Radicle Growth Research Articles

Effect of different concentrations of pyrethroid and organophosphorus pesticides on seedling growth of Cicer arietinum

Seed treatment with pesticides is one of the components of IPM. Pesticides, the chemical ingredients are generally used to assassinate biological entities that cause damage to cultivated crops. To maintain the quantity and quality of the plant produce, a large number of chemicals in the form of pesticides and/or fungicides are sprayed on them. Although these compounds affect the growth of seedlings and also negatively influence the growth of symbiotic bacteria and their interaction with crop plants resulting in a reduction in nitrogen fixation by plants and ultimately yield. A study on the consequences of chemical pesticides on seed germination and seedling growth of Cicer arietinum was carried out at Chhatrapati Shahu Ji Maharaj University, Kanpur, Uttar Pradesh, India in 2016. The present study was done to assess the effect of pesticides on root length, shoot length, leaf area, fresh weight, and dry weight of seedlings. The experiment was conducted by using different concentrations viz., 0% (control), 0.5%, 1%, 1.5%, 2%, 2.5%, 5%, 7.5%, and 10% of organophosphorus monocrotophos and pyrethroid pesticide deltamethrin. Observations were done on the 7th, 14th, and 21st days of radicle emergence. The study showed that both types of pesticides such as pyrethroid deltamethrin and organophosphorus monocrotophos were found to be toxic to plants in high concentrations and can be preferred in low concentrations only like 0.5%, which is less harmful to crop plants. SAARC J. Agric., 20(1): 55-65 (2022)

​Standardization of Radicle Emergence Test to Predict Seed Vigour and Field Emergence in Blackgram [Vigna mungo (L.) Hepper

Background: Blackgram is an important pulse crop grown in India. In which, prediction of planting value of seeds before sowing is important for assured yield. Standard germination test is time consuming and doesn’t always show the seed lots potential performance, especially if field conditions are not optimal. Radicle emergence test is considered as one of the important physiological vigour test. This is a quick vigour test and also determines the planting value of various seed lots under wide range of climatic conditions. Methods: The laboratory experiment was carried out at the Department of Seed Science and Technology, Tamil Nadu Agricultural University, Coimbatore during 2019-2020 to standardize the radicle emergence test to predict seed vigour and field emergence in ten different seed lots [L1 to L4: high vigour lots ( greater than 90% germination), L5 to L7: medium vigour lots (80-90% germination) and L8 to L10: low vigour lots ( less than 80% germination)] of blackgram var. VBN 6. The radicle emergence test was conducted through top of paper method adopting ISTA rules. Result: The results showed that the significant differences were observed between seed lots in terms of physiological parameters viz., speed of germination, germination percentage, root length, shoot length, dry matter production, vigour index, mean just germination time (MJGT), mean germination time (MGT), radicle emergence and field emergence and biochemical parameters viz., electrical conductivity of seed leachate and dehydrogenase enzyme activity. The results also revealed that the seed vigour can be grouped in three categories viz., high, medium and low vigour based on the relationship between MGT and field emergence. When the MGT was less than 25 hours, the seed lots which exceeds 85 per cent field emergence could be considered as high vigour; when the MGT was 25-26 hours, the seed lots with 70-85 per cent field emergence could be considered as medium vigour and when the MGT was greater than 26 hours, the seed lots with below 70 per cent field emergence which could be considered as low vigour.

Correlation and R2 analysis of radicle emergence test to predict seed vigour and field emergence in blackgram (Vigna mungo L.) seed lots

Blackgram (Vigna mungo L.) is one of the major pulse crops grown throughout India. Prediction of seed vigour and field emergence of seed before sowing is important for assured yield. A standard germination test is time-consuming and does not always show the seed lot potential performance, especially if field conditions are not optimal. There is need of advanced technology, which can give a precise result in a short period. The experiment was conducted to correlate the radicle emergence test with seed vigour parameters to predict seed vigour and planting value of 10 varying vigour lots (L1, L2, L3, L4 - high vigour lots; L5, L6, L7 - medium vigour lots; L8, L9, L10 - low vigour lots) of blackgram var. VBN 6. The study showed that all the seed vigour parameters of the blackgram were more highly correlated with the percentage of radicle emergence with 2 mm length than with 1 mm length. The correlation analysis results showed that the radicle emergence test with 2 mm radicle length at 28 hours had a highly significant negative correlation with EC (electrical conductivity) of seed leachate (-0.974**), followed by MJGT (mean just germination time) (-0.967**) and MGT (mean germination time) (-0.933**). However, it was positively correlated with field emergence (0.972**), germination (0.952**) and dehydrogenase enzyme activity (0.928**). The maximum R2 value of 0.923 was recorded in the 28-hour counting of radicle emergence with a length of 2 mm compared with the 26-hour counting of radicle emergence with a length of 1 mm (0.913). The study concluded that counting 2 mm radicle emergence at the 28th hour could be used to quickly evaluate seed vigour in field emergence in blackgram seed lots.

Cyclopeptides Natural Products as Herbicides and Inhibitors of Cyanobacteria: Synthesis of Versicotides E and F

AbstractThe first total synthesis of cyclopeptides versicotide E and F, natural products produced by marine fungus Aspergillus versicolor LZD‐14‐1, was achieved in good yield by solid phase peptide synthesis (SPPS) of their linear precursors and solution phase cyclization. All the versicotides A−F were evaluated as herbicides and inhibitors of cyanobacterial growth. Versicotides A, B, D, E and F showed a significant inhibition of Rye grass seed's radicle growth at a concentration of 67 μg/mL. Versicotides A, B and D also inhibited seed germination and leaf development. On the other hand, Versicotides D and F caused a relevant reduction on Microcystis aeruginosa population when cultures on exponential growth were incubated with 40 μg/mL solutions of these compounds. Evaluation of the concentration of microcystins after these treatments showed that versicotide D inhibited the production of microcystins in a comparable extent to the positive control, colistine. These results indicate versicotides, with versicotides D and F as top hits, could be considered as lead candidates in the development of bioherbicides able to mitigate the environmental impact that the evolution of agriculture has had on water quality.

Screening Technique Based on Seed and Early Seedling Parameters for Cold Tolerance of Selected F2-Derived F3 Rice Genotypes under Controlled Conditions

The cold tolerance studies were carried out in a bi-parental F2 population of a cross between tolerant and susceptible parents (SKUA-529 and HEERA, respectively). The purpose was to screen the individuals of a population for primary cold-tolerance-related attributes. The information generated has a direct application and use in identifying cold tolerance quantitative trait loci (QTLs) and further can be used for genotyping with an appropriate marker system. The screening was carried out on F2-derived F3 seeds and F3 plants for seedling and agronomic traits, respectively. Two tests measuring cold tolerance were conducted. In experiment I, seeds were germinated for 28 days at 13 °C and 7 days at 28 °C, and in experiment II, the seeds were germinated for 72 h at 28 °C, 96 h at 13 °C, and once more for 72 h at 28 °C. Coleoptile length, germination percentage, and radical reduction percentages were all measured in experiment I. The radicle and coleoptile regeneration in experiment II were measured after the cold period. The improvement in cold tolerance was achieved through radicle regrowth, as evidenced by the difference between the second and first measurements. The individual lines from the F2:3 population that recorded high germination (%) were #21, #13, #14, and #15. The percentage of coleoptile length (PERCOL %) was observed to be between the ranges of 23.33% to 53.00%. The reduction in coleoptile length (REDCOL %) was also obtained, and there was less reduction in #15, #16, and #14 and it had a range between 38.46% and 75%. Radicle regrowth (REDRAG) was high at 13 °C in #7, #11, #30, #35, and #36. Survival of the seedling range was between 33.33% and up to 100%, and the highest survival rate was observed in #16. The main objective of this rotation in temperature was to emulate field conditions where there has been a drop in temperature. The evaluations were done for primary cold stress tolerance traits, and it was found that most of these traits exhibited high variability. The mapping population developed may be utilized to generate a linkage map and locate QTLs for tolerance to cold stress in rice. Further, the identified donors for cold tolerance may be utilized for breeding programs aimed at the transfer of low-temperature stress tolerance into susceptible backgrounds. In general, a genotype with improved seedling germination rates, growth rates, and leaf yellowing scores; high seedling survival; lesser reduction in coleoptile length and in radicle development; and recovery following a cold shock at the seedling stage demonstrated its cold resistance. Genotypes with a low germination percentage, a greater number of days to germination, slow growth rate and higher leaf yellowing score, high reduction in coleoptile and radicle growth, and reduced seedling survival indicated cold susceptibility.

Seed Transmission of Pathogens: Non-Canonical Immune Response in Arabidopsis Germinating Seeds Compared to Early Seedlings against the Necrotrophic Fungus Alternaria brassicicola.

The transmission of seed-borne pathogens by the germinating seed is responsible for major crop diseases. The immune responses of the seed facing biotic invaders are poorly documented so far. The Arabidopsis thaliana/Alternaria brassicicola patho-system was used to describe at the transcription level the responses of germinating seeds and young seedling stages to infection by the necrotrophic fungus. RNA-seq analyses of healthy versus inoculated seeds at 3 days after sowing (DAS), stage of radicle emergence, and at 6 and 10 DAS, two stages of seedling establishment, identified thousands of differentially expressed genes by Alternaria infection. Response to hypoxia, ethylene and indole pathways were found to be induced by Alternaria in the germinating seeds. However, surprisingly, the defense responses, namely the salicylic acid (SA) pathway, the response to reactive oxygen species (ROS), the endoplasmic reticulum-associated protein degradation (ERAD) and programmed cell death, were found to be strongly induced only during the latter post-germination stages. We propose that this non-canonical immune response in early germinating seeds compared to early seedling establishment was potentially due to the seed-to-seedling transition phase. Phenotypic analyses of about 14 mutants altered in the main defense pathways illustrated these specific defense responses. The unexpected germination deficiency and insensitivity to Alternaria in the glucosinolate deficient mutants allow hypothesis of a trade-off between seed germination, necrosis induction and Alternaria transmission to the seedling. The imbalance of the SA and jasmonic acid (JA) pathways to the detriment of the JA also illustrated a non-canonical immune response at the first stages of the seedling.

Effect of dielectric barrier discharge plasma on rice (Oryza sativa L.) seed hydration and hygroscopicity

Nonthermal plasma has been explored as a green technology for improving seed wettability and crop productivity. In this investigation, we demonstrate scalable dielectric barrier discharge (DBD) plasma treatment of rice seeds at atmospheric pressure to elucidate the effect of plasma on seed hydration, hygroscopicity, and moisture content (MC). These properties are associated with seedling quality, nutrition, and shelf-life storage. The floating approach was utilized to evaluate seed wettability for a large-scale seed lot because treated seeds become superhydrophilic and sink immediately into water, whereas nontreated seeds float on the surface. We proved that a hydrophilic surface is necessary to improve water absorption, but the extent of physical etching and chemical functionalization had the greatest impact. After 5 h of imbibition, the seeds that were treated with plasma for 10 min absorbed ∼20% more water than the nontreated seeds. After plasma treatment, seed vigor increased dramatically, as evidenced by the radicle emergence times of ∼64 h for treated and ∼69 h for nontreated seeds. Furthermore, the treated seeds yielded seedlings that were ∼10% longer compared to the nontreated seeds on day 14 of germination, even after an artificial aging process. During treatment, the MC of the seed was linearly reduced due to an ionic wind with a velocity of ∼4.7 m s−1, which was generated using a localized nonuniform electric field that was applied around the seed’s surface. DBD plasma can modify seed coatings at the nanoscale level but not the availability of its primary nutrition and hygroscopicity. Although the treated seed absorbed moisture four times faster than the nontreated seed during the first 24 h of storage in a ∼99% relative humidity environment, there was no difference in MC subsequently. Thus, plasma treatment combines the advantages of efficient imbibition and vigor enhancement, and is beneficial for long-term seed preservation.

The influence of osmo-priming on germination parameters of Telfairia occidentalis Hook f. (fluted pumpkin)

Fluted pumpkin (Telfairia occidentalis Hook F.) seed germination proceeds once adequate temperature and moisture content have been reached and dormancy is broken. Seed priming is a technique in which seeds are hydrated (control hydration) and dried to their original moisture content while preventing radicle emergence. The study aims to investigate the consequence of osmo-priming on the germination parameters of fluted pumpkin (Telfairia occidentalis). Laboratory studies were carried out using 36 seeds of fluted pumpkin which was osmoprimed with NaCl (0.05, 0.1 and 1 millimolar), MgCl2 (0.05, 0.1 and 1 millimolar) and KCl (0.05, 0.1 and 1 millimolar). Data on germination percentage, growth parameters, and chlorophyll content showed a significant difference in germination percentages between osmoprimed seeds and control seeds. The time of germination in osmoprimed seeds was significantly reduced when compared with control. The germination rate index (64%) was different between controls and osmoprimed seeds with 0.05 millimolar KCl and 0.10 millimolar MgCl2 (). The growth parameters of seedlings 15 days after sowing showed significant increas in the number of leaves, number of root branches and chlorophyll content. Seed osmopriming may be a sustainable method to increase crop production in T.ccidentalis.

Study on the Preparation and Effect of Tomato Seedling Disease Biocontrol Compound Seed-Coating Agent.

Tomato damping-off and root rot are the two most common diseases of tomatoes at the seedling stage. At present, biological compound seed-coating agents are gradually replacing chemical agents in preventing and controlling plant diseases and insect pests, regulating plant growth, and ensuring crop yields. In this study, five biocontrol bacteria (Bacillus amyloliquefaciens (Ba), Bacillus subtilis (Bs wy-1), Bacillus subtilis (WXCDD105), Pseudomonas fluorescens (WXCDD51), and Bacillus velezensis (WZ-37)), with broad antibacterial spectra were mixed with auxiliary factors (inactive components of seed-coating agent) after fermentation to compound a seed-coating agent. In this study, the formula for a compound seed-coating agent was selected through orthogonal experiment. Gaseous silica was used as a thickener, and gum arabic and sodium dodecylbenzene sulfonate were used as a film-forming agent and dispersant, respectively. The mass of fumed silica, gum arabic, sodium dodecylbenzene sulfonate, and pearlescent powder was 1.3 g, 1 g, 0.05 g, and 0.5 g, respectively. Adding gibberellin can improve the ability of seed-coating agents to promote seed germination and plant growth. This showed high efficiency in preventing and controlling seedling diseases and promoting seedling growth. After 6 days of inoculation with Pythium aphanidermatum, which caused tomato damping-off disease, the seedling mortality rate was 26.7% lower than that of the sterile water control, and 20% lower than that of carbendazim. After 21 days of inoculation with Fusarium sp., which caused tomato root rot disease, the seedling mortality rate was 44.31% lower than that of the control, and 22.36% lower than that of carbendazim. The plant height, stem diameter, root length, fresh weight, and dry weight of tomato seeds treated with biological compound seed-coating agent were significantly higher than that of the control. We tested the shelf life of the biological compound seed-coating agent, and found that the effect of seed germination and radicle growth did not decrease. This research provides information on the production technology and application of biological seed-coating agents in tomato production.

Single count of radicle emergence and mean germination time estimate seed vigour of Chinese milk vetch (Astragalus sinicus)

This research explored the relationship between a single count of radicle emergence (RE) and mean germination time (MGT) with seed vigour for Chinese milk vetch (Astragalus sinicus) (CMV), a globally important legume used as a forage, green manure, and rotation crop. Fourteen seed lots of CMV were used to determine standard germination (SG), RE and MGT in the laboratory. Field experiments were conducted at two sites to measure the emergence performance including field emergence (FE), seedling dry weight (SDW) and simplified vigour index (SVI). The SG ranged from 89.0 to 95.5% and was not significantly correlated with field performance at either of two sites. However, both a single count of RE at 20 hours and MGT were highly predictive of FE, SDW and SVI at both sites (R2ranged from 0.612 to 0.897 for RE; 0.604 to 0.870 for MGT). The RE was positively related to field performance while MGT was negatively related. The seed lots with lower RE at 20 hours had lower FE and higher MGT. Overall, both RE at 20 hours and MGT are suitable indices for the vigour evaluation of CMV. However, a single count of RE is more accurate, quick and convenient.

The radicle emergence test and storage longevity of cucurbit rootstock seed lots

A study was carried out to test whether a single count of radicle emergence (RE test) would correlate with the storage potential of seed lots of cucurbit (C. maxima × C. moschata) rootstock cultivars. The RE test was performed by counting radicle emergence percentage between 26 and 100 hours of germination. Seed longevity was determined by storage at 75% relative humidity at 35°C over 100 days, with seed survival curves constructed based on normal germination percentages. Ki (estimated initial viability in probits), σ (standard deviation of the normal distribution of seed death in time) and p50 (time for viability to fall to 50%) were determined through probit analysis. Correlation analysis showed that RE counts particularly between 30 and 34 hours were highly (P < 0.01) correlated with normal germination percentage, Ki and p50. It can be concluded that RE tests can be used as an indicator of subsequent seed lot longevity in cucurbit rootstock seed cultivars.

Detection of seed vigour differences in Festuca sinensisseed lots

The selection of high vigour seeds significantly affects stand establishment and initial plant growth, particularly in harsh environments. Several tests, including standard germination (SG), seed vigour index (SVI), germination under water and temperature stress conditions, radicle emergence (RE) counts, accelerated ageing (AA) and electrical conductivity (EC), were applied to evaluate the vigour of 12 seed lots of Festuca sinensis. The SG showed that all seed lots attained high germination ranging from 86 to 96%; no significant correlation was observed between SG and seedling emergence (SE) in field experiments over two years (2020 and 2021). The RE count at 88 hours, germination (15°C and -0.2 MPa) were the most correlated with SE (r = 0.881 and 0.851, respectively, P < 0.01), followed by AA (42°C for 48 hours) and SVI (0.836 and 0.753, respectively, P < 0.01). Thus, RE counts at 88 hours, germination (15°C and -0.2 MPa), SVI and AA (42°C for 48 hours) accurately detect vigour difference of F. sinensis seed lots and provide similar data to those for SE in the field.

Seed Science and Technology. Volume 50 Issue 1 (2022)

This issue of Seed Science and Technology includes several papers in which the authors have conducted seed vigour research on species where little to no previous research has been reported. Seed vigour is an important attribute of seed quality and the ISTA Vigour Committee encourages research in seed vigour on a wide range of species. It is important within seed laboratories and the seed industry to have validated vigour tests that are simple, easy and practical, and are correlated to field performance or seed longevity. A range of seed vigour tests were explored in the papers of this issue of SST with a focus on the single count radicle emergence (RE) test and / or mean germination time (MGT) for Chinese milk vetch, Festuca sinensis, cucurbit rootstocks and dill, with practical application for each specific crop. A paper using MGT and RE to evaluate emerging technologies using plasma seed priming treatments for maize is also discussed.

Specialized Metabolites from the Allelopathic Plant Retama raetam as Potential Biopesticides.

To cope with the rising food demand, modern agriculture practices are based on the indiscriminate use of agrochemicals. Although this strategy leads to a temporary solution, it also severely damages the environment, representing a risk to human health. A sustainable alternative to agrochemicals is the use of plant metabolites and plant-based pesticides, known to have minimal environmental impact compared to synthetic pesticides. Retama raetam is a shrub growing in Algeria’s desert areas, where it is commonly used in traditional medicine because of its antiseptic and antipyretic properties. Furthermore, its allelopathic features can be exploited to effectively control phytopathogens in the agricultural field. In this study, six compounds belonging to isoflavones and flavones subgroups have been isolated from the R. raetam dichloromethane extract and identified using spectroscopic and optical methods as alpinumisoflavone, hydroxyalpinumisoflavone, laburnetin, licoflavone C, retamasin B, and ephedroidin. Their antifungal activity was evaluated against the fungal phytopathogen Stemphylium vesicarium using a growth inhibition bioassay on PDA plates. Interestingly, the flavonoid laburnetin, the most active metabolite, displayed an inhibitory activity comparable to that exerted by the synthetic fungicide pentachloronitrobenzene, in a ten-fold lower concentration. The allelopathic activity of R. raetam metabolites against parasitic weeds was also investigated using two independent parasitic weed bioassays to discover potential activities on either suicidal stimulation or radicle growth inhibition of broomrapes. In this latter bioassay, ephedroidin strongly inhibited the growth of Orobanche cumana radicles and, therefore, can be proposed as a natural herbicide.

Complex Mixture of Arvensic Acids Isolated from Convolvulus arvensis Roots Identified as Inhibitors of Radicle Growth of Broomrape Weeds

Broomrape weeds (Orobanche and Phelipanche spp.) are noxious parasites that infect crops using haustoria formed at the tip of their radicles. Dichloromethane extract obtained from the roots of Convolvulus arvensis strongly inhibits the radicle growth of broomrape weeds. A complex mixture of arvensic acids was isolated as the metabolites responsible of the inhibitory activity of C. arvensis extract against broomrape radicle growth via activity-guided fractionation and 1H NMR and ESI MS data. We showed that the exposure of broomrape seedlings to this arvensic acids mixture results in a strong phytotoxic effect on their radicles in four broomrape species infecting a wide range of crops worldwide. This discovery paves the way for the synthesis of new bioherbicides and could contribute to the development of efficient and sustainable management strategies for broomrape weeds, for which control in many crops is limited or non-existing.

Seed ecophysiology of Elephant Apple (Dillenia indica)—An important tree species of the Indomalayan realm

AbstractDillenia indica produces mucilaginous seeds embedded in hard, fibrous, megafaunal fruits, and little is known about the ecological function of mucilage in its regeneration. Using standard laboratory protocols, we investigated the role of mucilage on seed dispersal (buoyancy), chemical defense (antibiotic, antifungal, antioxidant, and allelopathic activities), and seed germination. Further, we characterized seed germination, dormancy, and storage physiology of D. indica. Results revealed that mucilage associated with seed‐coat assists seeds in floating on water for a longer duration, acts as an antimicrobial agent without hampering the overall seed germination. It was noticed that fresh mature seeds possess an underdeveloped embryo that grows within the seed before radicle emergence (a sign of morphological dormancy; MD), and seeds took ~70 days to achieve 95% germination (a sign of physiological dormancy; PD). However, the rate of germination increased when seeds were treated with gibberellin or subjected to 1‐month dry‐storage (confirmation of PD). Seeds disperse with ~12% moisture and retain high viability even after ultra‐drying over silica gel, indicating an orthodox seed storage physiology. Study concludes that mucilage plays a crucial ecophysiological function in dispersal‐defense mechanism of D. indica seeds, by enhancing seed buoyancy, helping seeds to disperse long‐distance, and protecting the seeds from soil pathogens through antimicrobial activity. Our study confirmed that seeds of D. indica possess morphophysiological dormancy (MPD), unlike the MD reported in an earlier study from North India. Possible ecophysiological function of mucilage on seed dispersal‐defense mechanism and production of morphophysiological dormant and orthodox seeds in D. indica are discussed.

Effect of Aqueous Leaf Extract of Eucalyptus globulus Labill. on Seed Germination of Chickpea

The present study has been done to investigate the effect of aqueous leaf extract of Eucalyptus globulus on seed germination and rate of radicle growth of Chickpea under laboratory conditions. The study found complete inhibition of seed germination under the treatment of concentrated raw extract (14.28gm/100 ml) and its different dilutions (viz-90%, 70%, 50%, 30% & 10%). Later, a much-diluted raw extract (5.26gm/100ml) was made with its different dilutions as above to study germinations. Later case showed a gradual inhibition in radicle growth with the increasing concentration with a correlation coefficient (r=0.72).

Selected Phenolic Acids Inhibit the Initial Growth of Ambrosia artemisiifolia L.

Simple SummaryIn the context of international commitments to reduce the environmental impact of herbicides, ecologically more favorable control method approaches must be explored. This is particularly important for allergenic Ambrosia artemisiifolia L., one of the most harmful species in the world. Secondary plant metabolites and, in particular, some phenolic compounds are known to have a strong allelopathic effect on weed growth. In this study we investigated whether phenolic acids (chlorogenic acid, caffeic acid, ferulic acid, gallic acid, protocatechuic acid, p-hydroxybenzoic acid, syringic acid, vanillic acid, and p-coumaric acid) can inhibit the early growth of A. artemisiifolia. Phenolic acids were tested at five different dose levels that were up to 16 times than those naturally occurring in plants. The results show that the suppression of the early growth of A. artemisiifolia is strongly dependent on phenolic acid and its dose. Treating seeds with ferulic acid, vanillic acid, p-coumaric acid, p-hydroxybenzoic acid, or a mixture of all phenolic acids resulted in significantly better inhibition of early growth parameters than other phenolic acids. However, none of the phenolic acids tested were effective as bioherbicides at their naturally occurring doses in plants. Therefore, selected doses of phenolic acids with significantly reduced herbicide doses should be further explored to effectively control A. artemisiifolia.This study aimed to investigate whether different doses of specific phenolic acids (chlorogenic acid, caffeic acid, ferulic acid, gallic acid, protocatechuic acid, p-hydroxybenzoic acid, syringic acid, vanillic acid, and p-coumaric acid), alone or in combination, can inhibit the early growth of the common ragweed (Ambrosia artemisiifolia L., Asterales: Asteraceae). A seed bioassay was performed in Petri dishes and placed in a climate chamber to assess the effects of five dose levels of phenolic acids to radicle and shoot length, as well seedling biomass of A. artemisiifolia. The lowest dose of phenolic acid corresponded to the natural phenolic acid concentration previously reported in dry plant tissue samples from Brassicaceae cover crop plants. Results show that the inhibition of the early growth of A. artemisiifolia depends strongly on phenolic acid. Across different treatments, high doses of phenolic acids significantly shortened shoots and radicles, as well as reduced seedling biomass. Treating seeds with ferulic acid alone, vanillic acid alone, p-hydroxybenzoic acid alone, or a mixture of all phenolic acids significantly reduced all early growth parameters. The estimated effective dose for the 50% inhibition (ED50) of radicle growth in A. artemisiifolia seedlings was 368.39 ± 59.85 × 10−8 mol with ferulic acid, 135.41 ± 17.65 × 10−8 mol with p-coumaric acid, 810.36 ± 134.15 × 10−8 mol with p-hydroxybenzoic acid, and 160.11 ± 12.30 × 10−8 mol with the combination of all phenolic acids.

Phytotoxic essential oil from black turmeric (Curcuma caesia Roxb.) rhizome: Screening, efficacy, chemical basis, uptake and mode of transport

Plant-based phytotoxins play an important role in plant-plant interaction and are of great promise for the development of bioherbicide. In this study, screening of essential oils from six different Curcuma rhizomes identified black turmeric (Curcuma caesia Roxb.) oil as an efficient growth inhibitor in wheatgrass coleoptile bioassay (IC50 57.1 µg/mL). The phytotoxic efficacy of this oil was further confirmed through the dose dependent (10.0–300.0 µg/mL) inhibition of germination, coleoptile and radicle growth of wheatgrass seeds in water medium (IC50 176.7, 90.6 and 93.0 µg/mL respectively) and the pre-germinated seeds in agar medium. Activity-guided fractionation and purification of the crude oil identified curzerenone, a major furanosesquiterpene in this oil as the most active phytotoxin (IC50 13.0 µg/mL in coleoptile bioassay; 188.3, 34.7 and 36.7 µg/mL respectively in water medium). Structure-activity relationship study indicated the importance of all the functional groups for its phytotoxicity. A significant contribution by the oxygenated monoterpenes towards oil phytotoxicity was also evidenced. Though inhibitory efficacy of the oil was comparatively weak in soil, a profound activity through aerial diffusion was observed against germination and/or growth of fresh and pre-germinated wheatgrass seeds (IC50 1.4–6.2 mg/L air). The study also confirmed the uptake of active phytotoxins with no detectable transformation by the seeds in water and their persistence in the soil for at least one and half months. Further, its applicability was demonstrated through an efficient post-emergence growth inhibition (IC50 37.0–81.4 µg/mL) of bermudagrass weed in water and agar medium.

Developing soybean seed germination: low ABA and high EXP1 gene expression promote embryonic axis growth whereas the seed coat delays radicle protrusion

AbstractSeed germination implies an expansion process restarting the growth of the embryonic axis (Ax) and which is completed by radicle emergence through the seed covering layers. In developing soybean seeds, abscisic acid in Ax (ABAa) mainly inhibits Ax growth. Additionally, the expression of the EXP1 gene at the elongation zone (EZ) was found to be involved in the promotion of mature soybean Ax growth, which increased during water incubation and which was repressed by exogenous ABA. This work aimed to evaluate (1) the ABAa and EXP1 levels at the EZ and (2) the role of the seed coat (SC) in developing soybean seed germination. Whole seeds (Se), embryos (Em) and Ax at 25–45 d after anthesis (DAA) germinated in vitro, and germination performance increased with DAA. ABAa decreased in planta from 25 DAA until its critical non-inhibitory threshold (ABAc) at around physiological maturity (45 DAA). At earlier ages, the ABAc was reached during the in vitro incubation. Concomitantly, EXP1 transcripts accumulated with age into the pool of long-lived mRNAs and were up-regulated during incubation. Additionally, isolated Ax germinated faster, took up more water and increased its water potential more rapidly during incubation than Ax in Se. Also, a lower osmotic gradient was required to germinate at 45 DAA, when ABAa was no longer inhibitory. Simultaneously, the pressure to protrude SC through the micropylar area increased from 25 to 45 DAA. These results support the role of ABAa and EXP1 in controlling Ax growth and the SC in delaying radicle protrusion.