Extract of Hedera helix induces resistance on apple rootstock M26 similar to Acibenzolar-S-methyl against Fire Blight (Erwinia amylovora)

The potential of acibenzolar-S-methyl (Benzo [1,2,3]thiadiazole-7-carbothioic acid-S-methyl ester, ASM; Bion 50 WG) and of an extract of Hedera helix, to protect M26 apple rootstocks against fire blight was determined under controlled conditions. Marked differences were observed in the rate and extent of multiplication as well as in pathogen cell viability between control and ASM and H. helix-treated rootstocks. Although the pathogen multiplied abundantly in the plant tissue of water-treated rootstocks and showed severe damage, ASM and the plant extract of H. helix applied prior to inoculation with the causal agent of fire blight, E. amylovora (strain 7/74), suppressed disease development and bacterial multiplication. Physiological observations of ASM and plant extract-treated rootstocks indicated that restriction of pathogen colonization in plant tissue was correlated with a pronounced increase of peroxidase (POX) and chitinase activity. Furthermore, physiological changes caused by these treatments in host cells were characterized by POX labeling methods with SDS-Page electrophoresis. Differences in expression of the POX and protein bands were observed in tissues of plants treated with different inducers. POX activity was determined by the presence of three strong bands in plant extract-treated leaves, two strong bands and one very weak band of about 20.1 and 43 kDa were visible in ASM-treated leaves. Evidence is provided that ASM, as well as extract of H. helix are equally capable of inducing of resistance responses in M26 apple rootstock, which result in an increased resistance to E. amylovora—the fire blight pathogen. These findings demonstrate that both treatments have the ability to induce the activation of defense genes leading to the accumulation of structural and biochemical activities at strategic sites, and these can be associated with induction of resistance against fire-blight.     

Induction of an antioxidant enzyme system and other oxidative stress markers associated with compatible and incompatible interactions between chickpea (Cicer arietinum L.) and Fusarium oxysporum f. sp.ciceris

To ascertain if active oxygen species play a role in fusarium wilt of chickpea caused by Fusarium oxysporum f. sp. ciceris, the degree of lipid peroxidation (malondialdehyde formation) and the activity levels of diamine oxidase (DAO), an apoplastic H₂O₂-forming oxidase, and several antioxidant enzymes, namely ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), guaiacol-dependent peroxidase (GPX) and superoxide dismutase (SOD), were determined spectrophotometrically in roots and stems of ‘WR315’ (resistant) and ‘JG62’ (susceptible) chickpea cultivars inoculated with the highly virulent race 5 of the pathogen. Moreover, APX, CAT, GPX and SOD were also analysed in roots and stems by gel electrophoresis and activity staining; and the protein levels of APX and SOD in roots were determined by Western blotting. In roots, infection by the pathogen increased lipid peroxidation and CAT and SOD activities, although such responses occurred earlier in the incompatible compared with the compatible interactions. APX, GPX and GR activities were also increased in infected roots, but only in the compatible interaction. In stems, infection by the pathogen increased lipid peroxidation and APX, CAT, SOD and GPX activities only in the compatible interaction, and DAO activity only in the incompatible one. In general, electrophoregrams agreed with the activity levels determined spectrophotometrically and did not reveal any differences in isoenzyme patterns between cultivars or between infected and non-infected plants. Further, Western blots revealed an increase in the root protein levels of APX in the compatible interaction and in those of SOD in both compatible and incompatible interactions. In conclusion, whereas enhanced DAO activity in stems, and earlier increases in lipid peroxidation and CAT and SOD activities in roots, can be associated with resistance to fusarium wilt in chickpea, the induction of the latter three parameters in roots and stems along with that of APX, GR (only in roots) and GPX (only in stems) activities are rather more associated with the establishment of the compatible interaction.     

Salicylic acid alleviates growth inhibition and oxidative stress caused by zucchini yellow mosaic virus infection in Cucurbita pepo leaves

The effects of zucchini yellow mosaic virus (ZYMV) infection and pretreatments with salicylic acid (SA) on biomass accumulation of pumpkin (Cucurbita pepo cv. Eskandarani) were investigated. The response of photosynthesis, transpiration and the activities of antioxidant enzymes in leaves was also considered. Significant reductions in growth parameters (i.e. leaf area, biomass and shoot height), photosynthesis and chlorophyll a and b content were detected in ZYMV-infected leaves in comparison to healthy controls. Antioxidant enzyme activities were increased up to 3-fold for peroxidase (POD), 2-fold for ascorbate peroxidase (APX) and catalase (CAT) activities and 1.3-fold for SOD activity by virus infection. ZYMV infection also caused increases in H₂O₂ and malondialdehyde (MDA) contents. These results suggest that ZYMV infection causes oxidative stress in pumpkin leaves leading to the development of epidemiological symptoms. Interestingly, spraying pumpkin leaves with SA led to recovery from the undesirable effects of ZYMV infection. Leaves treated with 100 μM SA three days before inoculation had the appearance of healthy leaves. No distinct disease symptoms were observed on the leaves treated with 100 μM SA followed by inoculation with ZYMV. In non-infected plants, SA application increased activities of POD and superoxide dismutase (SOD) and inhibited APX and CAT activities.In contrast, SA treatment followed by ZYMV inoculation stimulated SOD activity and inhibited activities of POD, APX and CAT. In addition, MDA displayed an inverse relation, indicating inhibition of lipid peroxidation in cells under SA treatment. It is suggested that the role of SA in inducing plant defense mechanisms against ZYMV infection might have occurred through the SA-antioxidant system. Such interference might occur through inhibition or activation of some antioxidant enzymes, reduction of lipid peroxidation and induction of H₂O₂ accumulation following SA application.     

The effect of silicon on antioxidant metabolism of wheat leaves infected by Pyricularia oryzae

This study investigated whether the increase in wheat resistance to blast, caused by Pyricularia oryzae, potentiated by silicon (Si) is linked to changes in the activity of antioxidative enzymes. Wheat plants (cv. BR 18) were grown in hydroponic culture with either 0 (–Si) or 2 mm (+Si) Si and half of the plants in each group were inoculated with P. oryzae. Blast severity in the +Si plants was 70% lower compared to the ?Si plants at 96 h after inoculation (hai). Superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX) and glutathione‐S‐transferase (GST) activities were higher in the leaves of the ?Si plants compared with the +Si plants at 96 hai. This indicates that other mechanisms may have limited P. oryzae infection in the +Si plants restricting the generation of reactive oxygen species, obviating the need for increased antioxidative enzyme activity. In contrast, glutathione reductase (GR) activity at 96 hai was higher in the +Si plants than in the ?Si plants. Although the inoculated plants showed significantly higher concentration of malondialdehyde (MDA) than the non‐inoculated plants, lower MDA concentrations were observed in the +Si plants compared with the ?Si plants. The lower MDA concentration associated with decreased activities of SOD, CAT, POX, APX and GST, suggest that the amount of reactive oxygen species was lower in the +Si plants. However, GR appears to play a pivotal role in limiting oxidative stress caused by P. oryzae infection in +Si plants.     

Induction of Systemic Acquired Resistance in Pepper Plants by Acibenzolar-S-methyl against Bacterial Spot Disease

The ability of acibenzolar-S-methyl to induce resistance in pepper plants against Xanthomonas campestris pv. vesicatoria was investigated in both growth chamber and open field conditions. Growth chamber experiments showed that acibenzolar-S-methyl (300M) treatment protects pepper plants systemically and locally against X. campestris pv. vesicatoria. Evidence for this was a reduction in the number and diameter of bacterial spots and bacterial growth in planta. Systemic protection was also exerted by the acibenzolar-S-methyl acid derivative, CGA 210007, which may be produced by hydrolysis in the plant. The efficacy of acibenzolar-S-methyl was also found in open field conditions, where both leaves and fruit were protected from the disease. The highest efficacy (about 67%) was obtained by spraying the plants 6–7 times every 8–12 days with a mixture of acibenzolar-S-methyl and copper hydroxide (2.5 + 40ghl^–1 active ingredient). Persistence and translocation data obtained from the growth chamber experiments revealed a persistence of acibenzolar-S-methyl lasting five days after treatment with rapid translocation and negligible levels of acid derivative formation. Since the protection exerted by acibenzolar-S-methyl against bacterial spot disease was observed when the inducer was completely degraded, it would appear to be due to SAR activation.     

Phyllosphere yeasts antagonize penetration from appressoria and subsequent infection of maize leaves by Colletotrichum graminicola

In growth cabinet experiments, the common phyllosphere yeastsSporobolomyces roseus andCryptococcus laurentii var.flavescens were sprayed as a mixture (11) onto the fourth leaves of maize plants (Zea mays) two-three days prior to inoculation withColletotrichum graminicola. In four experiments the average yeast population of the treated leaves at the time of pathogen inoculation varied between 5× 10⁴ and 8× 10⁵ cells cm^–2 leaf, whereas on the untreated leaves the yeast population varied from <10³ to 10⁴ cells cm^–2 leaf. The yeasts reduced lesion density and necrosis fromC. graminicola infection by approximately 50%. Contrary to findings with other necrotrophic pathogens, conidial germination, superficial mycelial growth and appressorium formation were not affected. Instead, the reduction of infection could only be explained by a reduced number of penetrations from the normally formed appressoria, a site of interaction not previously recorded.Samenvatting In klimaatkastexperimenten werden maisbladeren (4e blad) twee-drie dagen voor inoculatie metColletotrichum graminicola bespoten met een mengsel (11) van de algemeen voorkomende fyllosfeergistenSporobolomyces roseus enCryptococcus laurentii var.flavescens. In vier experimenten varieerde de gemiddelde gistpopulatie op de behandelde bladeren, op het moment van inoculatie met het pathogen, van 5× 10⁴ tot 8× 10⁵ cellen cm^–2 blad, op de onbehandelde bladeren van <10³ tot 10⁴ cellen cm^–2 blad. De gisten reduceerden de lesiedichtheid en het necrotisch bladoppervlak tengevolge van deC. graminicola infectie voor ongeveer 50%. De stadia in de ontwikkeling van andere necrotrofe pathogenen, die gewoonlijk gevoelig zijn voor antagonisme door gisten, zoals sporekieming, oppervlakkige myceliumgroei en vorming van appressoria, werden bijC. graminicola niet beïnvloed. De waargenomen reductie van infectie kon alleen verklaard worden door een remming van de penetratie vanuit normaal gevormde appressoria. Interactie in dit stadium van het infectieproces is nog niet eerder waargenomen.     

Interactions between Plasmopara helianthi, Glomus mosseae and Two Plant Activators in Sunflower Plants

Interactions between Plasmopara helianthi, Glomus mosseae and two plant activators DL--amino-n-butyric acid (BABA) and CGA 245704 (acibenzolar-S-methyl (BTH)) in sunflower plants susceptible to downy mildew were studied in four experiments using different methods of treatment and pathogen inoculation. Both chemicals were applied as soil drenches and foliar sprays, whereas P. helianthi infection was obtained by root and cotyledon inoculations of the seedlings. Soil drenches at the rates of 50 and 100mgkg^–1 soil of BABA and BTH given 1 and 3 days before P. helianthi inoculation, respectively to mycorrhizal plants, provided moderate protection against the pathogen (about 50–55%). Morphological changes and decrease in mycorrhizal colonization in roots of BTH-treated plants and in BTH-treated mycorrhizal plants were also observed. Delay in the emergence and reduction of the root systems were more evident at the highest concentration but decreased with time. These effects were absent with the BABA treatment.Foliar spray treatment of BABA and BTH, applied at 4000 and 200µgml^–1, respectively (1 day post-inoculation) to mycorrhizal plants provided good protection (about 80%) against P. helianthi foliar infections. No effects on mycorrhizal colonization or on root systems were observed. In vitro tests on the effect of the compounds on the mycorrhizal fungus showed that the germination of G. mosseae sporocarps increased with BABA treatment whereas it was greatly inhibited by BTH treatment.     

Biological control of cucumber powdery mildew by Tilletiopsis minor

Samenvatting Onder optimale omstandigheden konT. minor de ontwikkeling van komkommermeeldauw (Sphaerotheca fuliginea) tegengaan.Spuiten met 2×10⁷ sporen ml^–17 dagen na inoculatie met komkommermeeldauw gaf een reductie van meeldauwontwikkeling van ongeveer 90%. Wanneer een tweede bespuiting met dezelfde concentratie sporen 3 dagen na de eerste werd toegepast bleven de planten vrij van meeldauw tot ze werden opgeruimd 3 weken later.Bij een R.L. lager dan 70% en een temperatuur boven 30 °C had geen van de behandelingen succes. T. minor bleek ongevoelig voor dimethirimol (Milcurb) bij een concentratie van 125 g ml^–1, terwijl er gemakkelijk een mutant kon worden verkregen, die resistent was tegen 100 g fenarimol ml^–1, bij gelijk blijvende groeikracht en pathogeniteit ten opzichte van komkommermeeldauw, waardoorT. minor ingepast kan worden in een schema voor geïntegreerde bestrijding.     

Induction of defence-related enzymes and resistance by the plant activator acibenzolar-S-methyl in tomato seedlings against bacterial canker caused by Clavibacter michiganensis ssp. michiganensis

Using tomato seedlings, the plant defence activator acibenzolar-S-methyl (benzo-[1,2,3]-thiadiazole-7-carbothioic acid-S-methyl ester, ASM; Bion 50 WG) was assayed for its ability to induce resistance against Clavibacter michiganensis ssp. michiganensis , the causal agent of bacterial canker of tomato. In ASM-pretreated plants, reduction in disease severity (up to 76·3%) was correlated with lower bacterial growth (up to 68·2% lower) during the time course of infection. To understand the possible mechanism of action of ASM, alterations in the activities of peroxidase (POX) and chitinase were assessed as markers of resistance. The enhanced resistance of ASM-treated plants was associated with significant increases in the activities of POX and chitinase     

Effect of acetochlor treatment on Fusarium wilt and sugar content in melon seedlings

Pretreatment of soil with the herbicide acetochlor at 0.1–1g g^–1 significantly decreased incidence of wilt due toFusarium oxysporum f. sp.melonis in melon seedlings. Glucose, fructose and sucrose increased in leaves of inoculated and uninoculated melon plants following acetochlor treatment. The increase in sugar levels in stems and roots was less pronounced. Light intensity affected sugar content and disease incidence. The percentage of diseased plants was significantly higher in untreated plants grown under 165E m^–2 sec^–1 compared to plants grown under 300E m^–2 sec^–1. Lowering light intensity resulted in reduction of levels of total sugars on the third and sixth day after inoculation. Acetochlor had little or no effect on growth rate or sporulation of the pathogen in culture. The colonization rate of diseased plant stems by the pathogen was similar in herbicide-treated and untreated plants, thus excluding the possibility that disease reduction by the herbicide is related to direct fungitoxicity.Contribution from the Agricultural Research Organization. No. 1560-E, 1995 series.     

Effect of benomyl on soil fungi associated with rye. 1. Effect on the incidence of sharp eyespot caused by Rhizoctonia cerealis

Effects of benomyl on incidence of pathogens affecting the culm base of rye were studied in field trials and growth chamber experiments. Spraying of the crop with the fungicide at a high dosage (2.4 kg.ha^–1) resulted in a tenfold increase of sharp eyespot caused byRhizoctonia cerealis and reduced foot rot symptoms caused by fusaria by 50%. In a field trial at a low dosage (0.24 kg.ha^–1) a slight increase of sharp eyespot was observed. In one year, probably because of wet conditions during the infection period, sharp eyespot did not occur in either benomyl-treated or untreated plots, but eyespot caused byPseudocercosporella herpotrichoides was abundant. Its occurrence was reduced from 74% affected culm bases in untreated plots to 8% and 1% in plots that received 0.24 and 2.4 kg.ha^–1 of the fungicide, respectively.In growth chambers seedlings were grown in two sandy soils inoculated withR. cerealis. The soil was kept dry at about 35% of the moisture holding capacity. In plots with benomyl (1 mg.kg^–1; moisture content 11% of fresh weight), fewer seedlings emerged than in plots without the fungicide. This result was highly significant (P<0.01) for one soil but not for the other. The number of seedlings that remained free of disease symptoms was higher (P<0.01) in untreated than in fungicide-treated plots of both soils.Isolates of pathogens obtained from diseased culms were tested for their sensitivity to benomyl. Growth of all of them includingR. cerealis was inhibited, although not always completely suppressed, at 10 g.ml^–1 on potato-dextrose agar. ED₅₀ values of most isolates ofR. cerealis were between 2.2 and 3.1 g.ml^–1. The fungus was slightly but consistently less sensitive thanF. culmorum. Mycelial growth ofF. nivale was appreciably more sensitive than that of the otherFusarium spp. from cereals.P. herpotrichoides andF. nivale were the most sensitive pathogens tested with ED₅₀ values of <1 g.ml^–1. Accordingly,F. nivale was absent on culms from treated plots. In a growth chamber experiment, seedlings were protected from infection by supplying the fungicide (1 mg.kg^–1) to previously inoculated soil.In a laboratory assay the effect of benomyl on microbial antagonism toR. cerealis was estimated for rhizosphere soil. Enhanced incidence of sharp eyespot in treated crops was associated with adverese effects of the fungicide on microbial antagonism. There is presumptive evidence thatR. cerealis is suppressed by bacteria after wet periods during the vegetation period of the crop and by fungi after dry periods. Only fungal antagonism, which may be less effective, is affected by benomyl. The response to benomyl of the microflora in different soils varied. Reasons for this inconsistency are suggested.Samenvatting In veldproeven en in een klimaatkamer werd de invloed van benomyl op het optreden van voetziekten in rogge onderzocht. In veldjes die bespoten waren met een hoge dosis van het fungicide (in totaal 2.4 kg.ha^–1) bleken tienmaal zoveel halmen met scherpe oogvlekken, veroorzaakt doorRhizoctonia cerealis, voor te komen dan in onbespoten veldjes. Daarentegen was voetrot veroorzaakt doorFusarium-soorten met 50% verminderd. In een volgende veldproef, waarbij een voor de praktijk geadviseerde dosis (0.24 kg.ha^–1) was toegepast, werd een lichte toename van scherpe oogvlekken waargenomen.In een ander jaar trad scherpe oogvlekkenziekte in het geheel niet op, ook niet in met benomyl behandelde veldjes. De vochtige omstandigheden tijdens de infectieperiode zijn daarvan waarschijnlijk de oorzaak. Daarentegen werd de oogvlekkenziekte, welke doorPseudocercosporella herpotrichoides werd veroorzaakt, veel aangetroffen. In de onbehandelde veldjes waren 74% van de halmen aangetast tegen 8 en 1% in de veldjes die met het fungicide waren behandeld in doseringen van 0.24 en 2.4 kg.ha^–1.De invloed van het fungicide op de aantasting van kiemplanten werd in klimaatkamerproeven onderzocht. Daartoe werden twee zandgronden metR. cerealis geënt. De grond werd droog gehouden (op 35% van het waterhoudend vermogen). In grond met fungicide (1 mg.kg^–1) was de opkomst minder dan in grond zonder fungicide. Dit was zeer significant (P<0.01) voor één van de beide zandgronden, maar niet voor de andere. Het aantal gezonde kiemplanten was in beide gevallen duidelijk hoger (P<0.01) voor de onbehandelde grond.De isolaten van ziekteverwekkers uit aangetaste halmen werden op hun gevoeligheid voor het fungicide getoetst. Op aardappel-glucoseagar werden alle isolaten in hun groei geremd bij een benomyl-concentratie van 10 g.ml^–1.R. cerealis was iets minder gevoelig danF. culmorum. Voor het overgrote deel van de isolaten vanR. cerealis lag de ED₅₀ waarde tussen 2,2 en 3,1 g.ml^–1. De myceliumgroei vanF. nivale werd meer geremd dan die van de andereFusarium-soorten.P. herpotrichoides enF. nivale waren met een ED₅₀ waarde van <1 g.m.^–1 de gevoeligste pathogenen die uit de halmvoeten werden geïsoleerd. Dat de populatie vanF. nivale in benomylhoudende grond wordt onderdrukt, blijkt uit (1) het feit dat de schimmel niet voorkwam op halmen uit behandelde veldjes en (2) de bescherming tegen infectie van kiemplanten als aan de besmette grond fungicide (1 mg.kg^–1) was toegevoegd.In laboratoriumproeven werd de invloed van benomyl op het microbiële antagonisme in rhizosfeergrond tegenR. cerealis bepaald. Een toename in het optreden van scherpe oogvlekkenziekte in behandelde gewassen bleek gepaard te gaan met een remming van het antagonisme tegen de ziekteverwekker. Er zijn sterke aanwijzingen datR. cerealis na vochtige perioden tijdens de vegetatieperiode door bacteriën wordt onderdrukt en na droge perioden door schimmels. Het antagonisme van de laatste groep lijkt minder effectief te zijn en alleen dit antagonisme wordt door benomyl verlaagd. Tenslotte wordt een mogelijke oorzaak aangegeven voor de ongelijke respons op het fungicide van het microbieel antagonisme in verschillende gronden.     

工业废水对黄瓜幼苗生长及叶片抗氧化系统的影响

采用以甘肃省境内某地区化肥厂、造纸厂的工业废水以及此两厂的混合废水作溶剂的培养液(分别记作废液1、废液2和废液3)培养黄瓜幼苗,研究了其对黄瓜幼苗的生长及其叶组织中活性氧清除系统的影响。结果发现,(1)培养5 d后,生长在废液1中的幼苗,叶片组织中的几种抗氧化酶除APX的活性显著增加外(P<0.01),CAT、SOD和GR活性均无明显变化(P>0.05)。生长在废液2中的CAT和GR的活性基本未变,APX和SOD的活性分别在P<0.01和P<0.05的水平上增加。在废液3中,CAT和SOD及APX的活性分别在P<0.05和P<0.01的水平上增加,而GR活性降低(P<0.05)。(2)培养13 d后,无论在哪种废水中,黄瓜幼苗的伸长生长和干物质积累及叶片组织中APX、SOD、CAT和GR活性、GSH和ASA含量均明显降低(P<0.05或P<0.01),H2O2、O2、MDA含量和电解质泄漏率明显增加(P<0.05或P<0.01)。结果表明,化肥厂、造纸厂的工业废水以及此两厂的混合废水对黄瓜幼苗叶组织中的抗氧化系统有明显的破环作用,最终影响幼苗的生长。     

Relation of Japanese <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> pv. <Emphasis Type="Italic">vesicatoria</Emphasis> with worldwide strains revealed with three specific monoclonal antibodies

Strains of Xanthomonas campestris pv. vesicatoria Dye 1978 (Xcv), the causal agent of bacterial spot, have been classified into two groups based on their ability to hydrolyze starch. Three monoclonal antibodies (MAbs), 7AH10, 5HB3, and 4AD2, were produced immunized against the living bacteria and were specific to and could distinguish Xcv strains able or unable to hydrolyze starch (Amy⁺ or Amy^–). The MAb 7AH10, obtained against strain UPB141(Amy^–) reacted in an enzyme-linked immunosorbent assay with all the Amy^– strains (n = 19) and 1 of 11 Amy⁺ strains. Against Xcv 2625, an Amy^– unusual phenotype strain, MAb 5HB3, recognized 97% of our worldwide collection of Xcvs (n = 30). Also against that strain, the MAb 4AD2 reacted with none of the homologous Amy^– phenotypes and with 90% (n = 11) of the heterologous Amy⁺ phenotypes. For all the MAbs, cross reactions with other pathovars or species were less than 4% (n = 67). By assaying a Japanese collection of strains against the three MAbs, the Amy⁺ strains were distinguished from the Amy^– strains, and their relation with other world strains could be demonstrated. All the MAbs reacted with the lipopolysaccharide fraction of the bacterial cell wall during immunoblotting.     

苦豆子内生真菌诱导子促进宿主生物碱合成积累的生理防卫反应

分别以4株苦豆子内生真菌菌液浓缩物为诱导子，研究不同诱导时间下，各诱导子对苦豆子组培苗中氧化苦参碱（OMA）含量以及防御酶苯丙氨酸解氨酶（PAL）、过氧化物酶（POD）、抗坏血酸过氧化物酶（APX）和过氧化氢酶（CAT）活性的影响。结果显示：4种苦豆子内生真菌的菌液浓缩物均可提高宿主中OMA的积累，其中诱导效果最佳的是内生真菌诱导子XKYKDF₄₀，在0~15 d诱导期间宿主中OMA含量持续增长且始终高于对照，在诱导第15 d达到最高，为3.616 mg·g^-1，是同时期对照组的2.09倍。4种内生真菌诱导子还可诱发宿主中生物碱合成关键酶PAL和3种抗氧化酶（POD、APX和CAT）活性升高。诱导子XKYKDF₄₀激发PAL活性的作用最佳，在诱导第6 d PAL活性达最大值，为61.92 U·g^-1，是同时期对照组的1.42倍；与其他诱导子相比，诱导子XKZKDF₂₇能够明显诱发POD的活性，在诱导第12 d达到最大值，为62.30 U·mg^-1，是同时期对照组的2.70倍；诱导子XKZKDF₁₁可诱导宿主中的APX和CAT活性大幅度提高，在诱导第12 d酶活性达到最高，分别为0.5538 U·mg^-1和19.82 U·mg^-1，是同时期对照组的4.97倍和3.00倍。结果表明，苦豆子内生真菌诱导子的加入不仅激活了宿主组培苗的防御性应答反应，还促进了OMA的合成。     

Exogenously applied hexaconazole ameliorates salinity stress by inducing an antioxidant defense system in Brassica napus L. plants

The ability of hexaconazole (HEX) to ameliorate salinity stress was studied in canola plants (Brassica napus L.). Canola seedlings were subjected to sodium chloride (NaCl) treatment. A treatment with 200 mM NaCl reduced growth parameters, chlorophyll content and protein content as well as increased the proline (Pro) content in canola plants. In addition, NaCl stress increased the endogenous, nonenzymatic antioxidants and the activity of antioxidant enzymes, such as peroxidase (POX; EC 1.11.1.7), superoxide dismutase (SOD; EC 1.15.1.1) and catalase (CAT; EC 1.11.1.6). When these plants were treated with a combination of NaCl and 50 mg L⁻¹ HEX, the inhibitory effects of NaCl stress were decreased by increasing the root growth, shoot growth, dry weight (DW), chlorophyll content, protein content and antioxidant enzyme activity by ameliorating the salinity injury. These results suggested that HEX has an important role in the enhancement of plant antioxidant systems and resistance to salinity in canola plants.     

Effect of Fungicides on Fusarium Head Blight and Deoxynivalenol Content in Durum Wheat Grain

In 1998–99 and 1999–2000 six trials were conducted to evaluate the effect of fungicides on Fusarium head blight in the field, on infected kernels and deoxynivalenol (DON) concentration in grain. A single application of prochloraz, tebuconazole, epoxiconazole or bromuconazole, applied to durum wheat varieties at the manufacturer's recommended dose at the beginning of anthesis stage, provided good control of the disease when infective pressure in the field was low to medium, and when the main pathogens were F. graminearum and F. culmorum. Kresoxim-methyl showed a low efficacy at controlling the disease. Tebuconazole, prochloraz and bromuconazole were effective at controlling F. graminearum and F. culmorum, while kresoxim-methyl was not effective in reducing Fusarium infected kernels. DON concentration in grain of cultivars inoculated with F. graminearum and F. culmorum was high, averaging 4.2mgkg^–1 (untreated control). Tebuconazole, prochloraz and bromuconazole reduced DON concentration by 43%, while epoxiconazole was ineffective. DON concentration in kernels of naturally infected cultivars was 1.95mgkg^–1, a concentration which exceeds the 1mgkg^–1 maximum level of contamination allowed in the United States. Furthermore prochloraz, bromuconazole and tebuconazole applications, in the naturally inoculated trials, reduced DON concentration from 73% to 96%, while epoxiconazole showed the lowest effectiveness. Moreover, a positive linear correlation between Fusarium infected grains and the DON concentration was observed.     

Epidemiology of Fusarium Infection and Deoxynivalenol Content in Winter Wheat in the Rhineland, Germany

Details of our long-term research programme concerning the epidemiology of Fusarium spp. and mycotoxin production are summarized. Evaluation of the occurrence of Fusarium spp., mainly on winter wheat (Triticum aestivum), was carried out by investigating Fusarium infection and mycotoxin contamination. Two to 15% of grains were infested during 1995–1998 at three climatologically differing localities of the Rhineland, Germany. Disease progress was accelerated by rainfall during the flowering season. The species most frequently isolated were Fusarium avenaceum, F. poae, F. culmorum and F. graminearum. The mean deoxynivalenol (DON) content varied from 19gkg^–1 (1995) to 310gkg^–1 (1998) and was not always correlated with disease severity. Organic farming systems showed lower rates of infection with ear blight and lower mycotoxin contamination than conventional farming systems.     

Correlation between field disease and latent infection by Glomerella cingulata of strawberry plants as revealed by a simple diagnostic method using ethanol immersion

Leaves of strawberry plants growing in fields were collected and assayed by ethanol immersion treatment (SDEI) to detect latent infection by Glomerella cingulata and Dendrophoma obscurans. SDEI revealed that 83% of the plants in growers fields were latently infected by G. cingulata and 58% by D. obscurans. In such fields, only 0.8%–2.5% of the plants later became wilted or died because of G. cingulata. When the latently infected plants from naturally infested fields were kept under optimal conditions for disease development for 5 weeks, 70.0%–83.3% of them wilted or died from G. cingulata. However, only 5.6%–6.7% of the plants diagnosed by SDEI as being without latent infection wilted or died. The results indicate the importance of selecting healthy plants, suggesting that SDEI is an effective method for detecting latent infection and reducing losses from G. cingulata.     

Comparison of Physical, Chemical and Biological Methods of Controlling Garlic White Rot

Treatment of garlic cloves with tebuconazole (at 1ml of Folicur 25% l^–1) achieved a significant reduction in the rate of disease progress and the final incidence of plant death by Sclerotium cepivorum: garlic yields were improved. Although soil solarization provided the best control of garlic white rot, bringing soil populations of S. cepivorum to negligible levels, similar levels of disease control and garlic yields were achieved when tebuconazole was sprayed to stem bases of plants grown from cloves also treated with tebuconazole. This double treatment almost doubled the yield compared with untreated plants and significantly increased bulb quality under high disease pressure conditions. Soil solarization was also highly effective in a second consecutive crop of garlic, with significant improvements in yield and garlic quality. In contrast, lower levels of disease control were obtained when selected isolates of Trichoderma harzianum and Bacillus subtilis were applied to the soil and cloves respectively.