Poor Seedling Establishment Research Articles

Detection and characterization of quantitative trait loci for coleoptile elongation under anaerobic conditions in rice

ABSTRACT Low oxygen concentrations in flooded paddy fields cause poor seedling establishment in wet direct seeded rice. We aimed to identify novel genomic regions associated with coleoptile elongation under anaerobic conditions in order to improve seedling establishment. Chromosome segment substitution lines (CSSLs), substituted with Koshihikari (Japonica-type) in the IR 64 genetic background (Indica-type) were evaluated. These lines were imbibed with a hydroponic solution containing Oxyrase to create a stable anaerobic condition and coleoptile lengths were measured six days after incubation at 30°C. Among the CSSLs, only SL2111 had a significantly longer coleoptile (23.9 mm) than that of IR 64 (14.3 mm). From genotype and phenotype analyses, a novel QTL, referred to as qACE3.1, for coleoptile elongation under anaerobic conditions was detected on chromosome 3. To explore the molecular mechanism of qACE3.1, the expression levels of genes encoding enzymes involved in starch degradation and fermentation were assessed. In SL2111 coleoptiles, the expression levels of pyruvate decarboxylase were significantly higher than in IR 64 coleoptiles whereas those of alcohol dehydrogenase were lower. In contrast, no differences were observed in the expression levels of genes associated with starch degradation. These results imply that qACE3.1 may specifically affect fermentative metabolism. In addition, we evaluated the impact of qACE3.1 on seedling establishment under flooded conditions in a paddy field.

Germination Syndromes and Their Relevance to Rangeland Seeding Strategies in the Intermountain Western United States

Rangelands in the western United States exhibit extremely high temporal variability in seedbed microclimate, and this variability contributes to poor establishment of revegetation species that are typically planted in the fall. We conducted long-term simulations of cumulative germination as a function of planting date and identified alternative germination syndromes based on population-level responses to environmental variability. These germination syndromes reveal ecologically significant differences but also noteworthy similarities in species and seed lot response that can inform rangeland restoration planning and management. Seed germination may occur much sooner than assumed under the traditional paradigm of fall-planting/spring-emergence in the intermountain western United States, and seed germination per se does not appear to be a bottleneck for successful establishment in most years. Instead, simulations of germination response support recent hypotheses that postgermination/preemergent mortality may be the larger contributor to poor seedling establishment. Our data support two general strategies to improve the likelihood of seedling survival into the spring: seeding as late as possible in the fall and active diversification of germination syndromes within a given seed mix. Consistent application of these strategies could increase the probability that some seeds are always available to take advantage of any pulse of seedbed favorability in the late fall, winter, or early spring.

Differences in leaf physiology among juvenile pines and oaks following high-severity wildfire in an Arizona Sky Island Mountain range

Recent increases in wildfire severity are converting pine-oak (Pinus-Quercus) woodland to oak shrubland in many sites in the southwestern United States. A key mechanism underlying this transition is the vigorous resprouting capacity of oaks compared to low regeneration rates in pines following wildfire. Differences among species in leaf physiological characteristics may also contribute to such vegetation type conversions, especially in the context of recent increased regional aridity. To that end, we evaluated variation in leaf functional traits in post-fire recruits five years after the 2011 Horseshoe Two in the Chiricahua Mountains, Arizona, USA. We measured a suite of functional traits in two pines (Pinus engelmannii and P. leiophylla) and two oaks (Quercus hypoleucoides and Q. arizonica), including leaf gas exchange, leaf pigment concentrations, leaf spectral reflectance, and wood xylem δ13C, δ18O isotopes, and integrated water use efficiency (iWUE). The four study species displayed a range of plant functional traits tied to desiccation tolerance. P. engelmannii seedling recruits presented invariably low maximum photosynthetic rate (Amax), stomatal conductance (gs), and transpiration (E), and high relative leaf water content during the peak of the May-June drought, a response strongly indicative of a desiccation-avoidant leaf that prioritizes water conservation over carbon fixation in arid conditions. In contrast, resprouts of both oaks displayed leaf desiccation tolerance, with high levels of gs and E and low relative leaf water content. Gas exchange in P. leiophylla resprouts was more similar to the oaks, except for relative water content, which was similar to that of P. engelmannii. Compared to the other two species, P. engelmannii and Q. hypoleucoides exhibited significantly higher δ13C, δ18O and iWUE values—a pattern that appears to have arisen from different mechanisms in the two species. In desiccation-avoidant P. engelmannii, low instantaneous gs and high δ18O suggested that low stomatal conductance rather than high photosynthetic rates led to high iWUE, whereas lower δ18O and very high pigment concentrations in Q. hypoleucoides suggest a more important role for Amax in this species. Neither fire severity nor physiography influenced the physiological responses in any of the four species, suggesting that the expression of resprout and seedling functional traits is fixed. These results raise the possibility that differences in leaf physiological characteristics contribute to the regeneration success of some oak species and the poor seedling establishment of obligate seeder pines, such as P. engelmannii, after high-severity wildfire in the American Southwest.

Mesocotyl elongation, an essential trait for dry-seeded rice (Oryza sativa L.): a review of physiological and genetic basis.

(1) Mesocotyl elongation is responsive to abiotic stresses, such as deep sowing drought, submergence, chilling, and salinity. (2) Humus soil culture with a burial depth of 6cm and at the temperature of 30°C could be the optimum method for mesocotyl length phenotyping, The frequently colocalized quantitative trait loci (QTL) controlling mesocotyl elongation were located on chromosome (3) 1 (RM562-RG146), chromosome 2 (RZ288-RM145), and chromosome 3 (RM426-RM520). Dry direct-seeding is becoming a popular rice cultivation technology in many countries, which reduces water use and labor costs enormously. Meanwhile, direct-seeding rice is also facing the problems of low seedling emergence rate, poor seedling establishment, weed infestation, and high crop lodging rate. To take the full advantages of direct-seeding, both agronomic and genetic solutions are needed. Varieties with optimum mesocotyl length are desired for improving rice seedling emergence rate, particularly under deep sowing and submergence, which is adopted to reduce lodging and increase tolerance to abiotic stresses. In this review, we summarized the physiological and genetic mechanisms of mesocotyl elongation in rice. The elongation of mesocotyl is affected by light, temperature, and water, and, as a result, is responsive to sowing depth, water content, and soil salinity. Plant hormones such as abscisic acid (ABA), brassinosteroid (BR), strigolactones (SLs), cytokinin (CTK), ethylene (ETH), jasmonic acid (JA), gibberellin (GA), and indole-3-acetic acid (IAA) play important roles in regulating mesocotyl elongation. A humus soil culture protocol developed by our team was shown to be a better high-throughput method for measuring mesocotyl length in large scale. Sixty-seven QTL controlling mesocotyl length were reported, which are distributed on all the 12 chromosomes. Twelve chromosomal regions were repeatedly found to have QTL using various mapping populations and methods. These regions should be targeted in future studies to isolate genes and develop markers for molecular breeding. Two genes with very different molecular functions have been cloned, highlighting the genetic complexity of mesocotyl elongation.

Impact of priming on seed germination, seedling growth and gene expression in common vetch under salinity stress

Salinity is one of the most important abiotic stress factors that is expanding its influence because of global climate change and global warming. It causes gene expression changes, a reduction in seed germination and related characteristics, and poor seedling establishment in many crop plants by creating a lower osmotic potential in the seedbed and/or toxic ion effects in germinated seeds. In recent years, seed priming has been considered a promising strategy in modern stress management to protect plants against stress conditions. This study was conducted to elucidate the effects of osmopriming with polyethylene glycol 6000 (PEG-6000) on seed germination, seedling growth and gene expression in the common vetch (Vicia sativa L.) in different saline conditions. Common vetch seeds were primed with PEG-6000 solutions having different osmotic potentials (0.00, -0.50, -0.75, -1.00, -1.25, and -1.50 MPa) for 12 hours. Control (un-primed) and primed seeds were germinated and seedlings were grown in different saline conditions (EC= zero, 4, 8 and 16 dS m-1). Furthermore, gene expression was compared in the primed seedlings in two different osmotic potentials (0.00 and -1.50 MPa) by microarray technology. Results demonstrated that germination percentage of common vetch seeds and seedling growth were diminished by high salinity. However, several priming treatments alleviated the adverse effects of high salinity on germination and early seedling growth of common vetch. The microarray showed that the expression of many genes in both stress and normal conditions was not significantly different.

Tri-Hydroxy-Triacylglycerol Is Efficiently Produced by Position-Specific Castor Acyltransferases.

Understanding the biochemistry of triacylglycerol (TAG) assembly is critical in tailoring seed oils to produce high-value products. Hydroxy-fatty acid (HFA) is one such valuable modified fatty acid, which can be produced at low levels in Arabidopsis (Arabidopsis thaliana) seed through transgenic expression of the castor (Ricinus communis) hydroxylase. The resulting plants have low seed oil content and poor seedling establishment, indicating that Arabidopsis lacks efficient metabolic networks for biosynthesis and catabolism of hydroxy-containing TAG. To improve utilization of such substrates, we expressed three castor acyltransferase enzymes that incorporate HFA at each stereochemical position during TAG synthesis. This produced abundant tri-HFA TAG and concentrated 44% of seed HFA moieties into this one TAG species. Ricinoleic acid was more abundant than any other fatty acid in these seeds, which had 3-fold more HFA by weight than that in seeds following simple hydroxylase expression, the highest yet measured in a nonnative plant. Efficient utilization of hydroxy-containing lipid substrates increased the rate of TAG synthesis 2-fold, leading to complete relief of the low-oil phenotype. Partition of HFA into specific TAG molecules increased the storage lipid available for mobilization during seedling development, resulting in a 1.9-fold increase in seedling establishment. Expression of a complete acyltransferase pathway to efficiently process HFA establishes a benchmark in the quest to successfully produce modified oils in plants.

Mapping of dwarfing gene Rht14 in durum wheat and its effect on seedling vigor, internode length and plant height

Short coleoptiles associated with GA-insensitive Rht-1 alleles in wheat reduces yield due to poor seedling establishment under dry, or stubble-retained conditions. Hence there is a need for alternative dwarfing genes for wheat improvement programs. GA-sensitive dwarfing gene Rht14 confers semidwarf stature in wheat while retaining longer coleoptiles and early seedling vigor. Two RIL populations were used to identify the map position of Rht14 and to estimate its effect on plant height, coleoptile length, seedling shoot length, spike length and internode length. Rht14 on chromosome 6A was mapped in the genomic region 383–422 Mbp flanked by GA2oxA9 and wmc753 in a Bijaga Yellow/Castelporziano RIL population. Recombination events between Rht14 and GA2oxA9 in the RIL population indicated that Rht14 might not be allelic to GA2oxA9. The conserved DNA sequence of GA2oxA9 and its flanking region in Castelporziano also suggested that the point of mutation responsible for the Rht14 allele must be a few Mbp away from GA2oxA9. The dwarfing effects of Rht14 on plant height, internode length and seedling vigor were compared with those of Rht-B1b in an HI 8498/Castelporziano RIL population. Both genes significantly reduced plant height and internode length. Rht-B1b conferred a significant reduction in coleoptile length and seedling shoot length, whereas Rht14 reduced plant height, but not coleoptile and seedling shoot length. Therefore, Rht14 can be a used as an alternative to Rht-B1b for development of cultivars suitable for deeper sowing in dry environments and in conditions of conservation agriculture where crop residues are retained.

Characterization of Biostimulant Mode of Action Using Novel Multi-Trait High-Throughput Screening of Arabidopsis Germination and Rosette Growth.

Environmental stresses have a significant effect on agricultural crop productivity worldwide. Exposure of seeds to abiotic stresses, such as salinity among others, results in lower seed viability, reduced germination, and poor seedling establishment. Alternative agronomic practices, e.g., the use of plant biostimulants, have attracted considerable interest from the scientific community and commercial enterprises. Biostimulants, i.e., products of biological origin (including bacteria, fungi, seaweeds, higher plants, or animals) have significant potential for (i) improving physiological processes in plants and (ii) stimulating germination, growth and stress tolerance. However, biostimulants are diverse, and can range from single compounds to complex matrices with different groups of bioactive components that have only been partly characterized. Due to the complex mixtures of biologically active compounds present in biostimulants, efficient methods for characterizing their potential mode of action are needed. In this study, we report the development of a novel complex approach to biological activity testing, based on multi-trait high-throughput screening (MTHTS) of Arabidopsis characteristics. These include the in vitro germination rate, early seedling establishment capacity, growth capacity under stress and stress response. The method is suitable for identifying new biostimulants and characterizing their mode of action. Representatives of compatible solutes such as amino acids and polyamines known to be present in many of the biostimulant irrespective of their origin, i.e., well-established biostimulants that enhance stress tolerance and crop productivity, were used for the assay optimization and validation. The selected compounds were applied through seed priming over a broad concentration range and the effect was investigated simultaneously under control, moderate stress and severe salt stress conditions. The new MTHTS approach represents a powerful tool in the field of biostimulant research and development and offers direct classification of the biostimulants mode of action into three categories: (1) plant growth promotors/inhibitors, (2) stress alleviators, and (3) combined action.

Seed Priming with Gibberellic Acid (GA3) Alleviates Salinity Induced Inhibition of Germination and Seedling Growth of Zea mays L., Pisum sativum Var. abyssinicum A. Braun and Lathyrus sativus L.

Low seed germination, poor seedling establishment, and less crop productivity are commonly observed problems in salt-affected soils. Genetic modification of plants for creating good varieties and selection of crop plants that have best performance on saline soils are the major accomplishments done to minimize the problem. In addition, application of Gibberellic Acid (GA3) has been reported to increase germination percentage and seedling growth performance of crop plants under salt stress. The objective of the present study was therefore to investigate the effect of GA3 on germination and early seedling growth of three important crops under saline conditions. To this effect an experiment was conducted as factorial with completely randomized design with three replicates. The factors of the experiment were salinity with four levels (0, 4, 6, 8, and 12 dS/m), hormone (GA3 at 0.2 g/L versus no GA3) and the three crops (Zea mays L., Pisums sativum Var. abyssinicum A. Braun, and Lathyrus sativus L). Consequently, priming seeds of these crops with 0.2 g/L GA3 significantly improved germination percentage, reduced mean germination time, increased shoot and root length, and total weight of the crops (P < 0.05) when the salinity level is less than 8 dS/m. However, shoots of all crops performed better than the roots.

Identification of QTLs for tolerance to hypoxia during germination in rice

Direct seeding of rice as a method of crop establishment is increasingly being adopted by farmers as a means of saving labor and reducing costs. However, the method often results in a poor environment for germination as excessive water levels after seeding can cause poor seedling establishment and a concomitant reduction in yield potential, especially in submergence-prone areas. In this study, we discovered QTLs associated with tolerance of anaerobic germination (AG) in new genetic accessions using genotypic data derived from the Illumina 6K SNP chip. The mapping population developed for QTL analysis comprised 285 F2:3 plants derived from a cross between Tai Nguyen and Anda. In order to evaluate AG tolerance within the mapping population, phenotyping was carried out under anaerobic conditions for 21 days. Three QTLs associated with AG tolerance were identified in the population, qAG1a and qAG1b on chromosome 1 and qAG8 on chromosome 8 using composite interval mapping (CIM). The percentage of variance explained by these QTLs ranged from 5.49 to 14.14%. The lines with three QTLs (qAG1b + qAG1a + qAG8) demonstrated an approximate 50% survival rate under anaerobic conditions, while lines with two QTLs including qAG1b demonstrated survival rates of 36 and 32% after the treatment, respectively. The QTLs detected in this study may be used to improve AG tolerance during germination and may be combined with other QTLs for anaerobic germination to enhance adaptation to direct seeding and to broaden the understanding of the genetic control of tolerance of germination under anaerobic conditions.

Factors influencing the natural regeneration of the pioneering shrub Calligonum mongolicum in sand dune stabilization plantations in arid deserts of northwest China.

Calligonum mongolicum is a successful pioneer shrub to combat desertification, which is widely used for vegetation restoration in the desert regions of northwest China. In order to reveal the limitations to natural regeneration of C. mongolicum by asexual and sexual reproduction, following the process of sand dune stabilization, we assessed clonal shoots, seedling emergence, soil seed bank density, and soil physical characteristics in mobile and stabilized sand dunes. Controlled field and pot experiments were also conducted to assess germination and seedling emergence in different dune soil types and seed burial depths. The population density of mature C. mongolicum was significantly different after sand dune stabilization. Juvenile density of C. mongolicm was much lower in stabilized sand dunes than mobile sand dune. There was no significant difference in soil seed bank density at three soil depths between mobile and stabilized sand dunes, while the emergence of seedlings in stabilized dunes was much lower than emergence in mobile dunes. There was no clonal propagation found in stabilized dunes, and very few C. mongolicum seedlings were established on stabilized sand dunes. Soil clay and silt content, air‐filled porosity, and soil surface compaction were significantly changed from mobile sand dune to stabilized dunes. Seedling emergence of C. mongolicm was highly dependent on soil physical condition. These results indicated that changes in soil physical condition limited clonal propagation and seedling emergence of C. mongolicum in stabilized sand dunes. Seed bank density was not a limiting factor; however, poor seedling establishment limited C. mongolicum's further natural regeneration in stabilized sand dunes. Therefore, clonal propagation may be the most important mode for population expansion in mobile sand dunes. As a pioneer species C. mongolicum is well adapted to propagate in mobile sand dune conditions, it appears unlikely to survive naturally in stabilized sand dune plantations.

Agro-economic evaluation of potassium application in spring maize under early and late sown conditions

Although the yield potential of spring maize is much higher than autumn maize but high temperature at anthesis stage is one of the main problems in spring maize especially in late sown conditions which caused a synchronous pollination, fertilization and grain formation. Early sowing of the crop seems an ideal solution to escape the heat period but low temperature causes poor seedling establishment. Both temperature extremes osmotic and oxidative stresses are major reasons of economical crop damage. Potassium application may lessen these oxidative damages and crop stand establishment of maize under semi arid conditions of Faisalabad. Observations on number of plants per unit area, cobs per plant, grains per cob, 100-grain weight, grain yield, grain protein and oil contents were recorded by using standard procedures. The net income and benefit cost ratio were calculated to evaluate the most economical and profitable potassium level. Sowing dates affected significantly number of plants, cobs per plant, grains and 100-weight, grain yield, grain protein and oil contents while potassium application considerably improved grain yield through increasing crop stand under both early and late sown conditions by ameliorating stresses. It is concluded that the benefit cost ratio of 100 kg ha-1 potassium application is only beneficial under early planting on 1st February.Bangladesh J. Sci. Ind. Res. 52(4), 295-302, 2017

Melatonin application confers enhanced salt tolerance by regulating Na+ and Cl− accumulation in rice

The mitigating effects of melatonin (MT) treatment on salt-stressed seed germination capacity and of MT pretreatment (including the whole period of seed germination and seedling cultivation) on the salt tolerance of two rice (Oryza sativa L. ssp. japonica) cultivars, Liaojing 4 (LJ4, salt tolerant) and Nipponbare (Nipp, salt sensitive), and the related physiological and molecular events were investigated in this study. The results showed that when additional MT solutions (10–500 μM) were added, the NaCl-decreased seed germination potential (GP), germination index (GI) and vigor index (VI) of LJ4 and Nipp were clearly restored. When MT pretreatment occurred during the period of seed germination and seedling cultivation prior to NaCl stress, relative electrolytic leakage in roots and leaves clearly decreased and thus restored the root vigor and growth of both plants. This could be fulfilled by multiple physiological mechanisms. For example, improving seed germination ability (GP, GI and VI), strengthening root vigor, reducing Na+ and Cl− contents in roots and leaves (especially for Cl− in roots and Na+ in leaves), and enhancing the activities of antioxidant enzymes (such as catalase and superoxide dismutase) in roots and leaves resulted in a decrease in H2O2 level. Moreover, the reduced contents of Na+ and Cl− in the roots and leaves of both salt-stressed rice plants under MT pretreatment displayed clear relations with the enhanced transcription of OsSOS1 in roots and of OsCLC1 and OsCLC2 in roots and leaves. These results could indicate that soaking with MT during seed germination and/or root application of MT at the seedling stage are very simple operations that require small doses and can effectively solve the problems of low germination rate and poor seedling establishment in saline soils. Therefore, these results provide a theoretical basis and technical support for the chemical regulation of salt tolerance and cultivation practices of rice and other crops in saline areas.

Limitation of Improvement in Germination by Osmopriming of Differentially Aged Non-Orthodox Neem (Azadirachta indica) Seeds

This work involves physiological and biochemical features of seed ageing gauged from seed viability and vigour over the period of storage. Both conventional storage (natural ageing) and controlled deterioration (accelerated ageing) are resulted in loss of germination capacity and vigour as well as poor seedling establishment. Present findings indicate that both natural and accelerated ageing sustain similar pattern, except their mortality curve. In natural ageing, prior to entering sigmoidal type decline a period of relative stability exists; whereas in accelerated aging, such relative stability is absent. It is also observed that rate- controlling process of ageing (natural ageing slow whereas accelerated ageing fast) was dependent upon moisture content and temperature. These physical factors have negative linear correlation with seed viability. Membrane integrity and lipid peroxidation are associated with seed ageing, however peroxidation does not hold exact with accelerated ageing. Additionally, these aged seeds were exposed to osmopriming (controlled hydration) resulted in improved germination characterized by faster and uniform germination. For the first time, it was strongly established that osmopriming significantly improves the seed germination (about 12- 17%) until a critical level (up to 50% germination) during the ageing and thereafter priming does not support the process of improvement of germination. Such improvement prediction is important for physiologists and seed technologists to recruitment the degree of priming.

Globisporangium oryzicola sp. nov., causing poor seedling establishment of directly seeded rice.

A new species, Globisporangium oryzicola, was isolated from directly seeded rice seedlings, and from soils of paddy fields and an uncultivated field. Despite their different origins, five of the seven isolates studied caused poor seedling establishment of rice in a laboratory inoculation experiment. The species is characterized by oogonia with smooth-walled or sometimes one projection, with one to two antheridia, and aplerotic oospores. Hyphal swellings were rarely observed. Phylogenetic analyses based on the internal transcribed spacer region of the ribosomal RNA gene and mitochondrial cytochrome c oxidase subunit 1 and 2 genes confirmed that the species differed from other Globisporangium species. This novel species is described and illustrated in detail.

Effect of Trichoderma and fungicide on seedling establishment and yield performance of dry direct seeded boro rice

Poor seedling establishment and seedling mortality is the major barrier to optimum stand establishment in dry direct seeded boro rice. Experiments were carried out at the Agronomy Field Laboratory, Bangladesh Agricultural University (BAU), Mymensingh, Bangladesh during January to June 2013 to study the effect of Trichoderma and fungicide application on seedling establishment and yield performance of dry direct seeded Boro rice. The experiment comprised ten treatment combinations of Trichoderma and fungicides viz. seed treatment with Trichoderma (M1), seed treatment with Trichoderma+spraying of Thiovit (M2), seed treatment with Trichoderma + spraying of Propiconazole (M3), seed treatment with Trichoderma + spraying of Thiovit and Propiconazole (M4), spraying of Thiovit (M5), spraying of Propiconazole (M6), seed treatment with Thiovit + spraying of Propiconazole (M7), seed treatment with Propiconazole + spraying of Thiovit (M8), spraying of mixture of Thiovit and Propiconazole (M9), and control (no fungicide or Trichoderma ) (M10).The experiments used Randomized Complete Block Design (RCBD) with three replications. Experiment revealed that seed treatment with Trichoderma harzianum followed by spraying of Thiovit gave the highest yield of rice. The study concludes that Trichoderma and then application of sulphur fungicide at 20 days after sowing could be practiced for ensuring high seedling establishment and yield of rice under dry direct seeded system in boro season.J. Bangladesh Agril. Univ. 14(1): 37-42, June 2016

Agronomic manipulations can enhance the productivity of anaerobic tolerant rice sown in flooded soils in rainfed areas

Poor seedling emergence and establishment are a major restraint for adopting direct seeding in rice. This is especially critical in rainfed lowlands where floods can occur immediately after sowing, creating anaerobic conditions during germination and early seedling growth. Developing rice cultivars that can germinate in flooded soils will ensure good crop establishment. Several major quantitative trait loci (QTLs) for tolerance of anaerobic conditions during germination (anaerobic germination; AG) were identified from different landraces; and near isogenic lines (NILs) containing one of these QTLs (qAG-9-2, AG1) in the background of IR64 were developed. This study is an attempt to determine the effectiveness of AG1 QTL in improving germination of two IR64-AG NILs; IR 93312-30-101-20-3-66-6 (IR64–AG131) and IR93312-30-101-20-13-64-21 (IR64-AG132) sown under flooded conditions. The study also evaluated selected agronomic practices anticipated to further enhance crop establishment in flooded soils. IR64-AG NILs showed 81% and 217% higher plant populations over IR64-Sub1 and IR64, respectively, and this was also reflected as significantly higher grain yields. IR64-AG NILs mobilized relatively more starch into soluble sugars while submerged and maintained higher soluble sugar supply to the developing embryo resulting in faster and higher germination rates than the non-AG genotypes. Agronomic manipulations like higher seed rate (60kgha−1), better seeding methods and nutrient application improved seedling growth after germination and emergence, increasing plant height, leaf area, number of tillers and biomass accumulation. These improvements were reflected as higher grain yield even in the intolerant cultivar IR64. Application of 20% more phosphorus with the recommended N-P-K resulted in 21%, 16% and 19% higher grain yield in IR64-AG, IR64-Sub1 and IR64, respectively, over the control. The results established that combining proper crop establishment practices with tolerant genotype could enhance crop establishment in flooded soils using direct seeding methods, with consequent reduction in production costs and water use and subsequent increase in farmers’ income.

Implications of bacterial contaminated seed lots and endophytic colonization by Pseudomonas fuscovaginae on rice establishment

The economic impact of seedborne bacterial diseases on rice production provides a major motivation for research on seed health. This paper reports on the endophytic growth of a rifampicin‐marked strain of the seedborne rice pathogen Pseudomonas fuscovaginae. The bacterium was found in most tested seeds indicating that, even without visible discolouration, seed transmission is possible. Crushed discoloured seeds contained more bacterial cells than did non‐crushed discoloured seeds. These bacteria were released during seed soaking, contaminating clean seed and lowering seed germination. Cells of a rifampicin‐resistant strain of P. fuscovaginae, which had been inoculated onto rice seeds, were subsequently recovered from different growth stages and from different rice tissues, thereby indicating endophytic colonization. These results have implications for seedling establishment, as symptomless seeds do not assure disease‐free seeds, and the presence of seedborne bacteria results in poor germination and poor seedling establishment. Elimination of seedborne bacteria by soaking in sodium hypochlorite can increase seed germination. This could be used in developing control strategies, and, if practised regularly, reduce entry of seedborne disease‐causing organisms into crops, resulting in lower disease pressure.

Evaluation Seed-born Fungi of Rice [Oryza sativa L.] and that Effect on Seed Quality

Poor seedling establishment in rice is one of the problems in Guilan province as the second most important rice-growing locations in Iran. The aim of this study was to evaluate the contamination occurrence of rice seed in five locations of Guilan province to seed-borne fungi and their effects on germination characteristics. Five seed sample of Hashemi variety obtained from leading farmers from each location, and their germination characteristics and the rate of contamination to Fusarium moniliforme, Bipolaris oryzae, Aspergillus niger, A. flavus, Penicillium sp., Alternaria padwickii was evaluated using the PDA and standard blotter methods. The assessment results showed that among the seed-borne fungi, two species A. niger and A. flavus exhibited the highest severity in both methods. Samples from Rasht and Zeybaknar locations showed the most contamination to A. flavus and A. niger. A positive and significant linear relationship was observed between daily precipitation and relative humidity with severity of A. flavus and A. niger fungus. A. niger, A. padwickii, daily precipitation and average minimum temperature had the most influence on germination characteristics. Among the studied factors, A. niger had high negative impact compared to other factors on all rice seed germination characteristics. Among the study locations, quality of seeds in Rostam- Abad in terms of germination percentage, germination rate, germination uniformity and electrical conductivity had the best state. The results of this study showed that the low precipitation and low daily average humidity along with higher number of sunshine hours in the Rostam-Abad caused reduction in activity and abundance of fungi, led to improve the quality of produced seed.

【Short Report】Improvement of Rice Seedling Establishment on Sulfate-Applied Submerged Soil by Seed Coating with Poorly SolubleMolybdenum Compounds

Although direct seeding is expected to be a labor-saving method in rice cultivation, poor seedling establishment is a major obstacle to widespread use of this practice. I previously reported that the seedling establishment of rice sown on sulfate-applied submerged soil was improved by the application of potassium molybdate to the soil. In this study, I investigated the effects of seed coating with poorly soluble molybdenum compounds on the seedling establishment to reduce the necessary amount of molybdenum (Mo). Seed coating with poorly soluble Mo compounds improved the seedling establishment in sulfate-applied submerged soil. Especially, ammonium phosphomolybdate and potassium phosphomolybdate were more effective and difficult to impair the seedling establishment even by seed coating of excessive amounts. Mo trioxide, which is a cheapest Mo compound, was also effective. Accordingly, seed coating with these Mo compounds would have the potential to improve rice seedling establishment in sulfur-rich submerged soil.