Suppression of phenylalanine ammonia-lyase activity elicited in date palm by Fusarium oxysporum f. sp. albedinis hyphal wall elicitor

The inoculation of the seedling roots of the resistant (Bousthami Noir) and susceptible (Jihel) date palm (Phoenix dactylifera) cultivars by Fusarium oxysporum f. sp. albedinis induced an increase in phenylalanine ammonia-lyase (PAL) activity. The response of the PAL activity in the resistant cultivar was faster and higher than in the susceptible one. However, the elicitation of the seedlings with the hyphal wall elicitor (HWE) of the pathogen induced identical PAL activity in both cultivars. In the resistant cultivar, the the PAL activity elicited with the HWE was not influenced by the addition of the fungal culture filtrate (FCF) whereas it was suppressed in the susceptible cultivar. This FCF suppressor effect was dose-dependent, not influenced by sodium periodate, whereas it was strongly reduced by the heat (121 °C for 45 min) and pronase E. These results show that differential induction of the defence mechanisms in both cultivars was not related to differences in the induction of the PAL activity, but to the suppression of its elicitation in the susceptible cultivar.     

Elicitor-induced metabolic changes in cell cultures of chickpea (Cicer arietinum L.) cultivars resistant and susceptible to Ascochyta rabiei

Cell-suspension cultures of two chickpea (Cicer arietinum L.) cultivars, resistant (ILC 3279) and susceptible (ILC 1929) to the fungus Ascochyta rabiei (Pass.) Lab., showed differential accumulation of the phytoalexins medicarpin and maackiain, and transient induction of related enzyme activities after application of an A. rabiei-derived elicitor. The chalcone-synthase (CHS) activity (EC 2.3.1.74) which is involved in the first part of phytoalexin biosynthesis exhibited a maximum 8–12 h after elicitation in the cells of both cultivars. Concomitant with the fivefold-higher phytoalexin accumulation, CHS activity increased twofold in the cells of the resistant cultivar. The maximum of the elicitor-induced CHS-mRNA activity was determined 4 h after onset of induction in the cultures of both cultivars, although in cells of cultivar ILC 3279 this mRNA activity was induced at a level twofold higher than that in cells of the susceptible race ILC 1929. Investigations of CHS isoenzymes by two-dimensional gel electrophoresis of immunoprecipitated in-vitro-translated protein indicated the presence of five proteins. In the cells of both cultivars only two of the isoenzymes were induced after elicitor treatment. Analysis of the total in-vitro-translated proteins by two-dimensional gel electrophoresis showed that the constitutively expressed patterns of mRNA activities in the cell cultures of the two cultivars were identical. After elicitation, considerably more translatable mRNAs were induced in the cells of cultivar ILC 3279. The few induced proteins, and their respective mRNA activities, which could be detected in the cells of the susceptible cultivar, all existed in the cells of the resistant cultivar, too. One highly induced protein (M_r 18 kDa) found in the cells of cultivar ILC 3279 reached its maximum mRNA activity 6 h after elicitor application. The amount of this protein was hardly increased in the cells of the susceptible cultivar. This protein appears to be excreted from the cells into the growth medium.Abbreviations CHS chalcone synthase - IEF isoelectric focussing - ILC international legume chickpea - PR-protein pathogenesis-related protein - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis Financial support by Deutsche Forschungsgemeinschaft and Fonds der Chemischen Industrie is gratefully acknowledged. The authors thank Dr. K. Hahlbrock (Max-Planck-Institut für Züchtungsforschung, Köln, FRG) for provision of antisera and the International Centre for Agricultural Research in the Dry Areas (Aleppo, Syria) for plant material.     

Induction of pathogenesis-related proteins in sugarcane leaves and cell-cultures by a glycoprotein elicitor isolated from <Emphasis Type="Italic">Colletotrichum falcatum</Emphasis>

The induction of pathogenesis-related (PR) proteins in sugarcane (Saccharum officinarum L.) leaves and suspension-cultured cells in response to treatment with a glycoprotein elicitor isolated from Colletotrichum falcatum (the red rot pathogen) was investigated. Treatment of leaves and cells with the elicitor resulted in a much marked increase in the activities of chitinase and β-1,3-glucanase in red rot resistant (BO 91) than susceptible (CoC 671) sugarcane cultivar. SDS-PAGE analysis revealed that C. falcatum elicitor induced the accumulation of several proteins in suspension-cultured cells of resistant cultivar (BO 91); among them the 35 kDa protein was predominant. Whereas, a 27 kDa protein was induced predominantly in the cells of susceptible cultivar upon treatment with the elicitor. When sugarcane leaves were treated with C. falcatum elicitor, two proteins with apparent molecular masses of 25 and 27 kDa were induced both in the resistant and susceptible cultivars. However, the induction was stronger in the resistant than the susceptible cultivar. Immunoblot analysis for chitinase indicated that a protein with an apparent molecular mass of 37 kDa cross-reacting with barley chitinase antiserum was strongly induced in the suspension cultured cells of both the cultivars. The induction of 37 kDa chitinase was more in the cells of resistant cultivar than in the susceptible cultivar. Western blot analysis revealed that a 25 kDa thaumatin-like protein (TLP) cross-reacting with bean TLP antiserum was strongly induced in leaves and cultured cells of both resistant and susceptible cultivars due to elicitor treatment.     

Phenylalanine Ammonia-lyase Activity in Barley After Infection with Bipolaris sorokiniana or Treatment with its Purified Xylanase

Phenylalanine ammonia-lyase (PAL) activity was determined from leaves and roots of two barley (Hordeum vulgare L.) cultivars after infection with a necrotrophic pathogen, Bipolaris sorokiniana (Sacc.) Shoem., and treatment with its purified xylanase. PAL activity increased in leaves of both cultivars 16 h after fungal inoculation but two phases, with activity peaks at 24–32 h and 40 h, were recorded only for the more resistant cultivar, Agneta. Attempts to use a PAL inhibitor, χ-amin, ooxyacetic acid, to increase susceptibility to B. sorokiniana in barley leaves were unsuccessful. Treatments of leaves with purified xylanase resulted in more rapid (4–12 h after injection), although reduced, induction of PAL compared with fungal injection. The higher the concentration of xylanase applied the earlier the activity peaks were detected. Fungal inoculation only slightly increased PAL activity in barley roots while xylanase treatment had no effect. The basal level of PAL was however much higher in roots than in leaves. In wheat, Triticum aestivum L. resistant to B. sorokiniana, the time-course of PAL induction after fungal infection and xylanase treatment resembled that for cv. Agneta, while in oats, Avena sativa L. (non-host) PAL activity did not change after the treatments. The results suggest that the second phase of PAL induction, associated only with responses of barley cv. Agneta and wheat, is linked with their resistance to B. sorokiniana infection. The possible role of xylanase as an elicitor of PAL is discussed.     

Elicitation of peroxidase activity and lignin biosynthesis in pepper suspension cells by Phytophthora capsici

Cell suspension cultures of three varieties of Capsicum annuum L., each with a different degree of sensitivity to the fungus Phytophthora capsici, responded to elicitation by both lyophilized mycelium and fungus filtrate with a hypersensitive reaction. They showed the synthesis or accumulation of PR-proteins with peroxidase (EC 1.11.1.7) activity and the accumulation of lignin-like polymer (as measured by derivatization with thioglycolic acid). The cultivation medium was optimised for both plant and fungus growth in order to avoid any stress during their combination. The resistant pepper variety, Smith-5, showed a more intense response to the elicitor preparations than the sensitive varieties, Americano and Yolo Wonder. This was particularly evident when the cell suspensions were elicited with the filtrate. After elicitation, the cell walls thickened through the accumulation of lignin, as can be observed by staining microscope preparations with methylene blue. Elicitation also reduced the level of total peroxidase activity in the susceptible varieties, while such activity increased in resistant varieties, and was accompanied by de novo expression of acidic peroxidase isoenzymes in the extracellular and cell wall fractions. Of note was the PR protein of pI 5.7 showing peroxidase activity, which was induced by both elicitor types in the elicited cell suspensions of the resistant variety alone, making it a marker of resistance. The increases in the activity of these peroxidases in the resistant variety are in concordance with the accumulation of lignin observed 24 h after inoculation by both elicitors from the fungus. The possible role of these isoenzymes in lignin biosynthesis, used to reinforce the cell walls against fungal penetration of the cells, is discussed. These results are in accordance with those previously observed in plant stem sections.     

Sorghum root length density and the potential for avoiding striga parasitism

Striga hermonthica is a serious root parasite of sorghum in the semiarid tropics. Successful parasitism is dependent on interactions of Striga seeds and host roots. Several sorghum cultivars have been found which resist parasitism. The basis of resistance is not well known. One possible method for reducing the chances of parasitism is by restricted host root development. This research was conducted to evaluate this hypothesis in sorghum known to possess resistance to parasitism by Striga.Root length density of 21-day-old pot-grown resistant cultivars, Framida, N-13, IS-9830, Tetron and P-967083, were compared to that of the susceptible check, Dabar, using the line intercept method of measuring root length. There was no significant difference between resistant cultivars and the susceptible cultivar Dabar. The RLD of resistant P-967083 however was significantly less than Framida, another resistant cultivar.The RLD of Dabar was compared to that of Framida and P-967083 in USA and Niger field trials. Root length density was determined on soil cores taken at flowering with a Giddings Soil Sampler. Each core was divided into 10-cm fractions for estimating RLD by the line intercept method. In the USA Dabar had significantly greater RLD than the two resistant cultivars in the upper 10-cm portion of the soil profile, but only significantly greater than P-967083 in the 10–20-cm portion. Significant differences in RLD between susceptible and resistant cultivars were not found at depths between 20–60 cm. In field trials in Niger, RLD of Dabar was significantly greater than either resistant cultivar in the (0 to 30 cm) portion of the soil core. These results suggest that part of the Striga resistance of P-967083 and perhaps Framida may be a result of avoiding interactions between parasitic seeds and host roots.     

Elicitor induction of furanocoumarin biosynthetic pathway in cell cultures ofRuta graveolens

Treatment with an autoclaved culture homogenate of the yeastRhodotorula rubra induces rapid accumulation of acridone epoxides, furoquinolines and furanocoumarins in cell cultures ofRuta graveolens (L). The increased accumulation is preceeded by an induction of enzymes of the biosynthetic pathways. In the case of furanocoumarins induction was shown for phenylalanine ammonia-lyase (PAL), 4-coumarate: CoA ligase (4-CL) and S-adenosyl-l-methionine: xanthotoxol O-methyltransferase (XOMT). For PAL and 4-CL time courses of induced activity showed an early maximum, 8–12 h after treatment, whereas XOMT was found to reach its maximum later, about 36–42 h after treatment. The elicitor dose-response curve showed saturation at an elicitor concentration of 1%. At any time during the whole culturing period cells responded to elicitiation but the maximum enzyme activities induced were lower at the late stages. Experiments with different suspension culture strains, a shoot teratoma culture and hydroponically grown sterile photomixotrophic plants were performed to assess the influence of differentiation on constitutive activities of these enzymes and their inducibility by elicitation. Constitutive furanocoumarin accumulation was positively correlated with the level of differentiation. Although induction of PAL, 4-CL and XOMT activity always accompanied induced furanocoumarin accumulation no absolute correlation existed between induced enzyme activities and the induced product level or relative product increase.Abbreviations 4-CL 4-coumarate:CoA ligase - COMT S-adenosyl-l-methionine:caffeic acid 3-O-methyltransferase - PAL phenylalanine:ammonia-lyase - XOMT S-adenosyl-l-methionine:xanthotoxol O-methyltransferase     

甘蔗鞭黑粉菌侵染甘蔗的早期可视化观察

[目的]甘蔗鞭黑粉菌(Sporisorium scitamineum)引起的甘蔗黑穗病是我国甘蔗生产重要的病害.示踪甘蔗鞭黑粉菌侵染甘蔗的过程将有助于揭示其致病性和甘蔗抗黑穗病机制,为抗病品种的选育以及黑穗病的防治奠定基础.[方法]利用农杆菌介导的遗传转化技术对甘蔗鞭黑粉菌进行黄色荧光标记,对转化子进行配合及致病力检测...     

Race cultivar-specific differences in callose deposition in soybean roots following infection with Phytophthora megasperma f.sp. glycinea

Primary roots of soybean (Glycine max (L.), Merrill, cv. Harosoy 63) seedlings were inoculated with zoospores from either race 1 (incompatible, host resistant) or race 3 (compatible, host susceptible) of Phytophthora megasperma f.sp. glycinea and total callose was determined at various times after inoculation. From 4 h onward, total callose was significantly higher in roots showing the resistant rather than the susceptible response. Local callose deposition in relation to location of fungal hyphae was determined in microtome sections by its specific fluorescence with sirofluor and was quantified on paper prints with an image-analysis system. Callose deposition, which occurs adjacent to hyphae, was found soon after inoculation (2, 3 and 4 h post inoculation) only in roots displaying the resistant response, and was also higher at 5 and 6 h after inoculation in these resistant roots than in susceptible roots. Early callose deposition in the incompatible root-fungus reaction could be a factor in resistance of soybean against P. megasperma.Abbreviation pi post inoculation     

Aphelinus albipodus(Hymenoptera: Aphelinidae) andDiaeretiella rapae(Hymenoptera: Braconidae) Parasitism onDiuraphis noxia(Homoptera: Aphididae) Infesting Barley Plants Differing in Plant Resistance to Aphids

Russian wheat aphid,Diuraphis noxia(Mordvilko), as a pest of small grains, has prompted research into biological control and host plant resistance. In the presence of Russian wheat aphid, leaves of a susceptible barley (Morex) are curled and chlorotic and sustain large densities of this aphid, while leaves of a resistant barley (STARS-9301B) remain flat and green and sustain fewer aphids. Might parasitism of Russian wheat aphid byAphelinus albipodusHayat & Fatima andDiaeretiella rapaeMcIntosh be affected differently by these plant types? When presented the plants separately and based on parasitism rate relative to aphid density, the largerD. rapaewas more effective in parasitizing relatively high densities of aphids within curled leaves of Morex than relatively low densities of aphids on uncurled leaves of STARS-9301B. Parasitism byA. albipodusdid not significantly differ among the plants. When given a choice of plants, approximately equal rates of parasitism occurred on the two plant lines for both parasitoid species, and parasitism byD. rapaewas greater thanA. albipodus.These data indicate that using parasitoid size as an indicator of success in a physically restricted environment may be misleading, when considered in a plant environment responsive in several manners to aphids (chlorosis, curling, and ability to sustain Russian wheat aphid). We expect that use of resistant barley will result in decreased parasitoid abundance as aphid densities decrease. However, parasitism rates are expected to be approximately equal on resistant and susceptible barley. In this system, plant resistance and biocontrol are compatible management strategies.     

广东花生主要品种对黑腐病菌的抗性水平鉴定

【背景】寄生帚梗柱孢霉是花生黑腐病的病原菌,被我国列为重要的进境植物检疫性有害生物。该病菌2009年已入侵我国广东,造成花生植株基部腐烂而死亡,严重威胁花生生产安全。筛选与种植抗病品种是防控该病害的重要措施。【方法】收集广东推广种植的15个主要花生品种,通过人工接种方法,鉴定这些品种对花生黑腐病菌的抗性水平。【结果】15个供试花生品种中,湛红2号、湛油62等2个品种表现为抗病;湛油75、湛油82、粤油390、粤油410、仲恺花44、仲恺花99、汕油诱1号等7个品种表现为中抗;花育33号、汕油523、汕油辐1号、粤油18、湛油53等5个品种表现为感病;仲恺花332表现为高感。【结论与意义】目前广东生产上推广种植的花生品种多数对黑腐病菌表现为抗病或中抗水平,部分品种表现为感病或高感。该结果可为我省花生品种的推广与布局提供依据。     

l-Phenylalanine ammonia-lyase in suspension culture cells of spruce (Picea abies)

The activity of l-phenylalanine ammonia-lyase (PAL) (EC 4.3.1.5) was determined in seedlings, callus cells, cell suspension cultures and in young needles of spruce (Picea abies) (L.) (Karst). PAL activity increased up to 10 fold in response to transferring suspension cultured cells into new cultivation medium. PAL was also induced about 10 fold when callus cells were transferrd into liquid medium. The increase was transient and it required the presence of a carbohydrate.In cell suspension cultures, grown in the dark (white cells), but not in light-grown cultures (green cells), PAL activity was induced up to 30 fold by UV-light.With a cell wall preparation of Rhizosphaera kalkhoffii, a forest pathogenic fungus, used as elicitor, the activity of PAL could be induced more than 10 fold. The degree of induction depended on the elicitor concentration. Induction was prevented by cycloheximide but not by actinomycin D.     

Colonization of Fusarium Wilt‐Resistant and Susceptible Watermelon Roots by a Green‐Fluorescent‐Protein‐tagged Isolate of Fusarium oxysporum f.sp. niveum

Interactions between watermelon and a green fluorescent protein (GFP)‐tagged isolate of Fusarium oxysporum f.sp. niveum race 1 (Fon‐1) were studied to determine the differences in infection and colonization of watermelon roots in cultivars resistant to and susceptible to Fusarium wilt. The roots of watermelon seedlings were inoculated with a conidial suspension of the GFP‐tagged isolate, and confocal laser scanning microscopy was used to visualize colonization, infection and disease development. The initial infection stages were similar in both the resistant and susceptible cultivars, but the resistant cultivar responded differentially after the pathogen had penetrated the root. The pathogen penetrated and colonized resistant watermelon roots, but further fungal advance appeared to be halted, and the fungus did not enter the taproot, suggesting that resistance is initiated postpenetration. However, the tertiary and secondary lateral roots of resistant watermelon also were colonized, although not as extensively as susceptible roots, and the hyphae had penetrated into the central cylinder of lateral roots forming a dense hyphal mat, which was followed by a subsequent collapse of the lateral roots. The initial infection zone for both the wilt‐susceptible and wilt‐resistant watermelon roots appeared to be the epidermal cells within the root hair zone, which the fungus penetrated directly after forming appressoria. Areas where secondary roots emerged and wounded root tissue also were penetrated preferentially.     

Fungal elicitor-mediated responses in pine cell cultures

A tissue culture system has been developed to examine phenylpropanoid metabolism induced in pine tissues by an ectomycorrhizal symbiont. An elicitor preparation from the ectomycorrhizal fungus Thelephora terrestris Fr. induced enhanced phenolic metabolism in suspension cultured cells of Pinus banksiana Lamb., as indicated by tissue lignification and accumulation of specific methanol-extractable compounds in the cells. Induction of lignification was observed as early as 12 h after elicitation. The activity of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5), the entry-point enzyme into phenylpropanoid metabolism, also increased within the same time-frame in elicited cells. Significant increases in PAL activity were evident by 6 h after elicitation, and, by 12 h after elicitation, PAL activity in elicited cells was ten times greater than that in the corresponding controls. Lignification of the elicited tissue was also accompanied by an increase in the activity of other enzymes associated with lignin synthesis, including caffeic acid O-methyl transferase (EC 2.1.1.46), hydroxycinnamate:CoA ligase (EC 6.2.1.12), cinnamyl alcohol dehydrogenase (EC 1.1.1.-), coniferin glucosidase (EC 3.2.1.21) and peroxidase (EC 1.11.1.7). The increase in total peroxidase activity was associated with a change in the pattern of soluble peroxidase isoforms. The pine cell culture-ectomycorrhizal elicitor system provides a good model for molecular analysis of the process of lignification in an economically important softwood species.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - 4CL hydroxycinnamate:Coenzyme A ligase (EC 6.2.1.12) - CAD cinnamyl alcohol dehydrogenase (EC 1.1.1.-) - COMT S-adenosyl-l-methionine:caffeate O-methyl transferase (EC 2.1.1.46) - HPLC high-pressure liquid chromatography - PAL phenylalanine ammonia-lyase (EC 4.3.1.5) - TGA thioglycolic acid To whom correspondence should be addressedFinancial assistance for this work was provided by the Natural Sciences and Engineering Research Council of Canada.     

Effect of seaweed concentrate fromEcklonia maxima (Osbeck) Papenfuss onMeloidogyne incognita infestation on tomato

Seaweed concentrate (SWC), prepared fromEcklonia maxima, when applied as a soil drench to tomato seedlings, significantly increased plant growth and reduced infestation byMeloidogyne incognita. Foliar applied SWC had little effect on plant growth and increased nematode galling. Ashing SWC reduced the suppressive effect on nematode infestation. In anin vitro experiment, SWC lessened infestation of root-knot nematodes on excised roots of a susceptible cultivar of tomato. Application of the same concentrations of SWC to a nematode-resistant cultivar increased the number of egg masses.     

Intracellular location of NADP+-linked malic enzyme in C3 plants

Ultraviolet light induces anthocyanin biosynthesis in cell cultures of an Afghan cultivar of Daucus carota (Daucus carota L. ssp. sativus). Simultaneous treatment with a fungal elicitor from Pythium aphanidermatum results in an inhibition of the catalytic activity of chalcone synthase (CHS), which in turn correlates with an inhibition of anthocyanin biosynthesis. On immunoblots, one isoenzyme (40 kDa) of CHS disappears upon elicitor treatment. On an mRNA level, only the mRNA for the 40-kDa-CHS is active after treatment with ultraviolet light. After inhibition of anthocyanin biosynthesis by the elicitor the enzyme protein disappears and the CHS mRNA is strongly diminished. This inhibition depends on the concentration of the elicitor. In addition, elicitor treatment leads to an induction of the general phenylpropanoid pathway as well as to the accumulation of 4-hydroxybenzoic acid which is covalently bound to wall polysaccharides of the carrot cells. The possible function of phenylalanine ammonia-lyase in providing precursors for 4-hydroxybenzoic acid is discussed.Abbreviations CHI chalcone isomerase - CHS chalcone synthase - PAL phenylalanine ammonia-lyase - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis We are grateful to Professor K. Hahlbrock (Max-Planck-Institut für Züchtungsforschung, Köln, FRG) for providing us with antisera to CHS and PAL, respectively. This work was supported by a grant from the Deutsche Forschungsgemeinschaft and scholarships from the Friedrich-Ebert-Stiftung (J. G.), the Landesgraduierten-förderungsgesetz Baden-Württemberg (J.-P. S) and the Gerhard-Rösch-Stiftung (D. S.). We thank R. Hofmann for her excellent technical assistance.     

Relationship between Cell Wall Susceptibility to Cellulases and Pectinases of Fusarium oxysporum and Susceptibility of Date Palm Cultivars

Fusarium oxysporum f. sp. albedinis, the bayoud disease agent of date palm, grows on a mineral medium containing the cell walls of date palm roots as a sole carbohydrate source. The growth and development of pathogen under these conditions was related to the production of extracellular cell wall-degrading enzymes (CWDE): cellulases, polygalacturonases, polygalacturonate transeliminases, and pectinmethylesterases. The mycelial growth and the sporulation of pathogen were higher in the presence of cell walls of susceptible cultivars (BFG, JHL, BSK) than in the presence of those of resistant cultivars (IKL, SLY, BSTN). After 8 d of fungal culture, the activity of CWDE was equal whatever is the origin of the cell walls (resistant or susceptible cultivars). After 16 d of culture, the activity of these CWDE was higher when the parasite was cultivated on the cell walls of the susceptible cultivars than on those of the resistant cultivars. A positive correlation was observed between CWDE activities and the growth and the sporulation of F. oxysporum after 16 d of culture. These results clearly show a relation between the susceptibility/resistance of the cell walls of the roots of the date palm to the parasitic CWDE and the susceptibility/resistance of the cultivars.     

Partial Characterization of Cytosolic Superoxide Dismutase Activity in the Interaction of Meloidogyne incognita with Two Cultivars of Glycine max

The closely related soybean (Glycine max) cultivars Centennial and Pickett 71 were confirmed to be resistant and susceptible, respectively, to the root-knot nematode Meloidogryne incognita. Increases in superoxide dismutase (SOD) activity were detected in roots of both soybean cultivars 48 hours following inoculation. Superoxide dismutase activity increased in roots of the susceptible cultivar overall, but declined after 96 hours in roots of the resistant cultivar. The isoelectric points of SOD isolated from preparasitic and parasitic developmental stages of the nematode appeared to differ. The SOD activity increased dramatically as nematodes matured and enlarged. Plant and nematode SOD were present as ca. 40-kDa cuprozinc dimers. Initial increases in SOD activity in infected tissue appeared to involve nematode regulation of plant gene expression. However, as the nematode enlarged, SOD activity could be detected within the female body only.     

Relationship between root respiration and seedling age in tomato cultivars infested by Meloidogyne incognita

Measurements were made of respiration in the roots of tomato cultivars susceptible and resistant to Meloidogyne incognita. Nematode infestation of the susceptible cv. Roma VF caused an initial stimulation of the total respiration with an increase in the CN-sensitivity; the effect decreased and then disappeared as the seedlings aged. In the resistant cv. Rossol nematode infestation initially caused an inhibition of total respiration and a decrease in the CN-sensitivity; respiration and CN-sensitivity increased with seedling age. The activity of the alternative respiration pathway (m-chlorobenzhydroxamic acid-sensitive) was unchanged by nematode infestation in the resistant cultivar and increased markedly in the susceptible cultivar during the early stages of infestation.     

Antibiosis and antixenosis of chrysanthemum cultivars to the aphidAphis gossypii

An assessment was made of the antibiotic and antixenotic resistance of three cultivars of autumn flowering chrysanthemum (derived fromDendranthema morifolium (Ramat) Tzvelev andD. indicum (L.) Desmoulins) to the aphidAphis gossypii Glover. Antibiosis was also assessed at the top, middle and lower leaves of the plant. The three cultivars showed a range of resistance with Hero being the most susceptible, Surfine the most resistant and Purple Anne intermediate. There was a trend for antibiosis to improve with position down the plant, however there were cultivar by position interactions. Antixenosis was assessed at two levels, the first being under conditions where the aphid had complete access to the plant in caged choice assays and the second being under conditions where the aphid only had host odour to assess under olfactometer choice conditions. Preferences under the caged choice conditions found Hero to be the most preferred cultivar while there was no preference shown between Purple Anne and Surfine. However, olfactometer assessments showed Hero to be the least preferred of the three cultivars and, again, no preferences could be found between Purple Anne and Surfine.