Feeding and dispersion of Spodoptera exigua larvae and its relevance for control with a nuclear polyhedrosis virus

On chrysanthemum crops the larvae of the beet armyworm Spodoptera exigua (Hübner) (Lep.: Noctuidae) moved upwards to the top of plants after hatching and predominantly fed on the upper foliage layers. On tomato, however, the larvae did not move upwards and mainly fed on the lower leaves. On chrysanthemums up to the fourth instar most feeding occurred at the underside of foliage while the upper-epidermis remained intact. Larvae dispersing from a single egg batch of 35 eggs damaged about 90 small and 50 tall chrysanthemum plants during their development. The successive larval stages contributed respectively 0.1, 0.4, 4, 20 and 75 percent to the total foliage consumption.The results indicated that the virus preferably should be applied to the lower leaves of tomatoes and chrysanthemums when young instars are present, but to the upper-middle and top leaves of chrysanthemums when the larvae are older than second instars.

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Résumé La consommation et la dispersion des chenilles de Spodoptera exigua sont examinées sur chrysanthèmes et tomates de serre. Les adults déposent les oeufs généralement au feuilles près du sol. Apres l'éclosion les chenilles graduellement se mouvent en haute dans les chrysanthèmes et consomment principalement les feuilles les plus hautes. Dans tomate, cependant, les chenilles s'alimentent principalement au feuilles près du sol.Pendant leur dévelopment les chenilles originaires d'une seule pond de 35 oeufs peuvent endommager environ go petits ou so hautes crysanthè mes. Jusqu'à la quatrième stade larvale les chenilles s'alimentent principalement avec le surface inférieure des feuilles, sans consommer l'épiderme supérieure.Les cinq stades larvales contribuent respectivement 0,1, 0,4, 4, 20 et 75% a la consommation totale des feuilles de chrysanthème.Les resultats des expériments sur la conduite larvale suggestent que les viruses de la polyédrose nucléaire doivent être appliqués préférablement sur la face inférieure des feuilles bas de chrysanthème et de tomate avant que les chenilles se développent a la troisième stade larvale. Quand les larves sur chrysanthèmes sont déja dans le troisième stade larvale, application du virus sur les feuilles plus haute probablement donnait des resultats optimal.

     

Nuclear polyhedrosis virus for control of Spodoptera exigua larvae on glasshouse crops

the efficacy of a nuclear polyhedrosis virus, SeNPV, for controlling larval populations of the beet armyworm, Spodoptera exigua (Noctuidae) was studied in chrysanthemum, gerbera, kalanchoë and tomato crops in glasshouses. Applications of 1×10⁸ PIBs/m² on the various crops resulted in 95–100% larval mortality. Virus applications caused comparable levels of mortality in populations of early and late instar larvae. Reduction in feeding damage to the crops, however, was more pronounced when the larvae were early instars at the time of virus application. Single applications with the virus resulted in higher levels of larval mortality as double applications with 0.1% methomyl and diflubenzuron.The virus appears to be a potential control agent for the beet armyworm in Dutch glasshouses.

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Résumé Les résultats d'applications d'un virus de la polyédrose nucléaire contre des populations de chenilles de Spodoptera exigua sont examinés dans des chrysanthèmes, gerberas, kalanchoës et tomates. Une dose de 1×10⁸ PIBs/m² résulte à 95–100% mortalité larvale dans tous les végétaux. L'effet sur chemilles de première et seconde stade larvale et sur chenilles de troisième et quatrième stade larvale était pareille. Malgré le niveau élevé du mortalité larvale les végéteaux étaient damagés sérieusement, particulièrement quand le virus était appliqué contre des chenilles de troisième et quatrième stade larvale.Comparée avec des pesticides chimiques, méthomyl et diflubenzuron, applications de virus résultent à un mortalité larvale plus haute. Le conclusion était que le virus est un candidat sérieus pour l'utilisation dans le lutte biologique contre les chenilles de S. exigua dans des serres en Pays Bas.

     

Dormancy break of celery (Apium graveolens L.) seeds by plant derived smoke extract

Seed dormancy of a highly-dormant cultivar of celery (Apium graveolens L.) was broken by combinations of plant-derived smoke extract or N⁶-benzyladenine (BA) and gibberellins A_4/7 (GA_4/7) in the dark at temperatures between 18 and 26°C. A less dormant cultivar which responded to GA_4/7 alone showed no additional response to smoke extract or BA. Neither smoke extract nor BA affected either cultivar in the dark in the absence of GA_4/7. The partial dormancy-breaking effect of short exposures to red-light was also enhanced by smoke extracts in this highly-dormant cultivar. The results suggest that smoke extracts act in a similar way to cytokinins, by enhancing gibberellin activity in the celery seed system.Abbreviations BA N⁶-benzyladenine - GA_4/7 A₄ and A₇ gibberellin mixture     

Effect of CryIC toxin from Bacillus thuringiensis on larval feeding behavior of Spodoptera exigua

The lack of data on the effect of Bacillus thuringiensis (B.t.) toxins on larval feeding behavior of the pest Spodoptera exigua (Hübner) (Noctuidae: Amphypyrini) prompted us to investigate the effect of three delivery systems of CryIC, a commercial formulation, inclusion bodies, and the activated CryIC toxin. The commercial formulation was the least and CryIC toxin the most lethal form to neonates of susceptible colonies. All but two of the treatments in choice tests with neonates and third instars showed significant avoidance of B.t. treated diet, with greater proportion of larvae from susceptible (UCR-S and AUBURN-S) and resistant (AUBURN-R) colonies on untreated diet than on diet treated with any of the CryIC forms and concentrations tested. Furthermore, third instars consumed significantly more control than treated diet for all CryIC forms, colonies and concentrations. The avoidance of CryIC toxin by neonates and third instars strongly suggests that CryIC, which also is present in the commercial formulation and in the inclusion bodies, is responsible for eliciting avoidance behavior by S. exigua larvae. Behavioral observations of third instars in a no-choice test on either treated or control diet indicated that questing behavior in susceptible larvae appears to be positively related with presence of CryIC toxin in the diet. Furthermore, resistant third instars were on the whole more active than susceptible thirds on both treated and control diet. Resistant thirds raised on CryIC treated diet (AUBURN-RC) spent more time eating treated diet than resistant larvae raised on control diet (AUBURN-R), suggesting that diet conditioning plays an important role on feeding behavior of S. exigua. The implications of these results are discussed.     

Phenotypic characteristics and relative proportions of three genotypic variants isolated from a nucleopolyhedrovirus of Spodoptera exigua

US2A, US2D, and US2F are three in vivocloned genotypic variants from the wild-type strain of a Spodoptera exiguanucleopolyhedrovirus (SeMNPV) isolated in Florida (USA) and is the active component of the commercial bioinsecticide Spod-X^®. These variants were compared in terms of pathogenicity (LD₅₀), speed of kill (expressed as mean time to death) and viral progeny productivity (OBs/larva). LD₅₀values were similar for the three cloned genotypes. The mean time to death value for US2D (113.7 h) was significantly higher than those of US2A (31.7 h) and US2F (27.8 h). Virus yield was determined for L₄larvae infected with the estimated LD₉₉. US2D infected larvae attained higher weight than those infected with US2A and US2F, and produced a higher OB yield than larvae infected with US2A or US2F. An outstanding feature of US2F, in contrast to US2A and US2D, was its inability to disrupt the teguments of NPV-killed larvae. To study the relative proportion of the three genotypic variants throughout successive passages, S. exigualarvae were originally infected with a viral inoculum containing a 1:1:1 mixture of the three genotypes. After three successive passages, US2D was no longer detected in either of the three replicate experiments performed, while US2A was the predominant genotype in all of them, and US2F remained at similar proportions throughout the three passages. The influence of the phenotypic characteristics of the three variants on their relative proportions in mixed infections is discussed.     

Climbing by newly hatched larvae of the spotted stalk borer Chilo partellus to the top of sorghum plants

The biological impact of consumption and utilization of celery was examined for the generalist herbivore, Spodoptera exigua (Hübner). An analysis of leaves and petioles demonstrated that both plant parts contained high levels of water (>85%), but that leaves contained twice as much total organic nitrogen as petioles. Developmental and reproductive rates were significantly higher (P<0.01, t-test) for larvae fed on leaves. Penultimate and final instars consumed significantly more (P0.05, t-test) dry weight of plant material when fed petioles as opposed to leaves. Although growth rates were similar regardless of food source for penultimate instars, conversion of food to body weight was lower for larvae limited to petioles. In the final instar, both growth and conversion rates were lower for larvae fed petioles than for those given leaves. Thus, since larvae exhibit preferences for the nutritionally less suitable petioles during later larval stages, environmental factors other than nutrition must influence movement and distribution of S., exigua in celery.

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Résumé L'impact biologique de la consommation et de l'utilisation du céleri a été examiné sur un herbivore généraliste Spodoptera exigua Hübner. Une analyse de feuilles et de pétioles montre que ces deux parties de la plante ont une haute teneur en eau (>85%), mais que les feuilles contiennent deux fois plus d'azote organique total que les pétioles. Les taux de développement et de reproduction on été significativement plus élevés (<0,01 test t) pour les chenilles nourries sur feuilles. Les 2 derniers stades ont consommé significativement plus (P<0,05 test t) de poids sec de matière végétale en s'alimentant sur pétioles qu'en s'alimentant sur feuilles. Bien que les taux de croissance aient été voisins quel que soit l'aliment pour les avant-derniers stades, la conversion d'aliment en poids de corps était inférieure pour les chenilles ne consommant que des pétioles. Au dernier stade, tant les taux de croissance que de conversion des chenilles élevées sur pétioles étaient inférieurs à ceux des chenilles élevées sur feuilles. Ainsi, puisque les chenilles présentent une préférence pour les pétioles moins nutritifs au dernier stade larvaire, des paramètres écologiques autres que l'alimentation doivent influencer les mouvements et la distribution de S. exigua sur céleri.

     

An evaluation of some natural enemies of Spodoptera exigua on sugarbeet in northern California

Eggs and small to medium-sizedlarvae of Spodoptera exigua (Hübner)(Lepidoptera: Noctuidae) are exploited by acomplex of natural enemies in spring-plantedsugarbeet fields in northern California. Fieldstudies revealed that predation on sentinel eggmasses ranged from 20 to 100%egg mass;predation rate was lowest in fields previouslytreated with methomyl and highest innon-treated fields. Predators typicallydestroyed all of the eggs in a given egg mass;percentage predation per egg mass was densityindependent (spatial context). Survival of eggs(to neonate larvae) in cages that excludedpredators ranged from 80 to $>$90%. Theegg-predator guild consisted of adults andnymphs of Orius tristicolor(White)(Anthocoridae), Nabis americoferusCarayon (Nabidae), Lygus hesperus Knight(Miridae), and Geocoris punctipes (Say)(Geocoridae); larvae of Chrysoperlacarnea (Stephens) (Chrysopidae); and adults ofCollops vittatus (Say) (Melyridae). Laboratory evaluation revealed that largelarvae of C. carnea and the adults of theother species (except for O. tristicolor)could consume 100 eggs of S. exigua in a48 h period. The parasite guild associatedwith small and medium-sized larvae consisted ofthree species: Hyposoter exiguae(Viereck) and Pristomerus spinator (F.)(Ichneumonidae), both larval endoparasites; andChelonus insularis Cresson (Braconidae),an egg-larval endoparasite. Parasitization in field samples ranged from 30 to 65%. Smalland medium-sized larvae were also infected witha nuclear polyhedrosis virus (NPV); rates ofNPV infection ranged from 0 to 35% in fieldsamples. These results are consistent withanecdotal evidence that natural enemies,primarily generalist predators, are largelyresponsible for maintaining populations ofS. exigua at relatively low levels innontreated sugarbeet fields.     

Comparative effects of gibberellins and an N-substituted phthalimide on seed germination and extension growth of celery (Apium graveolens L.)

The N-substituted phthalimide AC 94377 (1-(3-chlorophthalimido)-cyclohexanecarboxamide) was equally effective as a mixture of the gibberellins A₄ and A₇ (GA_4/7) in breaking dormancy and stimulating germination of celery seeds when either was used in combination with ethephon or daminozide as a seed soak. Whereas seedlings emerging from GA_4/7-treated seeds became etiolated in comparison with those from untreated seeds, those from AC 94377-treated seeds showed normal development. Preharvest sprays of gibberellic acid (GA₃) increased the height of mature plants in comparison with untreated controls by about 16 per cent whereas AC 94377 was ineffective. The yield from GA₃-treated plots was about 10 per cent greater than that from AC 94377-treated plots.     

Evidence for the accumulation of a germination inhibitor during progressive thermoinhibition of seeds of celery (Apium graveolens L.)

The germination of seeds of celery (Apium graveolens L.) becomes progressively thermoinhibited on incubation in the dark at high temperatures, the inhibitory temperature being dependent on the cultivar used. In two high-dormancy cultivars of celery, the production of germination inhibitors in seeds incubated in the dark at 26°C gradually increased over a 7-day period. Inhibitor production was measured by incubating seeds of the low-dormancy cultivar Florida 683 in homogenates of the thermoinhibited seeds of the high-dormancy cultivars and recording germination either in the light or with the gibberellins A₄ and A₇ (GA_4/7) in the dark. Most Florida 683 seeds which failed to germinate in the homogenates after 15 days were induced to germinate by addition of N⁶-benzyladenine (BA). The presence of BA in addition to GA_4/7 throughout incubation in the dark completely overcame the inhibitory effects of homogenates. This indicates that thermoinhibition of celery seeds is associated with the accumulation of a germination inhibitor which interacts with cytokinins. This does not appear to be abscisic acid (ABA) since ABA levels in thermoinhibited seeds were lower than in untreated seeds and did not increase with duration of high temperature treatment.Abbreviations ABA Abscisic acid - BA N⁶-benzyladenine - GA_4/7 a mixture of the gibberellins A₄ and A₇ - HTP high-temperature pretreatment     

不同食物对甜菜夜蛾生长发育参数的影响

选择上海地区近年甜菜夜蛾Spodoptera exigua(Hübner)发生比较严重的甘蓝、豇豆、大葱、芦笋4种寄主植物,在温度(27±1)℃,相对湿度70%±5%,光照L:D=14:10的条件下研究了不同寄主植物对甜菜夜蛾发育特征的影响。结果表明,不同寄主植物饲喂甜菜夜蛾,甜菜夜蛾幼虫发育历期、存活率、蛹重、成虫寿命、净生殖力和内禀增长率等参数在寄主植物间有显著差异。用甘蓝饲喂的甜菜夜蛾雌虫产卵量明显高于取食大葱和芦笋的。同样,取食甘蓝的甜菜夜蛾蛹重、净生殖力和种群内禀增长率等参数明显高于取食大葱和芦笋的,说明甘蓝与其他寄主植物相比提供了较好质量的食物。     

Overwintering and growth regulator treatment effects on celery (Apium graveolens L.) flowering and seed production

Celery (Apium graveolens L.) plants cv. Jason overwintered in a polythene tunnel flowered earlier and grew taller than similar plants given a 10-week cold-treatment at 5°C prior to transplanting in the same tunnel in mid-February. However, there was no significant difference in the yield of seeds obtained from both treatments, plants grown at a density of 4m^-2 yielded less seeds than those at 2m^-2, though the yield per unit area was slightly higher from the high density treatment. Treatment with 100 mgl^-1 GA₃ applied twice just prior to flowering and during anthesis increased flower stalk, flower pedicel and stamen length but delayed flower opening and seed ripening and decreased seed set and seed yield. Treatment with a mixture of 1000 mgl^-1 GA₄ and GA₇ plus 1000 mgl^-1 ethephon on three occasions during seed ripening decreased seed yield and reduced seed germination though those seeds capable of germinating were less dormant than seeds from untreated plants. The size distribution of seeds was unaffected by any treatment other than the preseeding spray with GA₃ which reduced the percentage of medium-size seeds.     

Effect of host plants on the infectivity of nucleopolyhedrovirus to Spodoptera exigua larvae

Previous studies have shown that the infectivity of baculovirus to herbivores is affected by phytochemicals ingested during the acquisition of viral inoculum on the foliage of host plants. Here, we measured the effects of 14 host plant species on the infectivity of Spodoptera exigua nucleopolyhedrovirus (SeNPV) to its larvae. The order of the LD₅₀ values of SeNPV among the host plants was Ipomoea aquatica > Brassica oleracea > Raphanus sativus > Amaranthus tricolor > Spinacia oleracea > Vigna unguiculata > Solanum melongena > Capsicum annuum > Apium graveolens > Allium fistulosum > Lactuca sativa > Brassica chinensis > Zea mays > Glycine max, with 940.1 ± 2.26, 424.0 ± 0.60, 295.2 ± 1.13, 147.3 ± 0.63, 138.6 ± 0.22, 119.9 ± 0.07, 119.8 ± 0.02, 109.2 ± 0.18, 104.8 ± 0.62, 102.1 ± 0.66, 97.9 ± 0.22, 89.9 ± 0.32, 79.0 ± 0.13 and 64.0 ± 0.38 OBs per larva, respectively, and the values of mean time to death of virus‐infected larvae were 6.21 ± 0.11, 7.12 ± 0.10, 7.33 ± 0.21, 6.97 ± 0.02, 7.06 ± 0.01, 7.29 ± 0.03, 7.32 ± 0.05, 7.07 ± 0.08, 7.24 ± 0.11, 7.09 ± 0.13, 7.50 ± 0.06, 7.23 ± 0.01, 7.30 ± 0.02 and 7.19 ± 0.07 days, respectively. The mean time to death of larvae decreased with increasing viral dose, and corrected mortality decreased as the larval mean time to death increased. These findings have significance for understanding the effects of host plants on the infectivity of baculovirus to noctuids.     

Impact of native predators and parasites on Spodoptera exigua, an introduced pest of alfalfa hay in northern California

A long-term study of Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) revealed that a complex of native predators and parasites exploit this introduced pest in alfalfa-hay fields in northern California. In field trials, predators typically fed on >50% of sentinel egg masses during a given sample interval; mean predation rate ranged from 40 to 100% and percentage predation per individual egg mass was density-independent (spatial context) for 16 of 17 sample intervals. The egg-predator guild consisted primarily of adults and nymphs of Lygus hesperus Knight & L. elisus Van Duzee (Miridae), Nabis americoferus Carayon (Nabidae), and Orius tristicolor (White) (Anthocoridae); and adults of Collops vittatus (Say) (Melyridae) and Hippodamia convergens Guerin-Meneville (Coccinellidae). In laboratory feeding trials, these species readily fed on eggs, as well as neonate larvae of S. exigua. The parasite guild associated with small- to medium-sized larvae consisted of Hyposoter exiguae (Viereck) and Pristomerus spinator (F.) (Ichneumonidae), both larval endoparasites; and Chelonus insularis Cresson (Braconidae), an egg-larval endoparasite. Total parasitization by these species in field samples ranged from 5 to 75%, and was density-independent (spatial context) for each of four sample dates. A few larvae were infected with a nuclear polyhedrosis virus but no epizootics were observed. These results are consistent with the hypothesis that native natural enemies, especially generalist predators, can maintain populations of S. exigua at levels well below the treatment threshold for this exotic pest of alfalfa grown for hay.     

Effects of genetic and environmental host plant variation on the susceptibility of two noctuids toBacillus thuringiensis

TwoApium graveolens var.rapaceum (L.) cultivars that differ in their suitability for the survival and growth ofSpodoptera exigua (Hübner) andTrichoplusia ni (Hübner) were used to examine the effect of genetic and seasonal environmental variation in host plant suitability on the efficacy ofBacillus thuringiensis subsp.kurstaki (Berliner). The effects of host plant genotype andB. thuringiensis were generally independent, so thatB. thuringiensis efficacy was greatest on the resistant host plant cultivar. Host plant suitability varied within growing season for both insect species but, while host plant suitability decreased with increasing plant age forT. ni, the response ofS. exigua to plant age was not as clear. Within season variation in host plant suitability affectedB. thuringiensis efficacy and the interaction betweenB. thuringiensis and host plant cultivar forS. exigua but not forT. ni. Soluble protein and Folin-Denis phenolic concentrations of host plant tissue were not correlated with changes in host plant suitability to either insect species.     

Uptake of protoplasts from the filamentous fungiAspergillus nidulans andFusarium oxysporum into protoplasts from celery (Apium graveolens L.)

Summary Protoplasts isolated from celery cell suspension cultures, were mixed with fungal protoplasts, from either the saprophytic speciesAspergillus nidulans or the pathogenic speciesFusarium oxysporum. The incubation of protoplast mixtures with PEG caused close adhesion between plant and fungal protoplasts. Subsequent dilution of PEG resulted in the uptake of protoplasts from either fungal species into the plant protoplast cytoplasm. A range of PEG concentrations, incubation times and dilution rates were tested to maximise adhesion and uptake frequencies. Identification of uptake was achieved either by fluorescent staining of nuclei or by electron-microscopy. A maximum of 10% celery protoplasts had taken upA. nidulans protoplasts after PEG treatment. Fungal protoplasts were taken up into celery protoplast cytoplasm by endocytosis, and were maintained within vesicles; two bounding membranes were observed by electron microscopy. Plant protoplast viability was determined during prolonged incubation following fungal protoplast uptake. The presence ofA. nidulans protoplasts tended to maintain celery protoplast viability and although some morphological disintegration occurred intact celery protoplasts remained for at least 92 h after uptake. The uptake ofF. oxysporum protoplasts markedly depressed celery protoplast viability after 24 h incubation and greater celery protoplast disintegration occurred.Abbreviations PEG Polyethylene glycol - DAPI 4,6-diaminido-2-phenylindole - 2,4-D 2,4-dichlorophenoxyacetic acid     

Gibberellin involvement in dormancy-break and germination of seeds of celery (Apium graveolens L.)

The temperature-dependent, primary dormancy of cv. Florida 683 celery seeds in darkness was partially broken by a 30 min light exposure on the third day of incubation at 20–22°C, resulting in c 50 percent germination after 20 days. This light stimulation was negated by including different inhibitors of gibberellin biosynthesis in the incubation medium. Subsequent addition of a solution of the gibberellins A₄ and A₇ or of the gibberellin-active compound (1-3-chlorophthalimido)-cyclohexane carboxamide (AC94,377) overcame the inhibitory effects on germination of these GA-biosynthesis inhibitors. It is suggested that light stimulates the biosynthesis of gibberellins which are essential for dormancy-break in celery seeds and that this biosynthesis is either directly or indirectly controlled through phytochrome.Abbreviations AC94,377 1-(3-chlorophthalimido)-cyclohexane carboxamide; ancymidol, -cyclopropyl--(4-methoxyphenyl)-5-pyrimidinemethanol - AMO1618 N,N,N-2-tetramethyl-5-(1-methyl ethyl)-4-(1-piperidinylcarbonyl)oxy-benzenaminium chloride - BTS44584 S-2,5-dimethyl-4-pentamethylenecarbamoyloxyphenyl-SS-dimethyl sulphonium - P toluenesulphonate; chlormequat chloride, 2-chloroethyltrimethylammonium chloride; daminozide - N dimethylaminoscuccinamic acid; paclobutrazol, (2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl pentan-3-ol)     

寄主植物对甜菜夜蛾三龄幼虫抗寒力的影响

寄主植物是影响昆虫抗寒性的主要因子之一。研究了不同温度下甜菜夜蛾Spodoptera exigua(Hübner)3龄幼虫取食小白菜、甘蓝、葱和菠菜后,对过冷却能力和体内冷冻保护剂的影响。结果表明,寄主植物对甜菜夜蛾3龄幼虫的过冷却能力有显著性影响,其中以取食甘蓝的幼虫过冷却点最低。温度和寄主植物对其过冷却点、结冰点和虫体含水量有明显的交互作用。寄主植物对其体内的海藻糖含量有显著性影响,而对甘油和糖原含量没有显著性影响。温度和寄主植物仅对海藻糖含量有显著的交互作用。随着温度的升高,取食不同寄主的幼虫体内海藻糖和糖原含量的变化趋势完全相反,认为海藻糖是由糖原转化而来。研究结果提示冬季合适的寄主植物有利于甜菜夜蛾低龄幼虫越冬。     

Possible control of gibberellin-induced release of temperature-dependent primary dormancy in seeds of celery (Apium graveolens L.) by transmembrane ion fluxes

The temperature-dependent primary dormancy of cv Florida 683 celery seeds in darkness was broken by GA_4/7 (2 × 10^-4 M) alone but other growth regulators such as BA, ethephon or daminozide were necessary to break dormancy of cv Lathom Blanching seeds in the presence of GA_4/7 at this concentration. Although AgNO₃ partially inhibited both the ethephon- and BA- induced germination of cv Lathom Blanching seeds in the presence of GA_4/7 in the dark it did not affect the promotive action of daminozide. Ethephon did not overcome the inhibitory action of high concentrations of AgNO₃ in the light. The ethylene synthesis inhibitor aminoethoxyvinylglycine (AVG) did not inhibit the germination of cv Lathom Blanching seeds induced by growth regulators in the dark or in the absence of growth regulators in the light. Fusicoccin (FC) did not break celery seed dormancy unless applied in the presence of GA_4/7. Germination of cv Lathom Blanching celery seeds treated with GA_4/7 at 16°C in the dark was inhibited by the K⁺ ionophore benzo-18-crown-C-6 (18-C-6) and in the presence of Ca²⁺ by the Ca²⁺ ionophore A23187; the 18-C-6 inhibition was reversed by BA.It is concluded that the involvement of gibberellin in celery seed dormancy is not dependent on endogenous ethylene and is directly or indirectly controlled through the action of other hormones on transmembrane ion fluxes.     

Somaclonal variant UC-T3: the expression of Fusarium wilt resistance in progeny arrays of celery,Apium graveolens L.

Summary First generation (S₁) progeny, second generation (S₂) progeny, and backcross (BC) progeny of a celery (Apium graveolens L. var. dulce) somaclonal variant, UC-T3, were evaluated for resistance to the fungus Fusarium oxysporum f. sp. apii, race 2 (FOA₂). Chisquare analysis of S₁ progeny showed that the expression of resistance did not fit a single-locus model. S₂ progeny means were similar among families, except in a heavily infested field. The lowest ranking S₂ family in both the lightly infested and heavily infested fields was significantly more resistant to FOA₂ than individuals of the susceptible progenitor line Tall-Utah 527OR; therefore; it was concluded that the trait was heritable. The phenotypic distribution of the backcross progeny was broad, suggesting that the new resistance was conferred by at least two genes whose expression was dominant to susceptibility. The mean scores for disease resistance of the progeny of crosses between UC-T3 and the moderately resistant line, Tall-Utah 527OHK, generally equaled the resistance found among the progeny of the most resistant parent.     

RNA interference of an antimicrobial peptide, gloverin, of the beet armyworm, Spodoptera exigua, enhances susceptibility to Bacillus thuringiensis

Gloverin is known to be an inducible antimicrobial peptide. This study reports a gloverin gene (Seglv) identified from the beet armyworm, Spodoptera exigua. Seglv encodes 175 amino acids with a signal peptide. Its amino acid sequence is highly homologous (>95%) to other known gloverins. Seglv was expressed from egg to adult stages even without immune challenge. Especially, in larval stage, it was expressed in all tested tissues, such as hemocyte, fat body, gut, and epidermis. However, the constitutive expression level was significantly elevated in response to bacterial challenge. Expression of a Toll gene was required for expression of Seglv. A recombinant Seglv protein was synthesized using a bacterial expression system and purified with an affinity chromatography. The recombinant protein showed a specific antibacterial activity against a Gram-positive bacterium, but no activity against a Gram-negative Escherichia coli. Injection of specific double stranded RNA (dsRNA) against Seglv could suppress its expression. Knockdown of Seglv expression induced a significant developmental retardation and resulted in hypotrophy pupae. The larvae treated with dsRNA were much more susceptible to Bacillus thuringiensis than the control larvae. These results suggest that Seglv acts as an antimicrobial peptide especially against Gram-positive bacteria including B. thuringiensis.