessary. Nitric oxide (NO) is a signaling molecule that plays important roles in different physiological processes in plants, such as the response to biotic and abiotic stresses. A pot experiment was conducted to study the effects of exogenously applied NO on Pb stress tolerance in cowpea. Seeds were soaked at various concentrations of sodium nitroprusside (SNP; NO donor) (0, 0.5 and 1 mM) for 20 h, and then sown in pots containing 0 or 200 mg kg-1 Pb (NO3)2. The obtained results showed that Pb stress significantly reduced the chlorophyll value, relative water content (RWC) and net photosynthetic rate, but increased lipid peroxidation, proline content and superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) activities. Nonetheless, different levels of NO significantly lowered Pb toxicity by further increasing SOD, CAT, APX and GR activities as well as proline accumulation. NO pretreatment also raised the chlorophyll value, RWC and net photosynthetic rate but reduced lipid peroxidation. Both NO levels (0.5 and 1 mM) were effective in Pb stress tolerance; however, 0.5 mM was more effective. These results indicate that NO pretreatment plays an important role in protecting cowpea plants against Pb toxicity by enhancing antioxidant enzyme activities and proline accumulation.

Responses of seed priming with gibberellic acid on yield and oil quality of sunflower(Helianthus annusL.)

Surface sterilized seeds sunflower (Helianthus annus L.) were soaked in 0, 10−7, 10−5 and 10−3M aqueous solution of gibberellic acid (GA) for 4, 8, 12 and 16 hours (h) and sown in pots filled with 5 kg homogenous mixture of soil and farmyard manure in the ratio of 4:1. The plants were sampled at harvest for analysis of head diameter, seeds per head, 1000-seed weight, seed yield per plant, biological yield per plant, harvest index (HI), oil content and oil yield per plant, acid value, iodine value and saponification value at harvest. All attributes were found to be significantly enhanced by the GA seed priming with maximum stimulation followed by a 8 h soaking treatment with 10−5MGA. Moreover, the most of the attributes were stimulated by 70%, 123.49%, 44.76%, 41.38% and 14.93%, 63.34%, 111.76% and 1.64% over the control except the 1000-seed weight, biological yield per plant and iodine value.

English

Mungbean (Vigna radiata L.) is capable of fixing atmospheric nitrogen through bacteria living in its root nodules. To study the influence of phosphorus (P) fertilization and Rhizobium inoculation on the nodulation, growth and yield of mungbean (Vigna radiata), a pot experiment was conducted in wire house, during spring season of 2010 at University of Agriculture, Faisalabad. A composite soil sample was collected from the research area and analysis of physical and chemical properties of the soil was done. Seeds of mungbean cv, NM-92 were inoculated with Rhizobium and sown in pots containing 14 kg soil. Phosphorus was applied at 1.2, 2.4 and 3.6 g per 14 kg soil in each pot alone and along with inoculation of Rhizobium phaseoli except in control pot. The source of P was single super phosphate that was mixed with soil before filling the pots.  It was noted that combined use of P and inoculant enhanced the number of nodules per plant. The maximum nodules, 8.67 per plant, were recorded where 3.6 g P along with Rhizobium inoculation was applied. Phosphorus application along with Rhizobium inoculation increased the plant height significantly (13.2%) over control. Maximum increase in plant height at maturity, total number of pods and number of grains per pod were also recorded where 3.6 g of phosphorus along with Rhizobium inoculation was applied.   Key words: Mungbean, growth, nodulation, phosphorus, inoculation.

Desempenho de sementes de soja sob deficiência hídrica: rendimento e qualidade fisiológica da geração F1

O vigor das sementes interfere significativamente na tolerância à deficiência hídrica e no rendimento de sementes. Assim, o objetivo no presente trabalho foi avaliar a influência da deficiência hídrica sobre o rendimento e a qualidade fisiológica das sementes de soja produzidas na geração F1. O trabalho foi desenvolvido utilizando-se sementes de soja da cultivar M-SOY 8008 RR, semeadas em vasos com capacidade de 15 kg de solo, coletado do horizonte A1 de um Planossolo Háplico Eutrófico solódico, em casa de vegetação. O delineamento experimental foi inteiramente casualizado, em esquema fatorial 2x2, sendo os fatores sem e com deficiência hídrica do 1° ao 10° dia após a emergência e nível de vigor das sementes (alto e baixo), totalizando quatro tratamentos, com cinco repetições. As variáveis analisadas foram a fitomassa seca da parte aérea e a área foliar aos 10, 20, 30 e 40 dias após a emergência, rendimento e qualidade fisiológica através dos testes de germinação, primeira contagem de germinação, envelhecimento acelerado e massa de mil sementes na geração F1. A utilização de sementes de alto vigor proporciona acréscimos superiores a 15% no rendimento, em relação ao uso das sementes de baixo vigor. A deficiência hídrica do 1° ao 10° dia após a emergência não interfere no rendimento e na qualidade fisiológica de sementes da geração F1, tanto daquelas de alto como de baixo vigor.

Competitive Strategies and Growth of NeighbouringBromus valdivianusPhil. andLolium perenneL. Plants Under Water Restriction

AbstractOften perennial pastures have to tolerate soil water restriction during summer, which can affect the relative abundance of the most desired species. In the south of Chile,Bromus valdivianusandLolium perenneare preferred species. The competitiveness ofB. valdivianusandL. perennewas evaluated when sown in pots in a glasshouse as monocultures or a mix (50/50 %) with restricted water availability. The water restriction treatments were as follows: 80–85 % field capacity (FC), 45–50 %FCand 20–25 %FC, maintained for 1196 growing degree days. For both species, dry matter (DM) accumulated per plant and per pot decreased similarly with increasing water restriction, but at tiller level, resource allocation differed, forB. valdivianusroot growth was accentuated over aerial development, but this was less so forL. perenne. The foliage mass per tiller forB. valdivianusdecreased relatively more than that forL. perennewith increasing water restriction. As monocultures,B. valdivianusproduced larger tillers thanL. perenne, such thatB. valdivianustillers had 2.2 times greater lamina mass, 3.6 times more leaf area and 2.5 times greater root mass than those ofL. perenne. However,L. perenneproduced a larger number of smaller tillers that enabled foliage, root and total mass at plant level, to be similar to that ofB. valdivianus. Within the mixed pasture,L. perennetiller density increased compared with when grown as a monoculture, but not forB. valdivianus. The results of the study suggested thatL. perenneandB. valdivianushave differences in growth strategies that allow them to survive under environmental stress and competition. Competitiveness increased forL. perenneaboveground without water restriction and that forB. valdivianusincreased belowground as water restriction was increased.

Seed priming with chitosan improves the germination and growth performance of ajowan

Background: Chitosan is a polysaccharide biopolymer derived from chitin. It not only stimulates growth and increases the crop yields but also alleviates the harmful effect of abiotic stress on plant growth. The objective of this study was to investigate the effects of chitosan on germination and growth of ajowan {Carum copticum) under salt stress. This study was conducted in a laboratory and greenhouse. Material and Methods: In the first experiment seed germination of ajowan monitored under seed pre-treated by soaking in chitosan solutions of 0, 0.01%, 0.05%, 0.1%, 0.2% and 0.5% for 3 h. In second experiment, seeds soaked in chitosan solutions (0 and 0.2%) and sown in pots at different salinity levels (0, 4, 8 and 12 dS/m). Results: Results indicated that all of chitosan concentrations increased germination percentage, germination rate, seedling vigour index, length and dry weight of hypocotyl and radicle compared to control although, 0.2% chitosan concentration was more effective than other treatments. Salinity caused a significant reduction in germination percentage, shoot length, root length, shoot and root dry weight and relative water content, while chitosan adjusted the salt toxicity. Conclusions: It is concluded that chitosan would be able to stimulate germination and growth of ajowan. It is also resulted that soaking ajowan seeds with chitosan, may alleviate the inhibitory effect of salt stress on the plant growth.

The effect of temperature treatments during ‘Wielkopolski’ sunflower seed imbibition and storage on plant tolerance to chilling

Abstract The aim of the present study was to evaluate the effect of short-term high or low temperature treatments applied during seed imbibition on plant tolerance to chilling. Chilling tolerance was also investigated on seedlings obtained from dry seeds stored at low temperatures. Sunflower seeds (Helianthus annuus L. ‘Wielkopolski’) were stored at 5°C or 25°C and then subjected to low (2.5°C and 5°C) or high (35°C and 45°C) temperatures for two hours during imbibition. They were subsequently exposed to chilling (2.5°C) for three weeks. Afterwards, the seeds were transferred to 25°C for chilling injury evaluation or sown in pots and grown in the field for further growth investigation. The obtained results indicate that the sunflower seedlings, obtained from dry seeds stored at 25°C, were chilling sensitive to an exposure of 2.5°C for three weeks, which was manifested by slow root elongation, external root discoloration and a long Mean Emergence Time (MET). The storage of dry seeds at 5°C reduced seedling injuries exhibited by external root discoloration and increased chlorophyll content in leaves. Short-term (two-hour) low (2.5 and 5°C) or high (35 and 40°C) temperature treatments applied to the moistened seeds alleviated chilling effects, stimulating root elongation, limiting external root discoloration and shortening MET, accelerating plant flowering and seed maturation time, increasing the diameter and weight of the anthocarp as well as seed yield and chlorophyll content. The positive response of these methods in respect to an increase in sunflower plant tolerance to chilling indicates a possibility of their application in practice.

Time of emergence of Rumex crispus L. as affected by dispersal time, soil cover, and mechanical disturbance

Emergence pattern of the perennial weed species Rumex crispus L. was studied under semi-field conditions. Seeds from three populations were harvested from the mother plants and sown in pots buried in an experimental field, either in late autumn or after winter storage at outdoor temperatures. Seeds were sown on the soil surface or covered by a 2-cm soil layer. In addition, some of the seeds sown in autumn were also subjected to mechanical disturbance in autumn or in spring. Population and soil cover both had a strong effect on total emergence. The light requirement of the species for germination was indicated by a higher rate of emergence from seeds sown on the soil surface than from covered seeds. Sowing date influenced the timing of emergence but not the total emergence. Autumn sowing led to earlier and more concentrated emergence, while seedlings from spring-sown seeds showed a more intermittent emergence pattern. Stirring after sowing had a positive effect on emergence compared with emergence from undisturbed, covered seeds. In all populations and treatments, emergence continued throughout the growing season, contradicting earlier findings that R. crispus seeds germinate mainly in early spring and autumn, and enter secondary dormancy during summer. The delay of emergence in seeds that had remained on the mother plant over winter indicates a certain level of dormancy, which was gradually broken in early summer.

Different applications effect of Atonik growth regulator on growth and yield of cotton

The pots study was conducted during summer season of 2005 at the Field of Agriculture College - Sulaimani University to compare the influence of different application durations of growth regulator (Atonik) on two varieties of cotton (Lachata & Gedera236) which sown in pots in factorial experiment using CRD design with three replications. The result indicated that Gedera236 was surpassed significantly on Lachata variety in plant height and leaf area, While Lachata was gave a less number of non opened bolls with significant differences and there was no significant differences among the two varieties for the remainder characters. Significant differences were observed for the different durations of growth regulator application. Atonik application treats (after one month of Germination, at 10% flowering and at boll set stage) were surpassed the control and seed embedded treat in Atonik for 24 hrs. in most studied characters. There was Significant interaction between varieties and Atonik application duration treats, Gedera236 at boll set stage was found to be superior in plant height, for the other characters (No. of fruit, branches, opened boll No., leaf area, chlorophyll percent, seed cotton yield and lint cotton, cotton yield and seed weight) Lachata has registered the highest mean value at boll set stage application. For ginning outturn the highest values was registered for Gedera236 during the application of Atonik at the beginning of flowering stage.

Effects of temperature, light, storage conditions, sowing time, and burial depth on the seed germination of Cardiocrinum cordatum var. glehnii (Liliaceae)

In this study, we conducted experiments to accumulate practical information on the propagation and establishment of a population of Cardiocrinum cordatum var. glehnii by seed sowing. C. cordatum var. glehnii seeds require approximately 19 months from seed dispersal to cotyledon emergence in the field. However, the period from seed dispersal to radicle emergence was shortened to approximately 7–8 months by the temperature transition of 25/15°C (60 days) → 15/5°C (30 days) → 0°C (120 days) → 15/5°C (i.e., 15/5°C represents alternating temperature treatment wherein the seeds were placed at 15°C for 12 h during the day and then at 5°C for 12 h during the night). More than 90% of the seeds, which were stored dry at 5°C for 12 months and sown in pots in the field, showed cotyledon emergence, whereas in seeds stored dry at 25°C, dry at room temperature, and non-dry at room temperature, cotyledon emergence was decreased by less than 1%. More than 88% of the seeds that were stored dry at 5°C and sown in the field in October 2002 immediately after collecting, November, and from April to July 2003 showed cotyledon emergence in spring 2004. However, seeds sown in August, September, and October 2003 showed cotyledon emergences of 57.6%, 0%, and 0% in spring 2004, respectively. Seeds collected in October 2002 and sown until July 2003 in the field received adequate high temperature in summer, moderate temperature in autumn, and cold temperature in winter; therefore, the percentage of cotyledon emergence was high in spring 2004. On the other hand, seeds sown in August 2003 or later could not receive enough high temperature; thus, cotyledons emerged from only a few seeds.

Azospillum-lnoculated Maize Plant Responses to Irrigation Restraints Imposed During Flowering

Drought during flowering negatively affects both leaf physiology and grain yield in maize (Zea mays L). We found that Azospirillum brasilense BR11005 could ameliorate these effects. Hybrid DK 636 seeds were inoculated with either autoclaved (control) or living bacteria and sown in pots buried in the field. During flowering, irrigation treatments were: high (HM), medium (MM), and low (LM), corresponding to 100%, 50%, and 25% of the evapotranspirative demand, respectively. Water potential (Ψ), water content (WC), stomatal resistance, chlorophyll content, photosynthetic rate, and proline concentration were determined during the stress period. At harvest, grain number, grain weight (GW, mg grain - 1 ), grain yield (g plant - 1 ), and harvest index (HI), were determined. After LM treatment, plants had increased stomatal resistance, and also showed pronounced reduction in Ψ, WC and chlorophyll content. These effects were weaker in plants previously inoculated with living bacteria, where a significantly higher leaf proline concentration was also evident. Moreover, GW and HI drop due to water restriction during flowering was more pronounced in controls. In short, the physiological improvement of maize plants due to Azospirillum inoculation, could account for the amelioration of the harmful effects that a water shortfall during the flowering period could cause on grain production.

Effect of Temperature at the Ripening Period on Dark Respiration and Dry Matter Production in Rice.-Comparison of the effects in the plants sown in pots at different times-

登熟期の気温の違いがポット栽培したイネ個体の暗呼吸量と穂の乾物成長に及ぼす影響を定量的に検討するため, 4月, 5月, 6月の3時期に播種することで登熟期の気温を変え, 気温の差が登熟期の暗呼吸速度と乾物生産に及ぼす影響を調査した. 出穂日は4月播種では8月4日で, 5月と6月播種ではそれぞれ4月播種より14日と28日遅かった. 4月播種における出穂後6日目∼19日目の平均気温は, 5月と6月播種より約4°C高かった. 回帰法により成長呼吸と維持呼吸を推定すると, 穂の暗呼吸速度は主に穂の成長に関わっており, 穂の維持呼吸は4月播種と5月播種では高く, 6月播種で低かった. 茎葉部の暗呼吸速度は主に穂への炭水化物の転流に関わっており, 茎葉部の維持呼吸は4月播種と5月播種で高く, 6月播種で低いと推定された. つまり, 出穂期の違いによる平均気温の上昇は必ずしも維持呼吸を増大させないことが示唆され, 維持呼吸は登熟期の気温に直接影響されるだけでなく, それまでの生育前歴によっても変わると考えられた. また, 穂の乾物成長は維持呼吸の増加にともなう暗呼吸量の増大によって低下することが定量的に示された.

Evaluation of the Endophyte Enterobacter cloacae SM10 Isolated from Spinach Roots for Biological Control against Fusarium Wilt of Spinach

Six hundred sixty-three isolates of microorganisms, including fungi and bacteria, were collected from surface-sterilized roots of spinach (Spinacia oleracea L.) growing in commercial greenhouses in Kyoto Prefecture. These isolates were screened for their ability to control Fusarium wilt of spinach caused by Fusarium oxysporum f. sp. spinaciae. In primary screening, spinach seeds were treated with the isolates, sown in pots containing sterilized soil, and then challenge-inoculated with the pathogen. Nine bacteria were effective in reducing disease incidence. Subsequently, spinach seeds were treated with the selected isolates, then sown in an infested field and grown from June to July 1998. Four bacteria reduced disease incidence. One of these four, designated as SM10, significantly suppressed the disease. Based on bacteriological properties, SM10 was identified as a strain of Enterobacter cloacae. SM10 was observed within xylem vessels of spinach roots using light and immunoelectron microscopy, indicating E. cloacae SM10 was an endophytic bacterium of spinach.

Leaf photosynthetic characteristics of beech (Fagus sylvatica) saplings during three years of exposure to elevated CO(2) concentration.

Beech (Fagus sylvatica L.) seedlings were cultivated from seeds sown in pots or directly in the ground in outdoor chambers that were transparent to solar radiation, and provided either ambient air or CO(2)-enriched air (ambient + 350 &mgr;mol mol(-1)). The rooting volume was high in all experiments. In the short-term experiment, potted plants were assigned to a factorial CO(2) x nutrient treatment (optimal nutrient supply and severe nutrient shortage) for 1 year. In the long-term experiment, plants were grown directly in the ground and received an optimal supply of water and nutrients in both CO(2) treatments for 3 years. Nutrient stress caused carboxylation capacity (V(m)) to decrease in the potted seedlings exposed to CO(2)-enriched air during their first growing season. In the long-term experiment with optimal nutrient supply, CO(2)-enriched air did not affect V(m), but caused an upward acclimation of maximum electron transport rate (J(m)). Consequently, there was a 14% increase in the J(m)/V(m) ratio, indicating nitrogen reallocation to maintain an equilibrium between RuBP consumption and RuBP regeneration. Both V(m) and J(m) decreased during the growing season in both CO(2) treatments. Although upward acclimation of J(m) was no longer apparent at the end of the third growing season, plants in CO(2)-enriched air maintained a higher J(m)/V(m) ratio than plants in ambient air, indicating that photosynthetic acclimation always occurred. Second flush leaves appeared during each growing season. When expressed on the basis of foliar nitrogen concentration, their photosynthetic characteristics (V(m) and J(m)) were enhanced compared with other leaves. Because the number of second flush leaves was also increased in the elevated CO(2) treatment, this response should be taken into account when modeling the effects of elevated CO(2) concentration on canopy photosynthesis. Stomatal conductance decreased in response to atmospheric CO(2) enrichment; however, the stomatal response to irradiance followed a single relationship based on two stomatal conductance models.