Development Of Tomato Seedlings Research Articles

Germinação e desenvolvimento de mudas do tomateiro Super Marmande submetidos à aplicação de giberelina em diferentes níveis de sombreamento

Devido à crescente importância socioeconômica do fruto do tomateiro, a preocupação acerca da germinação e do crescimento vegetativo dessa espécie é alvo de estudos para seu melhoramento, visando principalmente ao aumento da produtividade. Portanto, objetivou-se avaliar a influência do ácido giberélico e de diferentes níveis de sombreamento na germinação e no desenvolvimento inicial das mudas de tomateiro da variedade Super Marmande. O delineamento experimental foi em blocos ao acaso e os tratamentos arranjados em esquema fatorial (2x3), sendo o fator A com e sem a aplicação do hormônio, Giberelina (GA), na concentração de 200 mg.L-1, e o fator B com três diferentes níveis de intensidade luminosa (pleno sol (0%), 70 e 90% de sombreamento). A germinação e a condução do experimento foram realizadas em bandejas de polietileno com substrato comercial Terral®, composto por 20 plantas com 10 repetições cada e as avaliações foram realizadas 26 dias após a semeadura (DAS). Foram analisados taxa de germinação diária, índice de velocidade de germinação, porcentagem de germinação, massa fresca e seca da plântula inteira, volume de raiz, diâmetro do caule, comprimento de raiz e altura da parte aérea e pigmentos fotossintéticos. Os resultados demonstraram que somente os níveis de sombreamento influenciaram na germinação. Já a utilização do ácido giberélico na concentração de 200 mg.L-1, para as mudas do tomateiro Super Marmande, não apresentou efeito significativo. O desenvolvimento das mudas nos níveis de sombreamento de 70% e 90% foi melhor quando comparado com o tratamento a pleno sol.

ANTIOXIDANT POTENTIAL OF TOMATO (SOLANUM LYCOPERSICUM L.) SEEDLINGS AS AFFECTED BY THE EXOGENOUS APPLICATION OF ORGANOIODINE COMPOUNDS

Salicylic acid is one of the regulatory compounds involved in numerous processes in plants. Previous studies indicated that also its halogen derivatives may exhibit similar roles. The aim of the work was to evaluate the influence of iododerivatives of salicylic acid such as: 5-iodosalicylc acid (5I-SA) and 3,5-diiodosalicylic acid (3,5diI-SA) on selected aspects of antioxidant capacity of tomato seedlings. The efficiency of improving iodine accumulation in tomato seedlings was also studied. No tested organoiodine compound had a negative effect on the growth and development of tomato seedlings. The presence of iodosalicylic acids in the nutrient solution led to a decrease of the content of salicylic acid, ascorbic acid and phenolic compounds in tomato seedlings. A modifying effect of tested organoiodine compounds on the antioxidant activity of tomato seedling extracts varied with respect to analyzed enzyme and applied assays. It has been confirmed that higher plants can take up and accumulate iodine from organoiodine compounds in levels not causing any symptoms of toxicity.

Plant Growth Promotion Abilities of Phylogenetically Diverse Mesorhizobium Strains: Effect in the Root Colonization and Development of Tomato Seedlings.

Mesorhizobium contains species widely known as nitrogen-fixing bacteria with legumes, but their ability to promote the growth of non-legumes has been poorly studied. Here, we analyzed the production of indole acetic acid (IAA), siderophores and the solubilization of phosphate and potassium in a collection of 24 strains belonging to different Mesorhizobium species. All these strains produce IAA, 46% solubilized potassium, 33% solubilize phosphate and 17% produce siderophores. The highest production of IAA was found in the strains Mesorhizobium ciceri CCANP14 and Mesorhizobium tamadayense CCANP122, which were also able to solubilize potassium. Moreover, the strain CCANP14 showed the maximum phosphate solubilization index, and the strain CCANP122 was able to produce siderophores. These two strains were able to produce cellulases and cellulose and to originate biofilms in abiotic surfaces and tomato root surface. Tomato seedlings responded positively to the inoculation with these two strains, showing significantly higher plant growth traits than uninoculated seedlings. This is the first report about the potential of different Mesorhizobium species to promote the growth of a vegetable. Considering their use as safe for humans, animals and plants, they are an environmentally friendly alternative to chemical fertilizers for non-legume crops in the framework of sustainable agriculture.

Tomato root development and N assimilation depend on C and ABA content under different N sources

Root plasticity is controlled by hormonal homeostasis and nutrient availability. In this work, we have determined the influence of different N regimens on growth parameters and on the expression of genes involved in auxin transport and N-assimilation in tomato seedlings. NH4+ nutrition led to an inhibitory effect on root fresh weight (FW), lateral root (LR) number and root density, while an increase in the primary root (PR) length was observed. The expression of N assimilation genes GS2 and ASN1, is affected by NH4+ nutrition. Moreover, in order to relieve the toxic effect of NH4+ on root development, glucose or 2-oxoglutarate was supplied as a C source during NH4+ treatment. The addition of 2-oxoglutarate improved root parameters compared to the NH4+ regimen. N-assimilation gene analysis showed that NH4+-fed tomato plants try to alleviate the toxic effect by concurrently upregulating ASN1 and anaplerotic PEPC2 expression, whereas when 2-oxoglutarate is supplied, ASN1 induction was not observed. The addition of both C skeletons induced the expression of the ROS-scavenging genes GSH and SOD. In addition, since ABA plays a role in root development, the ABA-synthesis-defective mutant flacca was studied under NO3− and NH4+ regimens. It displayed a decrease in LR number under NO3− conditions, whereas, the NH4+-fed seedlings showed a decrease solely in PR length that was reverted when ABA was exogenously supplied. Moreover, flacca seedlings displayed a reprogramming of the N/C assimilation genes. Altogether, these results reflect the importance of N and C sources and ABA homeostasis in root development of tomato seedlings.

Pivotal roles of Tomato photoreceptor SlUVR8 in seedling development and UV-B stress tolerance

UV RESISTANCE LOCUS 8 (UVR8) is a UV-B photoreceptor that regulates various aspects of plant photomorphogenesis. Physiological functions of UVR8 have been extensively investigated in Arabidopsis. However, functions of Tomato UVR8 (SlUVR8) are largely unknown. To analyze physiological functions of SlUVR8, we generated sluvr8 knock-out mutant lines with CRISPR-CAS9 gene editing approach. At seedling stage, SlUVR8 regulates hypocotyl elongation and anthocyanin accumulation under UV-B. Moreover, SlUVR8 regulates acclimation to low dose UV-B and promotes tolerance to elevated UV-B stress. These results revealed pivotal roles of SlUVR8 in the regulation of Tomato seedling development and UV-B stress tolerance. The manipulation of photoreceptor SlUVR8 may represent a powerful tool to improve Tomato plant performance in nature where high dose UV-B is present.

Growth and development of tomato seedlings in substrates containing distinct amendments of a novel calcium montmorillonite nanocomposite hydrogel.

Several results demonstrate that the correct use of hydrogels in adequate situations can increase seedling survival rates, plant growth and water-retention capacity of the soil. A technique of producing a nanocomposite hydrogel using calcium montmorillonite (NC-MMt) was recently developed. However, research results are still necessary in order to validate this innovative hydrogel, particularly for the production of vegetable crop transplants. In this context, the main objective of the present study was to evaluate the growth and development of ‘BRS Nagai’ tomato seedlings in substrates containing different amendments of NC-MMt. The trial was conducted in a 3 x 3 factorial design, with three replications. The substrates (peat moss – T1, pine bark – T2, and coconut peat based – T3) represented the first factor and three rates of hydrogel NC-MMt (0% – R1, 1.5% – R2 and 2.0% – R3, on a w/w basis) represented the the second factor. Each plot was composed of 16 plants that were compared after three weeks in all the treatments. Root diameter (means of 2.40 mm²), number of leaves (means of 12 leaves per plant), and plant emergency percentage – PEP (means of 86.8% at seven days after sowing – DAS) did not differ significantly amongst all factors. PEP at 14 DAS, plant height, plant height/shoot dry weight ratio, root dry weight, shoot dry weight/root dry weight ratio, leaf area, and Dickinson quality index were responsive to substrates, mainly T1. Root superficial area (RSA) and root volume (RV) were significantly affected by the distinct rates of NC-MMt. Treatments R2 (1.5%) and R3 (2.0%) differ significantly compared to control – R1 (0%). Positive responses for two factors (T1 substrate; R2 and R3 NC-MMt rates) were achieved for stem diameter (SD), RSA, RV values. In addition, no phytotoxic effects were observed. Therefore, tomato seedlings of the cultivar ‘BRS Nagai’ can be efficiently produced by means of one of these combinations.

English

Yeasts are an interesting group of microorganisms, which occur naturally in soil and on plant surfaces. Few studies have analysed their potential as plant growth promoters. Thus, the aim of this study was to evaluate the indole acetic acid (IAA) production and phosphate solubilization by the yeasts Torulaspora globosa (CCA5S51 and CCA5S55), Meyerozyma guilliermondii (CCA3C98), and Rhodotorula mucilaginosa (CCA2F32), and the influence of T. globosa (CCA5S55) in the development of tomato seedlings. The results showed that T. globosa strains present both plant growth promotion traits (IAA production and phosphate solubilization). The strains of T. globosa (5S51 and 5S55) showed high IAA production (641 and 669 µg.ml-1, respectively) after 48 h of incubation, while Rh. mucilaginosa produced 406 µg.ml-1 of IAA after 120 h. The strains CCA5S55 and CCA5S51 could also solubilize 47 and 35% of tricalcium phosphate in the medium, respectively, after 12 days of incubation; whereas M. guilliermondii (CCA3C98) solubilized only 10% of the tricalcium phosphate after 12 days. The inoculation of tomato seedlings with T. globosa stimulates the plant growth; root height was statistically superior when the higher cell concentration was inoculated. The root dry weight was enhanced with addition of glucose and tryptophan. The conclusion is the yeast species T. globosa is able to produce IAA in the presence of tryptophan and also solubilize phosphate in vitro. The inoculation of tomato seedlings promoted its development. The cell concentration and the addition of glucose and tryptophan must be evaluated in details to attain optimized yields. Key words: indole acetic acid (IAA) production, phosphate solubilisation, yeast as plant growth promoter.

Pre-planting inoculation for early establishment of Dicyphus bolivari and D. errans on tomatoes

Slow establishment and risks of plant damage are major constraints for the use of the predatory mirid bugs that are commercially available for release in greenhouse crops. Therefore, a new interest has turned towards two predatory Dicyphus species (Heteroptera: Miridae) that have been investigated in the past but have not been used commercially in augmentative biological control. We assessed their development duration and survival at temperature and day length of summer and winter conditions and assessed the feasibility of pre-planting predator establishment on plant seedlings under those conditions. Dicyphus bolivari (Lindberg) and D. errans (Wolff) nymphs reached the adult stage in 47.4 (winter conditions) and 18.6 days (summer conditions) and 46.0 (winter) and 16.3 days (summer) respectively. They showed more than 90% survival when provided with food (Ephestia eggs). Provision of food allowed females to lay more eggs and to distribute them more evenly among tomato seedlings. No injuries or other negative effects on tomato seedling development were observed. Nymph development time of the two mirid species studied were slightly higher than other commercial mirid predators. The results show great potential of these predatory bugs, which are now being tested under field conditions.

Multidimensional Analysis Associated With Growth Analysis in the Selection of Organic Substrates for the Production of Tomato Seedlings

Tomato (Solanum lycopersicum L.) is a crop whose cultivation is of great importance in economic and social aspects. However, the development of efficient and low-cost technologies is essential for the growth of agricultural activity in the region. Among the most studied technologies, the production of quality seedlings in organic substrates is highlighted. In this context, the objective was to evaluate the development of tomato seedlings produced with organic substrates, using the decomposed stem of babassu palm and goat manure, using the multidimensional technique with the help of canonical functions associated with growth analysis. The treatments consisted of 25%, 50% and 75% sand aggregates, 25% to 50% sand addition, 25% to 50% sand and commercial substrate, established in a completely randomized design with 28 treatments and four replications in a 7 × 4 factorial scheme, the first factor consisting of seven substrates and the second of four evaluation periods (7, 14, 21, 28 days after emergence). Were analyzed shoot length and main root length; dry mass of the aerial part and of the root system and leaf area. These variables were analyzed through multidimensional analysis with the help of canonical functions and growth analysis. In general, the substrates consisting of goat manure and sand were superior to the substrates consisting of the decomposed palm tree stem and the commercial substrate. The alternative substrate formed by the mixture of goat manure, in the proportion of 25% of sterilized sand + 75% goat manure, constitutes the best option for the production of tomato seedlings.

Phosphorus and Zinc Extractable and Total in Substrate Enriched Coconut Powder and Tomato Cultivation

Phosphorus (P) and Zinc (Zn) stand out for their interactions, however, little is known about the interaction of these elements in organic substrates used in the development of plants. The objective of this work was to evaluate the extractable and total P and Zn of the enriched coconut powder substrate and the development of tomato seedlings grown on the same substrate. The work consisted of 10 treatments and 4 replicates with different doses of P and Zn. The substrate used was coconut powder enriched with nutrient solutions in a ratio of 10:1 (v/m). Then, the experiment was conducted using the enriched substrate to observe the effect of P and Zn doses on the development of tomato seedlings in trays. The height, number of leaves and the dry matter of the plants were evaluated. For the water and Mehlich-1 extractors the highest values of P and Zn were for treatments with the highest doses and only the quadratic positive effect of P did not differ statistically in the enriched coconut powder substrate. The results showed that the coconut powder used as substrate is deficient in P and Zn. The highest development of the seedlings was obtained at the doses of 74 mg L-1 P and 3.25 and 4.75 mg L-1 Zn of the substrate enrichment solution.

Effects of Adding Nitrogen to Vermicompost on Tomato Seedlings Under Greenhouse Conditions

ABSTRACTVermicompost, a byproduct of earthworm digestion of organic solid waste is receiving attention as a peat substitute in the production of plug seedling media. We aimed to test the effects of adding nitrogen to vermicompost on the morphological development of tomato seedlings. Nursery experiments on tomato seedlings were carried out in the greenhouse. Urea at 0.00 kg/m3, 0.25 kg/m3, 0.50 kg/m3, and 1.00 kg/m3 was added to vermicompost and to the vermicompost-vermiculite (at a volume ratio of 4:1) mixture. Results showed that (1) Nitrogen application at different rates to the vermicompost significantly increased the strong seedling index (SSI) at the middle (T1) and late (T2) seedling growth stages. Besides, nitrogen application significantly increased concentrations of available nitrogen (available-N) at the beginning of seedling cultivation (T0) and nitrate nitrogen (NO3−-N) at T2 in vermicompost. (2) Adding nitrogen to vermicompost significantly increased the number of root tips at T1 and T2 and the root volume at T2. And it significantly decreased the electrical conductivity (EC), total N (TN), available N, ammonium N (NH4+-N), and NO3−-N at T1 and T2. (3) Adding nitrogen to the vermicompost-vermiculite mixture significantly increased the root/shoot ratio, and SSI at T1 and T2. And it significantly increased the pH and reduced the EC at T1 and the available-N, NH4+-N, and NO3−-N at T2. In short, adding nitrogen (0.5～1.0 kg/m3 urea) to vermicompost improved the shoot and root morphological development of tomato seedlings, as well as the biomass accumulation and allocation. Adding nitrogen to the vermicompost-vermiculite mixture further promoted the development of tomato seedlings.

Effects of different proportions of red and blue light on the growth and photosynthesis of tomato seedlings

In order to explore the mechanism of response of growth and development of tomato seedlings to the combination of red and blue light, the light-emitting-diodes (LEDs) as precision modulation light sources were used in this study with 7 treatments including red (R) light, blue (B) light and combination of R+B light (9R1B, 6R1B, 3R1B, 1R1B, 1R3B), white (W) light as control, and the effects of different proportions of R and B light on the growth, photosynthetic pigment content, photosynthetic characteristics, chlorophyll fluorescence and root activity of tomato seedlings with variety of 'SV0313TG' as experiment material were studied. The results showed that there were significant differences in growth of tomato seedlings under treatments of different proportions of R and B light. The plant height, specific leaf area and intercellular CO2 concentration of tomato seedlings were significantly promoted by R light, while Fv/Fm and χPS2 were decreased, the root growth was inhibited as the root activity declined, so that the seedling index was reduced. The seedling growth was significantly suppressed under B light and the chlorophyll content was decreased, while the chlorophyll a/b was enhanced. Furthermore, combination of R+B light was be-neficial to the growth and development of tomato seedlings, and the plant dry mass, chlorophyll content and photosynthetic performance were significantly increased under 3R1B. In addition, seedlings grew strongly and had the highest value of seedling index under this treatment. In conclusion, the combination of R+B light could promote photosynthetic pigment content and photosynthetic efficiency in leaves of tomato seedlings, as well as plant growth, especially for treatment of 3R1B.

Germinação de sementes de tomateiro tratadas com fontes de ferro e zinco para biofortificação agronômica

O tomateiro é uma cultura muito exigente em nutrientes e possui destaque econômico em todo o mundo. No Brasil, alguns tipos de solos são deficitários em micronutrientes. Além do mais, pessoas de várias regiões do mundo têm sofrido devido aos elevados índices de desnutrição e anemia promovidos pela deficiência de ferro e zinco. Portanto, o objetivo do presente trabalho foi avaliar a germinação de sementes e desenvolvimento de plântulas de tomate submetidas às fontes de ferro e zinco, utilizando técnicas de biofortificação agronômica. O experimento foi realizado na Universidade do Estado da Bahia (UNEB), em Juazeiro-BA. O delineamento utilizado foi inteiramente casualizado, constituído de 9 tratamentos e 4 repetições de 25 sementes. Para o tratamento de sementes considerou-se uma produção média de 90 ton ha-1 e um espaçamento de 1,2 x 0,8 m entre plantas. Utilizaram-se como fonte dos nutrientes Sulfato de Ferro e o Sulfato de Zinco. Os tratamentos foram constituídos de 0, 5, 10, 15 e 20% de Zn e 0, 5, 10, 15 e 20% de Fe extraídos pela cultura até a colheita. As características avaliadas foram porcentagem e cinética de germinação, além da coleta de cinco plântulas para determinação do comprimento da parte aérea e raiz, massa fresca e seca da plântula. Os resultados apontam que o incremento de dosagens de Fe e Zn nas sementes não se mostrou positivo, reduzindo a germinação e não proporcionando um desenvolvimento de plântulas.

閉鎖型苗生産システムにおける遠赤色LED光がトマト苗の生育に及ぼす影響

明期終了時の短時間の光照射 (EOD光照射) の処理では, PSSがEOD-B区で0.56, EOD-R区で0.89およびEOD-FR区で0.13となった. PSSが最も低いEOD-FR区で茎伸長が促進され, 徒長した. 一方，第1花房着生葉位は試験区間で差がみられなかった. よって, EOD-FR処理によりトマトの避陰反応が誘導されることが示されたが, 花成は促進されなかった. 他方, 明期 (16 h) における遠赤色光量を調節した実験では, 第1花房着生葉位は試験区間で差がみられず, 低R/FR比の遠赤色光が含まれる全処理区で高R/FR比のFR0区と比べて茎伸長が促進され, 徒長した. よって, 明期 のPSSが0.72以下のFR50区、FR100区およびFR150区で避陰反応は誘導するため, 一次育苗で遠赤色光を付加する必要はないことが示唆された. 以上より, EOD-FR処理や低R/FRの条件では, 花成を促進することはなく, 茎伸長を促進するため，閉鎖型苗生産システムではこのような光環境制御は望ましくないと考えられた.

Tomato seedling development is improved by a substrate inoculated with a combination of rhizobacteria and fungi

Chile's seedling production industry has been growing for the last 10 years, and demand has actually reached 1250 million seedlings per year. This system has special relevance due to the high cost of seeds. In addition, there is an increasing demand for substituting synthetic agrochemicals. Therefore, the potential use of plant growth-promoting rhizobacteria (PGPR) in tomato production has been investigated. Before sowing, the micro-organisms provided by Biogram S.A. were inoculated into the substrate diluted in 250 mL/L unchlorinated water. The experiment was laid out in a ‘split-plot’ design with the two plant substrates as main plots and the inoculants as subplots, including six replicates per treatment. Tomato seedlings were grown using two different plant substrates: a mixture of 70% peat and 30% perlite by volume, and a substrate with 20% peat, 20% perlite and 60% compost by volume, both inoculated with Bacillus subtilis or Pseudomonas fluorescens or Bioroot®, which is a commercial product containing B. subtilis, P. fluorescens, Trichoderma harzianum, yeast, algae and Nocardia. For control, uninoculated tomato seedlings were grown on the respective plant substrates. Variance analysis did not identify significant interactions between substrate type (main plots) and inoculation treatment (subplots), P ≤ 0.05. There were significant differences between inoculants (P ≤ 0.05). Means were compared by using the Tukey's multiple range test. Tomato growth in terms of leaf area (cm2/plant) and shoot and root dry weight (g/10 plants) was improved for the seedlings grown on the substrate with 70% peat and 30% perlite, compared to the compost containing an alternative that is valid for both uninoculated perlite peat and all inoculated treatments where perlite peat was outstanding. Inoculation with Bioroot® improved the leaf area, shoot dry weight, root dry weight, radical contact area, volume of roots and root forks compared with the control without inoculation, when both plant substrates were analysed together. Thus, inoculation with Bioroot® can be recommended as an alternative to tomato seedling growers' dependence on synthetic agrochemicals.

Performances of different sources of arbuscular mycorrhiza on tomato (Lycopersicon esculentum) seedlings

An experiment on the effect of different sources of Arbuscular mycorrhiza (AM) fungi on tomato seedlings (var. Roma VF) was conducted at the Bangladesh Agricultural Research Institute, Gazipur during rabi 2007-08 and 2008-09. Eight sources of AM fungi viz., AM-01 (Jessore), AM-02 (Rahmatpur), AM-03 (Joydebpur), AM-04 (Ullapara), AM-05 (Jamalpur), AM-06 (Hathazari), AM-07 (Ishurdi), and AM-08 (Rajshahi) were studied along with a control and mixed sources on tomato seedlings. Soil based AM inoculum at the rate of 2.0 kg/m2 was used. Biomass yield of tomato (Roma VF) increased from 14.8% to 53.6% in 2007-08 and 32.1% to 58.4% in 2008-09 over control by inoculation with different sources of AM. The highest biomass yield (301 mg/seedling) of tomato (Roma VF) was observed with AM-05 (Jamalpur source), which was higher to all AM sources except AM-07 (Ishurdi source). Nutrient uptake by tomato seedlings was improved by inoculation with AM fungi. The AM fungi from all the sources appeared to be effective in enhancing the growth and development of tomato seedlings. DOI: http://dx.doi.org/10.3329/bjar.v39i1.20067 Bangladesh J. Agril. Res. 39(1): 23-31, March 2014

Effect of monochromatic UV-A LED irradiation on the growth of tomato seedlings

Effect of 376 nm UV-A LED irradiation on the growth and morphology of tomato seedlings was studied. Tomato seedlings were grown under the 658 nm red LEDs or the red LED supplemented with two irradiation levels of the UV-A. The growth and development of tomato seedlings were significantly enhanced under the red light supplemented with the UV-A. Under the UV-A treatments, the tomato seedlings became more compact, the growth of plant organs was balanced, the leaf area was increased, and the total plant fresh and dry weights were also enhanced. Our findings suggested that the 376 nm UV-A from LEDs had a beneficial effect on the growth and development of tomato seedlings as similarly to the blue light.

Metabolomics reveals organ-specific metabolic rearrangements during early tomato seedling development

Tomato seedlings (Solanum lycopersicum cv. MoneyMaker), grown under strictly controlled conditions, have been used to study alterations occurring in secondary metabolite biosynthetic pathways following developmental and environmental perturbations. Robustness and reproducibility of the system were confirmed using detailed statistical analyses of the metabolome. LCMS profiling was applied using whole germinated seeds as well as cotyledons, hypocotyls and roots from 3 to 9 days old seedlings to generate relative levels of 433 metabolites, of which 62 were annotated. Initial focus was given to the polyphenol pathway and several additional mass signals have been putatively annotated using high mass resolution fragmentation. Clear organ and developmental stage—specific differences were observed. Seeds accumulated saponin-like compounds; roots accumulated mainly alkaloids; cotyledons contained mainly glycosylated flavonols and; hypocotyls contained mainly anthocyanins. For each organ, the developmental changes in metabolite profiles were described by using linear mixed models. Across three independent experiments, 85 % of the metabolites showed similar developmental trends. This tomato seedling system has given us valuable additional insights into the complexity of seedling secondary metabolism. How metabolic profiles reflect an interplay between depletion of stored molecules and de novo synthesis and how the overall picture for this important crop plant contrasts to e.g. Arabidopsis are emphasised.

Isolation and characterization of rhizosphere bacteria for the biocontrol of the damping-off disease of tomatoes in Tunisia

Fluorescent Pseudomonas spp., isolated from tomato and pepper plants rhizosphere soil, was evaluated in vitro as a potential antagonist of fungal pathogens. Pseudomonas strains were tested against the causal agents of tomatoes damping-off (Sclerotinia sclerotiorum), root rot (Fusarium solani), and causal agents of stem canker and leaf blight (Alternaria alternata). For this purpose, dual culture antagonism assays were carried out on 25% tryptic soy agar, King B medium and potato dextrose agar to determine the effect of the strains on mycelial growth of the pathogens. In addition, strains were screened for their ability to produce exoenzymes and siderophores. All the strains significantly inhibited Alternaria alternata, particularly in 25% TSA medium. Antagonistic effect on Sclerotinia sclerotiorum and Fusarium solani was greater on King B medium. Protease was produced by 30% of the strains, but no strain produced cellulase or chitinase. Finally, the selected Pseudomonas strain, Psf5, was evaluated on tomato seedling development and as a potential candidate for controlling tomato damping-off caused by Sclerotinia sclerotiorum, under growth chamber conditions. In vivo studies resulted in significant increases in plant stand as well as in root dry weight. Psf5 was able to establish and survive in tomato plants rhizosphere after 40days following the planting of bacterized seeds.

The flavonoid pathway in tomato seedlings: transcript abundance and the modeling of metabolite dynamics.

Flavonoids are secondary metabolites present in all terrestrial plants. The flavonoid pathway has been extensively studied, and many of the involved genes and metabolites have been described in the literature. Despite this extensive knowledge, the functioning of the pathway in vivo is still poorly understood. Here, we study the flavonoid pathway using both experiments and mathematical models. We measured flavonoid metabolite dynamics in two tissues, hypocotyls and cotyledons, during tomato seedling development. Interestingly, the same backbone of interactions leads to very different accumulation patterns in the different tissues. Initially, we developed a mathematical model with constant enzyme concentrations that described the metabolic networks separately in both tissues. This model was unable to fit the measured flavonoid dynamics in the hypocotyls, even if we allowed unrealistic parameter values. This suggested us to investigate the effect of transcript abundance on flavonoid accumulation. We found that the expression of candidate flavonoid genes varies considerably with time. Variation in transcript abundance results in enzymatic variation, which could have a large effect on metabolite accumulation. Candidate transcript abundance was included in the mathematical model as representative for enzyme concentration. We fitted the resulting model to the flavonoid dynamics in the cotyledons, and tested it by applying it to the data from hypocotyls. When transcript abundance is included, we are indeed able to explain flavonoid dynamics in both tissues. Importantly, this is possible under the biologically relevant restriction that the enzymatic properties estimated by the model are conserved between the tissues.