Use of Ethylene-Producing Bacteria for Stimulation of Striga spp. Seed Germination

Striga spp. are obligate root-parasitic flowering plants that threaten cereal and legume production, and consequently human well-being, in Africa. Successful control depends on eliminating the seed reserves of Striga spp. in soil and preventing parasitism. A proven method of eliminating these seed reserves is soil-injection of ethylene gas. This method was used successfully in the United States to control Striga asiatica, but injection of ethylene gas is potentially dangerous, very costly, and generally unsuitable in Africa. The bacterium Pseudomonas syringae pathovar glycinea synthesizes relatively large amounts of ethylene. In this study a laboratory procedure was developed for testing strains of P. syringae pv. glycinea for efficacy in stimulating germination of seeds of Striga spp. The procedure allows comparisons among bacteria, volatile compounds, root exudates, and synthetic stimulants for germination of Striga spp. seeds. Seeds of three Striga spp. were tested over a 10-month period. No seed germination was ever observed with sterile water. When compared across Striga spp. the bacterial strains were consistently better stimulators of germination of seeds of the parasites than ethylene gas or root pieces of a Vigna unguiculata cultivar known to stimulate germination of parasite seeds. The strains were as effective in germinating S. aspera and S. gesnerioides seeds as a synthetic germination stimulant. Our results showing that ethylene-producing bacteria are highly effective in promoting seed germination in Striga spp. suggest that these bacteria may provide a practical means of biological control of Striga spp. in Africa and other locations.     

Quick and accurate detection of Sclerotinia sclerotiorum and Phomopsis spp. in soybean seeds using qPCR and seed‐soaking method

Seed‐borne pathogenic fungi can cause serious damage to soybean crops by reducing the germination, vigour and emergence of the seeds. Special attention should be paid to pathogen detection in seeds to prevent its introduction in disease‐free areas. Considering the importance of rapid and successful diagnosis of seed‐borne pathogenic fungi in soybeans, this study evaluated a method to detect Sclerotinia sclerotiorum and Phomopsis spp. in seeds using quantitative polymerase chain reaction (qPCR). Naturally infested samples were subjected to detection using qPCR and blotter test, and the findings were compared. Using soybean seeds soaked in water, both pathogens were detected at an infestation level up a 0.0625% (one infected seed out of 1,599 healthy seeds) by qPCR. This technique allowed the detection of 300 fg of S. sclerotiorum and 30 fg of Phomopsis spp. DNA in the seed samples. Phomopsis spp. was detected in 40.7% of the evaluated seed batches (81 batches) and S. sclerotiorum was detected in 32.1% of the evaluated batches, although most of the seeds had low infestation levels. It was up to 28.5 times more efficient to use qPCR rather than blotter test to detect pathogens with a low incidence of occurrence in soybean seeds. If routinely used to test healthy seeds, qPCR would contribute to reducing soybean losses due to diseases as well as decreasing the costs required to control those diseases.     

Winged bean (Psophocarpus tetragonolobus (L.) DC) as a substrate for growth and aflatoxin production by aflatoxigenic strains of Aspergillus spp.

The mold flora of seeds of twelve varieties of winged beans were determined both before and after surface disinfections. When seeds were surface disinfected, molds were detected in 73% of the seeds whereas 81% of the seed that was not disinfected produced molds. Aspergillus spp. were most frequently present while Penicillium spp. occurred in seed of 4 varieties and in less than 4% of the seed. Twelve isolates of A. flavus and A. parasiticus were examined for their ability to produce aflatoxins. Whether aflatoxins were produced and the amount of each varied according to the origin of the isolate and the species of Aspergillus. For example all A. flavus isolates produced at least 2 aflatoxins whereas 4 of the A. parasiticus isolates were nontoxigenic. When ground seeds of winged beans were inoculated with an aflatoxigenic strain of A. parasiticus the level of aflatoxins that occurred varied with the variety. All of the varieties supported greater aflatoxin production than peanuts and 6 of the 12 winged bean varieties gave higher levels of aflatoxins than rice.     

SEM observations on seeds ofStriga spp. andBuchnera americana (Scrophulariaceae)

Seeds of the root parasitesStriga (several spp.) andBuchnera americana were examined by means of SEM. The surface patterns of the seeds in both genera resemble each other closely, especially those ofS. angustifolia andB. americana. SomeStriga spp. can be clearly distinguished by their surface characteristics, while this is quite difficult in others. The taxonomic value of the seed surface features ofStriga andBuchnera is discussed.     

Winged bean (Psophocarpus tetragonolobus (L.) DC) as a substrate for growth and aflatoxin production by aflatoxigenic strains of Aspergillus spp

The mold flora of seeds of twelve varieties of winged beans was determined both before and after surface disinfections. When seeds were surface disinfected, mold fungi were detected in 73% of the seeds whereas 81% of the seed that was not disinfected produced mold fungi. Aspergillus spp. was most frequently present while Penicillium spp. occurred in seed of 4 varieties and in less than 4% of the seed. Twelve isolates oiA. flavus and A. parasiticus were examined for their ability to produce aflatoxins. Whether aflatoxins were produced and the amount of each varied according to the origin of the isolate and the species of Aspergillus. For example all A. parasiticus isolates produced at least 2 aflatoxins whereas 4 of the A. parasiticus isolates were non-toxigenic. When ground seeds of winged beans were inoculated with an aflatoxigenic strain of A. parasiticus the level of aflatoxins that occurred varied with the variety, however, the level of aflatoxin was higher in winged bean than in peanut tissue and 6 of the 12 winged bean varieties contained higher levels of aflatoxins than rice.     

IAA production during germination of Orobanche spp. seeds

Broomrapes (Orobanche spp.) are parasitic plants, whose growth and development fully depend on the nutritional connection established between the parasite and the roots of the respective host plant. Phytohormones are known to play a role in establishing the specific Orobanche-host plant interaction. The first step in the interaction is seed germination triggered by a germination stimulant secreted by the host-plant roots. We quantified indole-3-acetic acid (IAA) and abscisic acid (ABA) during the seed germination of tobacco broomrape (Orobanche ramosa) and sunflower broomrape (O. cumana). IAA was mainly released from Orobanche seeds in host-parasite interactions as compared to non-host-parasite interactions. Moreover, germinating seeds of O. ramosa released IAA as early as 24 h after the seeds were exposed to the germination stimulant, even before development of the germ tube. ABA levels remained unchanged during the germination of the parasites' seeds. The results presented here show that IAA production is probably part of a mechanism triggering germination upon the induction by the host factor, thus resulting in seed germination.     

THE SURFACE DECONTAMINATION OF SEEDS TO PRODUCE AXENIC SEEDLINGS

A variety of sterilizing agents were tested to develop a standard procedure for surface decontaminating seeds to produce axenic seedlings. The use of calcium hypochlorite (0.5% phosphate buffer, pH 6) for 10 min followed by three sterile water rinses was among the most effective agents, and it did not injure some species as did sodium hypochlorite, formaldehyde, ethylene oxide and mercuric chloride. Some species contained internal microbes requiring severe treatments which killed or injured the seedling, while other species were “decontaminated” with a sterile water rinse. The percentage of seeds with internal microbes varied considerably among plant species, seed lot, and the length of seed storage. Thus, with seeds not easily decontaminated, screening of additional seed lots would be more profitable than testing additional decontamination agents. Release of microbes from the seed's interior is associated with germination, and microbial testing must last at least 11 days. Nutrient agar permitted growth, although the seedlings outgrew petri plates too quickly for adequate certification. These seedlings were transferred to nutrient agar in quart jars in which an internal pool of broth was periodically agitated to permit microbial sampling of the leaves while the plant grew.     

Dormancy in red rice. IV. Response of unimbibed and imbibing seeds to nitrogen dioxide

Nitrogen dioxide at 4 to 8 ml 1⁻¹ breaks dormancy of dehulled, unimbibed seeds of red rice ( Oryza sativa L.) with minimum exposure times to the gas of 20 min or less. The response is independent of incubation medium pH following treatment. Germination is complete within 2 days but proceeds 4 to 6 h more slowly than non-dormant controls. The magnitude of response at a constant NO₂ dose is dependent upon initial seed moisture. There was less than 40% germination at 9.6% initial moisture while germination was 95% at 12% initial moisture. NO₂ treatment also breaks dormancy of imbibing, dehulled seeds, but the response is dependent upon the pH of the medium. Dormancy is broken at pHs close to the pK_a of nitrous acid. Intact, unimbibed or imbibing seeds respond to NO₂ treatment only if partially dry-afterripened prior to exposure.     

植物挥发性物质对落叶松球果花蝇的驱避效果

为研究外源植物挥发性物质对落叶松球果花蝇（Strobilomyia spp.）对寄主定位的干扰作用,在哈尔滨市和大兴安岭加格达奇兴安落叶松（Larix gmelinii）种子园,用松节油、樟脑、丁香油进行了室内生测和林间喷施试验。在室内,球果花蝇对1％松节油的反应率为94.23％,与1％丁香油、3％松节油、20％丁香油相比差异显著;对1％樟脑的反应率为87.92％。球果花蝇对2％丁香油的反应率最低,仅为16.30％。在室内及林间,1％松节油及1％樟脑对球果花蝇都表现为驱避作用。1％松节油及其对照对球果花蝇的驱避效果最好,平均每果虫数较清水对照的3.51分别降低了2.85和2.66,使球果被害率降低了57.0％和46.2％,种子被害率分别降低了24.7％和27.7％。其次是1％脑及其对照,每果虫数较清水对照降低了1.83和1.44个,球果被害率分别降低了9.0％和30.7％,种子被害率分别下降了12.2％和26.9％。1％丁香油对花蝇在室内表现为诱引作用,在林间表现为驱避作用。在喷施3种挥发性物质及其对照后,各个处理的球果挥发性物质主要组分的总量都较清水对照增加,各处理的α-蒎烯相对含量较清水对照大幅度降低,降低幅度在13.56％-24.83％之间;各处理的β-罗勒烯都有不同程度的增加。β-蒎烯、3-蒈烯、月桂烯、水芹烯的相对含量在各处理中升降不一。     

Oils as adhesives for seed inoculation and their influence on the survival of Rhizobium spp. and Bradyrhizobium spp. on inoculated seeds

Mineral oil, peanut oil and soybean oil were compared with water and gum arabic for their suitability as adhesives for seed inoculation with peat inoculants. Inoculated seeds were stored at 4, 28 and 34°C, and sampled after 1, 3 and 9 days to determine the survival of rhizobia. Germination and nodulation tests were performed on the inoculated seeds. Results showed that oils were suitable adhesives for peat inoculants. Although the oils initially bound less inoculant to the seed, the number of surviving rhizobia was similar to that obtained by the gum arabic treatment after storage at 28 and 34°C for 3 and 9 days. An interesting finding of this experiment was that peanut and soybean oils were superior to gum arabic in supporting significantly higher numbers of chickpea rhizobia at 34°C. Inoculated seeds tested for germination and nodulation showed no adverse effects from the oil treatments. Oils hold good potential as adhesives for seed application in inoculation technology.H.J. Hoben and P. Somasegaran are with the NIFTAL Project, University of Hawaii, 1000 Holomua Avenue, Paia, HI 96779-9744, USA. Nwe Nwe Aung is with the Institute of Agriculture, Yezin, Pyinmana, Burma. Ui-Gum Kang is with the Yeongnam Crop Experiment Station, Rural Development Administration, P.O. Box 6, Milyang, Korea.     

Factors Influencing Seed Set in Triploid Musa spp. L. and Production of Euploid Hybrids

Seed set in triploid Musa spp. L. is very low due to high levelsof sterility. This makes cross breeding of plantain and bananadifficult. Nonetheless, several triploid plantain and bananacultivars produce seeds after hand pollination with diploidparents. This paper reports results about the pattern of seedvariation, success of in vitro germination and hybrid productionafter triploid-diploid crosses. Between-and within-clones differencesin seed set were observed. ABB cooking bananas had the highestrates of seed production followed by AAB French plantains. Plantainsproduced more diploid than tetraploid offsprings after triploid-diploidcrosses, which suggests that meiosis resulted in the productionof balanced haploid gametes (n = x) due to normal chromosomebehaviour between homologous genomes. Seed set variation withinclones was influenced by both the production of 2n (= 3x) gametesin the triploid parent and climatic factors. Indeed, seed production,embryo and seed germination success, and euploid and tetraploidhybrid production followed a pattern of seasonal variation reachinga peak in September. High frequency of seed with tetraploidembryos was obtained in the period from January to mid-March.The results demonstrate that production of desirable tetraploidswould be more efficient when hand pollinations are done underhigh temperature, high solar radiation and low relative humidity.These seem to be the most convenient conditions for relativelyhigh production of 2n eggs as compared to haploid gametes.Copyright1995, 1999 Academic Press Banana, fertility, embryo culture, Musa spp. AAA group, Musa spp. AAB group, Musa spp. ABB group, plantain, ploidy, seed set, 2n gametes     

Weedy adaptation in Setaria spp. V. Effects of gaseous environment on giant foxtail (Setaria faberii) (Poaceae) seed germination

The effects that naturally occurring gases (oxygen, nitrogen, carbon monoxide) may cause in dormant giant foxtail (Setaria faberii) seed germination under favorable temperature and moisture conditions were investigated. The germination responses to gas mixtures supported the hypothesis that S. faberii germination behavior is regulated by the amount of oxygen taken into hydrated seed over time. Setaria faberii seed germination was markedly affected by O(2) concentration (in N(2)) above and below that of air (20% O(2)): the largest increase in germination (from 37 to 60%) occurred between 20-25% O(2); between 0-10% O(2), germination increased from 0-30%; and surprisingly germination at 10 and 20% O(2) was similar. These observations reveal an asymmetrical response to incremental changes in O(2) above and below that typically found in agricultural soils. Carbon monoxide had opposite effects on S. faberii germination in air depending on concentration, stimulation, and inhibition: germination increased from 37 to 56% with the addition of 1% CO, but decreased from 37 to 14% with 75% added CO. An explanation may be that there are two separate effects of CO, each occurring in different physiological systems of dormant seeds at the same time. At high concentrations (75%) in air CO inhibited seed germination, probably by inhibiting mitochondrial respiration. But low CO concentrations (0.1 or 1%) in air stimulated seed germination. It was not apparent which physiological system(s) CO and O(2) affected. It seems unlikely that CO-stimulated germination arises from effects on the respiratory apparatus, but may be a consequence of CO interactions with an as yet unknown physiological factor in the seed. We provide a model of Setaria spp. dormancy consistent with its seed morphology, the gas-germination data, and the hypothesized second physiological factor that may be involved in CO stimulated germination.     

Isolation of Salmonella spp. from liquid and solid excreta prior to and following ensilage in ten swine farms located in central Mexico

A study was carried out to define selected bacteriological characteristics of residues from 10 swine farms, 5 with or without prior clinical enteric disease (PCED) and to determine the effect of ensilage on the bacteria present in the solid fraction. At each farm, samples were taken from the sedimentation basin (SB), the solid fraction (SF), and the liquid fraction (LF). For each sample, CFU/g for enteric bacteria were quantified; Salmonella spp. were isolated and typified. Solid phase samples from each farm were used to prepare the ensilage, with a mixture of solids (80%), sorghum (12%) and molasses (8%). The quantity of enteric bacteria was significantly greater in farms without PCED (P < 0.05). Salmonella enterica were isolated from 8/10 of the farms with and without PCED; in 8 from SB; in 6 from LF; and in 5 from SF. Enteric bacteria were not isolated from silage, therefore, ensilage may be an alternative treatment for excreta that allows the elimination of pathogens such as Salmonella spp.     

Effects of Controlled Deterioration and Osmoconditioning on Germination and Nuclear Replication in Seeds of Pepper (Capsicum annuumL.)

Unaged and controlled deteriorated (45°C for 4, 6 or 10 d) samples of a pepper seed lot were subjected to osmoconditioning in PEG at osmotic potentials of -1.1 and -1.5MPa for 6, 10 or 14d. The effect of osmoconditioning on nuclear replication activity was examined using flow cytometry.Priming of unaged seeds always induced nuclei of embryo root tips to enter the synthetic phase. In accordance with our previous findings the amount of induced nuclear replication activity was higher after priming at the lowest osmotic potential. Under the same osmotic potential the amount of priming-induced replication was correlated with the length of priming treatment and its efficiency in improving seed performance. However, the 14d treatment at -1.5MPa was as effective on seed performance as the 6d treatment at -1.1MPa, which induced higher numbers of nuclei to enter the synthetic phase.Osmoconditioning on controlled deteriorated seeds had different effects on seed germination depending on the degree of seed deterioration. Under the same osmotic treatment, the amount of priming-induced DNA synthesis was lower than in unaged seeds or was not induced at all. The activation of nuclear replication by osmoconditioning, therefore, appears influenced by the level of seed deterioration. In less deteriorated seeds (45°C for 4d), 14d priming at -1.1MPa caused shortening of mean germination time compared with unaged seeds, but was less effective in inducing nuclear replication.The effect of the length and osmotic potential of priming on nuclear replication and the role of molecular processes, other than DNA synthesis, in improving seed performance are discussed.     

Hot Acidified Cupric Acetate Soaks for Eradication of Xanthomonas campestris from Crucifer Seeds

Acidified cupric acetate soaks were tested for eradication of Xanthomonas campestris from naturally infected crucifer seeds. The pathogen was eradicated from seeds by soaking in 0.5% cupric acetate dissolved in 0.005 N acetic acid for 20 min at 35, 40, 45, and 50°C but not 25°C. Moreover, normal bacterial flora of crucifer seeds and the seed-borne Phoma lingam and Alternaria spp. were reduced by 95, 92, and 81%, respectively, after the cupric acetate treatment at 40°C. The seed germination percentage was generally reduced, but the amount of reduction depended upon the treatment temperature and plant cultivar. At 50°C, less than 50% of the seed of all 12 cultivars tested germinated, whereas at 40°C more than 50% of the seeds of most cultivars germinated. Treating seeds in cupric acetate at 40°C should prove useful for eradicating X. campestris from seeds of breeding lines and stock seed used for hybrid seed production. Furthermore, a significant reduction in total bacterial flora and seed-borne fungi suggests the usefulness of the treatment for other microorganisms associated with other seeds or foodstuffs.     

Effect of Storage on the Survival and Biocontrol Activity of Pythium oligandrum in Pelleted Sugar Beet Seed

Seeds of sugar beet were pelleted with oospores of Pythium oligandrum and stored for 6 years at 8 20IC. Mycelium of P. oligandrum grew from pelleted seed when plated on cornmeal agar (CMA) within 48 h from 100% of seeds stored for 0, 2 and 4 years, and from 93% of seeds stored for 6 years. The germination of oospores removed from pelleted seed immediately after pelleting was 30% on CMA after 18 h of incubation, but storage gradually reduced germination to only 16% after 48 h of incubation for oospores removed from seed stored for 6 years. The biocontrol activity of P. oligandrum -pelleted seed was also tested after 6 years of storage in mixes of soil naturally infested with Pythium spp. and Aphanomyces cochlioides , and sand. P. oligandrum -pelleted seed had no effect in reducing damping-off due to the combined effect of Pythium spp. and A. cochlioides in 5 and 1% (v/v) soil-sand mixtures. However, in the 1% (v/v) soil-sand mixture, P. oligandrum significantly reduced Pythium spp.-induced damping-off from 33 to 26%.     

Seed treatment with lactic acid bacteria against seed-borne pathogens of spring wheat

Antifungal potential of lactic acid bacteria (LAB) such as Lactobacillus sakei KTU05-6, Pediococcus acidilactici KTU05-7 and Pediococcus pentosaceus KTU05-8, KTU05-9 and KTU05-10 was tested on naturally contaminated wheat seeds. LAB influence on fungal growth on kernels, seedling diseases and seed germination was examined by laboratory and field experiments. KTU05-10 was selected and later used for seed treatment as solitary strain and in two- or three-component mixtures with KTU05-7 and KTU05-6. The occurrence of Fusarium spp. on wheat kernels in agar plate assays was decreased by seed treatment with all LAB cultures, and the efficacy of each strain depended on incubation temperature. Inoculation of wheat kernels with strains of solitary KTU05-10 and in mixtures with KTU05-7 and KTU05-6 significantly reduced the incidence of Fusarium spp., Bipolaris sorokiniana and Alternaria spp. LAB influence on seed germination and seedling diseases was observed in laboratory and field experiments, but in most cases, this influence was insignificant.     

Longitudinal evaluation of the efficacy of heat treatment procedures against Legionella spp. in hospital water systems by using a flow cytometric assay

Legionella spp. are frequently isolated in hospital water systems. Heat shock (30 min at 70°C) is recommended by the World Health Organization to control its multiplication. The aim of the study was to evaluate retrospectively the efficacy of heat treatments by using a flow cytometry assay (FCA) able to identify viable but nonculturable (VBNC) cells. The study included Legionella strains (L. pneumophila [3 clusters] and L. anisa [1 cluster]) isolated from four hot water circuits of different hospital buildings in Saint-Etienne, France, during a 20-year prospective surveillance. The strains recovered from the different circuits were not epidemiologically related, but the strains isolated within a same circuit over time exhibited an identical genotypic profile. After an in vitro treatment of 30 min at 70°C, the mean percentage of viable cells and VBNC cells varied from 4.6% to 71.7%. The in vitro differences in heat sensitivity were in agreement with the observed efficacy of preventive and corrective heating measures used to control water contamination. These results suggest that Legionella strains can become heat resistant after heating treatments for a long time and that flow cytometry could be helpful to check the efficacy of heat treatments on Legionella spp. and to optimize the decontamination processes applied to water systems for the control of Legionella proliferation.     

Einfluß der Behandlung von Rübensaatgut mit Rhizosphärebakterien auf den Befall durch Pilze der Gattung Pythium I. Antagonistische Wirkung verschiedener Bakterienisolate gegenüber Pythium spp.

Abstract The influence of a seed-dressing with rhizosphere bacteria on the infection of sugarbeet by fungi of the genus Pythium I. Antagonistic effect of different bacterial isolates towards Pythium spp.
Seed treatment with selectively isolated rhizosphere bacteria from the fluorescent pseudomonad group can protect sugar beet seedlings from damping-off caused by species of Pythium. The antagonistic rhizobacteria were equally effective in different soil substrates, both unsterilized and steam-sterilized. Antagonistic activity of an isolate was similar within seeds of a sugarbeet cultivar but different when different cultivars were compared. The number of bacteria adhering to the seed of eachcultivar which influenced the level of antagonism to Pythium infection, varied with seed morphology. A mixture of the three different isolates did not increase antagonistic activity when compared to the activity of the isolates individually.     

Plasma-treated silk fibroin nanofibers for skin regeneration

Silk fibroin (SF) nanofibers were prepared by electrospinning and treated with plasma in the presence of oxygen or methane gas to modify their surface characteristics. The surface characteristics of the SF nanofibers after plasma treatment were examined using contact angle measurements and XPS analysis. The hydrophilicity of the electrospun SF nanofibers decreased slightly by the CH₄ plasma treatment. On the other hand, the hydrophilicity of the SF nanofibers increased greatly by an O₂ plasma treatment. The O₂-treated SF nanofibers showed higher cellular activities for both normal human epidermal keratinocytes (NHEK) and fibroblasts (NHEF) than the untreated ones.