A Proposed Role for the Cuticular Fatty Amides of Liposcelis bostrychophila (Psocoptera: Liposcelidae) in Preventing Adhesion of Entomopathogenic Fungi with Dry-conidia

Maximum challenge exposure of Liposcelis bostrychophila to Beauveria bassiana, Paecilomyces fumosoroseus, Aspergillus parasiticus or Metarhizium anisopliae resulted in no more than 16% mortality. We investigated several of L. bostrychophila's cuticular lipids for possible contributions to its tolerance for entomopathogenic fungi. Saturated C14 and C16 fatty acids did not reduce the germination rates of B. bassiana or M. anisopliae conidia. Saturated C6 to C12 fatty acids that have not been identified in L. bostrychophila cuticular extracts significantly reduced germination, but the reduction was mitigated by the presence of stearamide. Cis-6-hexadecenal did not affect germination rates. Mycelial growth of either fungal species did not occur in the presence of caprylic acid, was reduced by the presence of lauric acid, and was not significantly affected by palmitic acid. Liposcelis bostrychophila is the only insect for which fatty acid amides have been identified as cuticular components. Stearamide, its major fatty amide, did not reduce germination of B. bassiana or M. anisopliae conidia or growth of their mycelia. Adhesion of conidia to stearamide preparations did not differ significantly from adhesion to the cuticle of L. bostrychophila. Pretreatment of a beetle known to be fungus-susceptible, larval Oryzaephilus surinamensis, with stearamide significantly decreased adhesion of B. bassiana or M. anisopliae conidia to their cuticles. This evidence indicates that cuticular fatty amides may contribute to L. bostrychophila's tolerance for entomopathogenic fungi by decreasing hydrophobicity and static charge, thereby reducing conidial adhesion.     

Leaf and root extracts of the invasive shrub, Lonicera maackii, inhibit seed germination of three herbs with no autotoxic effects

In addition to effects mediated by resource competition, some invasive plants may impact surrounding vegetation by secreting compounds that are directly inhibitory to growth. Lonicera maackii, an invasive Asian shrub of forests and open areas in eastern and midwestern North America, has devastating effects on understory vegetation, some of which persist even after this shrub is removed. In this study, we explored the potential of aqueous extracts of the leaves and roots of this plant to inhibit seed germination of Impatiens capensis, Alliaria petiolata, Arabidopsis thaliana, and L. maackii in Petri dish bioassays. Both L. maackii root and leaf extracts significantly decreased germination in the three herb species. This inhibitory effect generally increased with increasing extract concentration and was more pronounced with application of leaf extract than root extract. However, when the same extracts were applied to seeds of L. maackii itself, germination was delayed in some cases, but was not significantly reduced by the end of the experiment. Germination of L. maackii seeds even reached significantly higher levels in some extract treatments than in no-extract controls. This implies that L. maackii can successfully inhibit the germination of other plants with few autotoxic effects and may even promote the germination of its own seeds.     

Effects of water extracts of a composted manure-straw mixture on the plant pathogen Botrytis cinerea

Manure-straw mixtures were composted and water extracts, made by incubating compost in water for 3 to 18 days, were assessed for antagonistic activity against Botrytis cinerea, using a range of tests. Extracts of all ages inhibited conidial germination on glass slides and reduced mycelial growth on agar. Mixing extracts of all ages with droplets of suspensions of B. cinerea conidia on detached Phaseolus bean leaves suppressed lesion development, but only 3- to 8-day-old extracts had an effect when sprayed onto leaves 2 days before inoculation. Extracts contained a large and varied microbial population of actinomycetes (0.3 to 2.4×10⁵ c.f.u.ml^–1), bacteria (1.5 to 5.6×10¹⁰ c.f.u.ml^–1), filamentous fungi (25.0 to 45.5 c.f.u. ml^–1) and yeasts (26.1 to 62.6 c.f.u.ml^–1). Eight- and 18-day-old extracts lost activity completely on filter sterilization or autoclaving. Weekly sprays of 8-day-old extracts onto lettuce in the glasshouse had no effect on the incidence of grey mould, but significantly reduced its severity and increased marketable yield. The use of compost extracts in biocontrol of plant diseases and their possible mode of action is discussed.M.P. McQuilken and J.M. Whipps are and J.M. Lynch was with the Microbiology and Crop Protection Department, Horticulture Research International, Littlehampton BN17 6LP, UK; J.M. Lynch is now with the School of Biological Sciences, University of Surrey, Guildford GU2 5XH, UK.     

Two sides of a leaf blade: <Emphasis Type="Italic">Blumeria graminis</Emphasis> needs chemical cues in cuticular waxes of <Emphasis Type="Italic">Lolium perenne</Emphasis> for germination and differentiation

Plant surface characteristics were repeatedly shown to play a pivotal role in plant–pathogen interactions. The abaxial leaf surface of perennial ryegrass (Lolium perenne) is extremely glossy and wettable compared to the glaucous and more hydrophobic adaxial surface. Earlier investigations have demonstrated that the abaxial leaf surface was rarely infected by powdery mildew (Blumeria graminis), even when the adaxial surface was densely colonized. This led to the assumption that components of the abaxial epicuticular leaf wax might contribute to the observed impairment of growth and development of B. graminis conidia on abaxial surfaces of L. perenne. To re-assess this hypothesis, we analyzed abundance and chemical composition of L. perenne ab- and adaxial epicuticular wax fractions. While the adaxial epicuticular waxes were dominated by primary alcohols and esters, the abaxial fraction was mainly composed of n-alkanes and aldehydes. However, the major germination and differentiation inducing compound, the C₂₆-aldehyde n-hexacosanal, was not present in the abaxial epicuticular waxes. Spiking of isolated abaxial epicuticular Lolium waxes with synthetically produced n-hexacosanal allowed reconstituting germination and differentiation rates of B. graminis in an in vitro germination assay using wax-coated glass slides. Hence, the absence of the C₂₆-aldehyde from the abaxial surface in combination with a distinctly reduced surface hydrophobicity appears to be primarily responsible for the failure of normal germling development of B. graminis on the abaxial leaf surfaces of L. perenne.     

Allelopathic effect of common weeds on soybean growth and soybean-Bradyrhizobium symbiosis

Water extracts of shoot of common lambsquarters (Chenopodium album), yellow nutsedge (Cyperus esculentus) and sunflower (Helianthus annuus) at 1% level significantly reduced soybean seed germination. Soybean seedlings inoculated with broth culture of nodule bacterium were grown for 25 days in N-free nutrient solution amended with cold water extracts of weed residues at 1 and 2% levels. At both levels extracts from residues of all weeds except that of lambsquarters enhanced growth of soybean. Nodulation was generally stimulated by the extracts of five weeds at 1% level except that of lambsquarters. Extracts from lambsquarters at 2% level completely suppressed and at 1% level reduced nodulation by 60%. Extracts from green foxtail (Setaria viridis), Pennsylvania smartweed (Polygonium pensylvanicum) and sunflower at 2% level reduced and at 1% level enhanced nodulation. The residues of lambsquarters shoot incorporated with soil at 0.5 and 1% levels caused 85 and 96% reduction respectively in seed germination and those of Pennsylvania smartweed and sunflower at 1% reduced seed germination by 40–70% but not at 0.5% level. The residues of foxtail and smartweed at both levels enhanced growth and nodulation. Under similar conditions nutsedge at 1% level stimulated nodulation but not growth. The residues of lambsquarters at both levels were inhibitory to nodulation but stimulated growth at 0.5% level.     

Development of natto with germination-defective mutants of <Emphasis Type="Italic">Bacillus subtilis</Emphasis> (<Emphasis Type="Italic">natto</Emphasis>)

The effects of cortex-lysis related genes with the pdaA, sleB, and cwlD mutations of Bacillus subtilis (natto) NAFM5 on sporulation and germination were investigated. Single or double mutations did not prevent normal sporulation, but did affect germination. Germination was severely inhibited by the double mutation of sleB and cwlD. The quality of natto made with the sleB cwlD double mutant was tested, and the amounts of glutamic acid and ammonia were very similar to those in the wild type. The possibility of industrial development of natto containing a reduced number of viable spores is presented.     

Seed germination of three species of <Emphasis Type="Italic">Vallisneria</Emphasis> (Hydrocharitaceae), and the effects of freshwater microalgae

Two experiments were conducted to investigate seed germination under natural temperature and light regimes and to evaluate the influence of freshwater microalgae on seed germination of threeVallisneria species. Seeds exposed to natural seasonal temperature and light changes for 24 months germinated only in spring, perhaps indicating an annual dormancy/non-dormancy cycle. The ecological background of the natural habitat seems to play predominant roles in seed germinability. Mean cumulative seed germination percentages of Vallisneria natans, V. denseserrulata, andV.spinulosa of the first year were 35.2, 19.2, and 11.2%, respectively, and of the second year were 80, 72, and 32.4%, respectively. Germination rates differed significantly among the three Vallisneria species exposed to natural seasonal temperature and light changes in the first year, but differed only between Vallisneria spinulosa and the other two species in the second year. The differences of germination may influence the geographical distribution and thus be related to different survival strategies of the species. Seed germination rates in culture solution inoculated with algae were significantly higher than in solution with no algae. A strong correlation occurred between total biomass of freshwater microalgae and seed germination of the three studied species. Apparently, the extracellular products of freshwater microalgae may play an important role in seed germination. These results support the hypothesis that Vallisneria colonization may be mediated by algae facilitation.     

Cuticular Extracts of Five Common Mantids (Mantodea: Mantidae) of the Eastern United States

We undertook a preliminary investigation of the cuticular extracts of five common mantid species in the eastern United States: Tenodera sinensis (Saussure), T. angustipennis (Saussure) and Mantis religiosa (Linnaeus) introduced from the Old World and Stagmomantis carolina (Johannson) and Bruneria borealis (Scudder), which are New World species. The major components of these mixtures were normal alkanes, predominately hentriacontane, or in the case of the parthenogenic species B. borealis, tritriacontane. Tricontanal was detected in the extracts of all five species, and smaller amounts of other aldehydes and n-tricontanol were detected in some species. Complex mixtures of methyl and dimethylalkanes also were present in these extracts. The composition of the cuticular hydrocarbons of these mantids may be an adaptation for reduction of evaporative water loss in these insects that inhabit open fields.     

Cuticular and non-cuticular substrate influence on expression of cuticle-degrading enzymes from conidia of an entomopathogenic fungus,Nomuraea rileyi

Larval cuticle fromTrichoplusia ni, Helicoverpa (=Heliothis)zea, andHeliothis virescens and a cellulose substrate were used to quantify release of proteolytic, chitinolytic, and lipolytic enzymes by germinating conidia of the entomopathogenic fungus,Nomuraea rileyi. There was no significant difference in conidial viability incubated withT. ni, H. zea or cellulose substrates. Conidial viability onH. virescens cuticle, however, was significantly lower (ca. 19–25%) than the other three substrates. The presence of cuticle substrates, especially cuticle ofT. ni, stimulated germination. The nature of the substrate influenced both the time and quantity of the enzymes expressed. Specific proteases (aminopeptidase, chymoelastase, trypsin) generally were expressed earlier and/or in greater quantities on cuticular than on the cellulose substrate. Although both chitinolytic enzymes (endochitinase, N-acetylglucosaminidase) were detected on all three cuticular substrates, their activity was substantially lower than that of the proteolytic enzymes. Lipase activity was only minimally present. Early concurrent release of both proteases and chitinases suggested that both may be important in the penetration of the larval integument by germinating conidia ofN. rileyi. Expression of proteases and chitinases, especially aminopeptidase and endochitinase was probably a specific response to cuticle, because little or no activity was expressed on the non-host, cellulose substrate.This article reports the results of research only. Mention of a proprietary product in this paper does not constitute a recommendation for use by the US Department of Agriculture.     

Protection of entomopathogenic conidia against chemical fungicides afforded by an oil-based formulation

We evaluated the protection afforded by an oil formulation against non-compatible fungicides in mixtures with conidia of the entomopathogenic fungi Metarhizium anisopliae (Ma) and Beauveria bassiana (Bb). Under laboratory conditions, viability of unformulated (aqueous suspensions) Ma conidia was harmed by recommended label doses of carbendazim (not tested for Bb), and both Ma and Bb conidia were affected by triadimefon. On the other hand, effect of fungicides was usually nil or minimal on conidia formulated as oil-containing suspensions (emulsifiable oil + water). Germination rates for unformulated and oil-formulated Ma conidia subjected to carbendazim were reduced by 77.3 and 12.1%, respectively, compared to their fungicide-free counterparts. Germination rates at 16 h post-inoculation for unformulated and oil-formulated Bb conidia subjected to triadimefon were reduced by 20.5 and 5.5%, respectively, compared to their fungicide-free counterparts. No differences were observed at 20 h post inoculation, indicating a fungistatic action of this compound on Bb conidia. Virulence of unformulated conidia amended with fungicides against third instar Diatraea saccharalis larvae was negatively affected compared to their formulated counterparts. These results suggest that oil-formulated conidia can be effectively protected from damage caused by chemicals, which could have applications in tank mixing or alternate applications with shared spraying equipment, being especially relevant for IPM programs in which mycopesticides and chemicals are simultaneously sprayed.     

Substrate influence on physiology and virulence of <Emphasis Type="Italic">Beauveria bassiana</Emphasis> acting on larvae and adults of <Emphasis Type="Italic">Tenebrio molitor</Emphasis>

Two isolates of Beauveria bassiana, wild type (wt) and its mutant type (mt) were compared in terms of growth patterns on culture plates containing media based on wheat bran, grasshopper exoskeletons, colloidal chitin or Sabouraud-dextrose agar (SDA). Germination for the mt isolate was up to 33% faster in all media. Influence of media on virulence was determined against larvae and adults of Tenebrio molitor. Mortality higher than 90% was reached for adults after 6 days using conidia from all media. For larvae, a mortality of 80% was reached after 11 days with conidia collected from SDA medium and between 15 and 35% with conidia from other media. In SDA medium, conidial yield was almost ten times higher for the mt isolate compared to the wt isolate; however, virulence traits were similar against either larvae or adults. These results may influence commercial preparations of entomopathogenic fungi based on conidia.     

Selective inhibitors of germination of legume seeds in activated sludge compost

Water extracts of the compost produced from activated sludge and coffee residue were found to be selectively inhibitory to seed germination of some legumes. Germination rate of white clover (Trifolium repens L.), red clover (Trifolium pratense L.) and alfalfa (Medicago sativa L.) seeds were reduced to 2, 29 and 73% of the control, respectively, by water extracts of the compost (20 g l^–1). However, the extracts did not show any inhibition to seed germination of sorghum (Sorghum bicolor Moench), African millet (Eleusine coracana Gaertn.), and Komatsuna (Brassica rapa L.) at the same concentration. The inhibitors in the compost extracts were separated by ion-exchange chromatography and reverse-phase high performance liquid chromatography (HPLC) and the inhibitory activities of seed germination were tested with white clover seeds. Five inhibitors were isolated and identified as 3,4-dichlorophenylacetic acid (3,4-DCP), 3,4-dichlorobenzoic acid (3,4-DCB), 3,4,5-trichlorophenylacetic acid, 3,4,5-trichlorobenzoic acid and mono-2-ethylhexylphthalate by ¹H-, ¹³C-NMR spectroscopy and mass spectrometry. The inhibitory activities of some authentic chemicals of the inhibitors and the related compounds were compared. The results indicated that the main inhibitor in the compost could be 3,4-DCB, which was contained at the concentration of 6.58 mg kg^–1 compost and showed the strongest inhibitory effect on seed germination of white clover among the tested compounds.     

Losing the battle against fungal infection: suppression of termite immune defenses during mycosis

The dampwood termite, Zootermopsis angusticollis is known to generate humoral immune responses to the entomopathogenic fungus Metarhizium anisopliae. However, little is known about how the termite's cellular immune system reacts to fungal infection. To test the effect of conidia exposure on cellular immunity, we quantified the number and types of hemocytes in the hemolymph of naïve nymphs and compared their circulating counts with those of nestmates exposed to 0, 2 × 10³, 2 × 10⁶ or 2 × 10⁸ conidia/ml doses. These termites were then bled and their hemocytes counted on days 1, 2, 3, 4, 7 post-exposure. Our results show, first, that naïve Z. angusticollis nymphs have three different blood cell types tentatively identified as granular hemocytes, prohemocytes and plasmatocytes. In these individuals, plasmatocytes were on average 13.5 and 3.3 times more numerous than granular hemocytes and prohemocytes, respectively. Second, a full factorial general linear analysis indicated that hemocyte type, time elapsed since conidia exposure and conidia dosage as well as all their interactions explained 43% of the variability in hemocyte density. The numbers of prohemocytes and particularly plasmatocytes, but not granular hemocytes, appear to be affected by the progression of disease. The decline in hemocyte numbers coincided with the appearance of hyphal bodies and the onset of “sluggish” termite behavior that culminated in the insect's death. Hemocyte counts of infected males and females were affected to the same extent. Hence, M. anisopliae overtakes the cellular immune responses of Z. angusticollis mainly by destroying the host's most abundant hemocyte types.     

Botrytis cinerea: Activité Antifongique dans les Jeunes Grappes de Vitis vinifera, Varieté Gamay

Botrytis cinerea: fungicidal activity in young grape berries of Vitis vinifera (Gamay) Extracts of young grape berries of Vitis vinifera (Gamay) inhibit the germination of conidia of Botrytis cinerea. This inhibitory activity is present in extracts obtained from clusters at bloom stage and is maintained until a developmental stage close to the maturity. These extracts ruptured the cellular membranes.     

Changes in composition of phenolic compounds and antioxidant properties of <Emphasis Type="Italic">Vitis amurensis</Emphasis> seeds germinated under osmotic stress

The research focused on the changes of phenolic compounds as well as their antiradical activity and reducing power isolated from Amur grape (Vitis amurensis) seeds during germination under optimal conditions and under osmotic stress. The seeds were found to contain tannins, (+) catechin, (−) epicatechin, and gallic acid (in free, ester- and glycoside-bound forms). Extracts from the seeds were also shown to contain two other phenolic acids: caffeic and p-coumaric acids, in very low levels. During a 3-day seed germination test under osmotic stress (−0.5 MPa), the content of total phenolics, tannins and phenolic acids declined as compared to the control. However, seed germination under stress conditions led to a significant increase in the amount of catechins. Because catechin is the one of the units in condensed tannins, its dynamic increase during seed germination may be involved in metabolism of tannins under osmotic stress. It is also likely that the synthesis of catechins is greater under stress conditions and these compounds may be engaged in the process of acclimatization of grapevines to stress conditions. The content of total phenolic compounds in seed extracts is positively correlated with their antioxidant properties. The extracts from seeds germinated under optimal conditions exhibited strong antiradical properties against the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical as well as reducing power. As regards the extracts from grape seeds germinated under osmotic stress, this capability was much weaker. The research demonstrated that antioxidants could interfere with the oxidation process induced by various stresses by acting as oxygen scavengers, therefore the tolerance to drought stress might be correlated with an increase in the antioxidant potential.     

Effects of cuticle source and concentration on germination of conidia of two isolates of Nomuraea rileyi

The effects of cuticle from larvae of Trichoplusia ni, Heliothis zea and H. virescens on rate and extent of germination of conidia of a Mississippian isolate (MS) and an Ecuadoran (EC) isolate of Nomuraea rileyi were studied. Solid substrates generally stimulated more germination than submerged substrates. There was little or no effect of cuticle source (H. zea or H. virescens) on germination of either the EC isolate or the MS isolate cultured on a solid substrate, however, differences in patterns of germination were obtained in submerged substrates. Addition of cuticle of H. zea or H. virescens generally increased the germination time for the MS isolate. Germination time for the EC isolate was significantly increased when H. virescens cuticle was used.This article reports the results of research only. Mention of a proprietary product in this paper does not constitute a recommendation for use by U.S. Department of Agriculture.     

黄土丘陵区草本群落演替中先锋种群茵陈蒿浸提液的化感作用

为探索自然演替中植被群落结构与化感作用之间的关系,以黄土丘陵区自然演替中先锋种群茵陈蒿为研究对象,通过种子萌发试验,分析演替初期优势种群茵陈蒿浸提液(甲醇浸提液和水浸提液)对自身以及伴生种种子萌发以及幼苗生长的影响,从化学生态学角度解释演替初期群落结构形成的原因。结果表明,茵陈蒿浸提液对3种伴生种(铁杆蒿、白羊草和达乌里胡枝子)的种子萌发均有显著化感作用,低浓度(0.002g/m L)时表现为促进或轻微的抑制作用,高浓度(0.2g/m L)时为较强的抑制作用;不同部位茵陈蒿浸提液的化感作用不同,相比之下,地上部的抑制作用更为强烈,其浸提液均抑制铁杆蒿、白羊草和达乌里胡枝子的种子萌发,尤其在浓度为0.2 g/m L时,达到完全抑制;根系甲醇浸提液对铁杆蒿种子萌发的抑制作用要强于同浓度下的水浸提液,而地上部水浸提液对受体植物根芽的作用大于甲醇浸提液。茵陈蒿对于自身具有一定的抑制作用,表现为高浓度(0.2和0.02 g/m L)的水和甲醇浸提液抑制自身种子萌发和幼苗生长。研究结果说明化感作用可能是该地区在演替前期形成以茵陈蒿为优势种植被群落的重要原因之一。创新点:从化学生态学的角度解释了黄土丘陵区植被演替初期植物之间的关系以及群落结构形成的原因,为认识自然恢复的内在机理提供了新的视角。     

In vitro fungitoxicity of the essential oil of Syzygium aromaticum

The in vitro antifungal activity of clove oil was studied against four test fungi namely Alternaria alternata, Fusarium chlamydosporum, Helminthosporum oryzae and Rhizoctonia bataticola by the agar well diffusion method. These test fungi were found to be highly sensitive to clove oil at a concentration of 100 μl/well. The inhibition zone diameter was found to be in the range of 55–65 mm. The toxicity of clove oil on the germination and growth of A. alternata was further examined in liquid medium. Concentration- and time-dependent toxicity was recorded from 0.05 to 20% (v/v) concentration. The minimum fungistatic concentration was found to be 0.05%. Above this concentration, lysis of conidia and inhibition of mycelial growth were detected. Microscopic analysis showed 20–40% lysis of conidia after 72 h of incubation at 5% concentration. However at higher clove oil concentration (10%), up to 20% of conidia were lysed within 24 h of incubation. Similar concentration- and time-dependent toxicity was observed at different concentrations and time intervals. The findings indicated that clove oil possesses fungicidal activity against phytopathogenic fungi. Further study is required to determine whether it could have value in the management of plant infectious diseases. This revised version was published online in July 2006 with corrections to the Cover Date.     

A direct observation technique for evaluating sclerotium germination by Macrophomina phaseolina and effects of biocontrol materials on survival of sclerotia in soil

Germination of sclerotia of Macrophomina phaseolina was quantified by direct microscopic observation following application of experimental treatments in vitro and incubation of sclerotia in soil. To assay germination, pieces of agar containing sclerotia were macerated in dilute, liquid cornmeal agar on glass slides; thinly spread; and incubated in a saturated atmosphere for 18–22 h. Germinated sclerotia then were identified by morphological features of germ hyphae. Frequencies of germination were similar in three dilute agar media. Germination was not affected by air-drying sclerotia for 2 weeks, but it was significantly reduced after 4 weeks and greatly reduced or eliminated after 6 or 8 weeks. Survival of sclerotia for 14 days in soil was greatest at 50, 75, and 100% moisture-holding capacity, less at 0 and 25%, and least at 125% (flooded soil). Incorporation of ground poultry litter into soil at 5% by weight reduced survival of sclerotia after 13 days, and incorporation of litter at 10% nearly eliminated it. These results indicate that the direct-observation technique may be used to evaluate animal wastes and other agricultural byproducts for biocontrol activity against sclerotia of M. phaseolina in soil.