Relative resistance of transgenic tomato tissues expressing high levels of tobacco anionic peroxidase to different insect species.

Different parts of genetically transformed tomato (Lycopersicon esculentum L.) plants that express the tobacco anionic peroxidase were compared for insect resistance with corresponding wild type plants. Leaf feeding by first instar Helicoverpa zea and Manduca sexta was often significantly reduced on intact transgenic plants and/or leaf disks compared to wild type plants, but the effect could depend on leaf age. Leaves of transgenic plants were generally as susceptible to feeding damage by third instar Helicoverpa zea (Boddie) and Manduca sexta (L.) as wild type plants. Green fruit was equally susceptible to third instar larvae of H. zea in both type plants, but fruit of transgenic plants were more resistant to first instar larvae as indicated by significantly greater mortality. Basal stem sections were more resistant to neonate larvae of H. zea and adults of Carpophilus lugubris Murray compared to wild type plants as indicated by significantly greater mortality and/or reduced feeding damage. Thus, tobacco anionic peroxidase activity can increase plant resistance to insects in tomato, a plant species closely related to the original source plant species, when expressed at sufficiently high levels. However, the degree of resistance is dependent on the size of insect and plant tissue involved.     

Overexpression of tomato <Emphasis Type="Italic">tAPX</Emphasis> gene in tobacco improves tolerance to high or low temperature stress

In order to investigate the function of chloroplast ascorbate peroxidase under temperature stress, the thylakoid-bound ascorbate peroxidase gene from tomato leaf (TtAPX) was introduced into tobacco. Transformants were selected for their ability to grow on medium containing kanamycin. RNA gel blot analysis confirmed that TtAPX in tomato was induced by chilling or heat stress. Over-expression of TtAPX in tobacco improved seed germination under temperature stress. Two transgenic tobacco lines showed higher ascorbate peroxidase activity, accumulated less hydrogen peroxide and malondialdehyde than wild type plants under stress condition. The photochemical efficiency of photosystem 2 in the transgenic lines was distinctly higher than that of wild type plants under chilling and heat stresses. Results indicated that the over-expression of TtAPX enhanced tolerance to temperature stress in transgenic tobacco plants.     

Expression of the <Emphasis Type="Italic">zga</Emphasis> agglutinin gene in tobacco can enhance its anti-pest ability for peach-potato aphid (<Emphasis Type="Italic">Myzus persica</Emphasis>)

The effect of introduction of the Zephyranthes grandiflora agglutinin gene (zga) to tobacco on its anti-pest ability for peach-potato aphids was investigated. PCR analysis confirmed that the zga gene was integrated into the plant genome. The results from semi-quantitative RT-PCR and real-time PCR assays revealed that the zga gene was expressed at various levels in the transgenic plants. A bioassay with aphids indicated that transgenic plants conferred enhanced resistance to aphids. Compared with the controls, the average number of aphids fed with transgenic plants during a 20-day assay evidently decreased by 70.4% in leaf disc bioassay and 77.9% in whole plant bioassay. The average number of nymph was significantly reduced by 36.4% on zga-expressing plants in leaf disc bioassay and 35.6% in whole plant bioassay. The report indicated that the introduction of zga gene to tobacco plants is a useful method to improve its anti-pest ability for aphids.     

Effect of transgenic plants expressing high levels of a tobacco anionic peroxidase on the toxicity of Anagrapha falcifera nucleopolyhedrovirus to Helicoverpa zea (Lepidoptera: Noctuidae)

Wild type and corresponding transgenic tomato (Lycopersicon esculentum Miller) and two tobacco (Nicotiana spp.) plants that express high levels of a tobacco anionic peroxidase were used to determine what type of interactions occurred between peroxidase altered plant chemistry and the baculovirus Anagrapha falcifera nucleopolyhedrovirus (AfMNPV) for control of neonate corn earworms, Helicoverpa zea (Boddie). Transgenic plants expressed approximately five to 400 times higher peroxidase activity than corresponding tissues of wild type plants. The H. zea larvae typically fed 1.5 times less on transgenic compared with wild type leaf disks. There was only one experiment (of three with tomato leaves) where the larvae that fed on transgenic leaves were less susceptible to the virus based on nonoverlapping 95% confidence intervals for LC50 values. When the exposure dose was corrected for reduced feeding on the transgenic leaf disks, the insecticidal activity of the virus was not significantly different for larvae fed on transgenic versus wild type plants. Eight other experiments (with tomato and two species of tobacco) indicated either no significant effect or enhanced susceptibility (when corrected for feeding rates) to the virus of larvae fed on the transgenic leaves. These results indicate enhanced insect resistance in plants expressing high levels of a specific anionic peroxidase may be compatible with applications of AfMNPV. Potential reasons for this compatibility are discussed.     

The jasmonate pathway alters herbivore feeding behaviour: consequences for plant defences

The jasmonate pathway is a highly conserved defensive cascade in plants that regulates the induction of resistance against herbivores; however, its role in herbivore feeding behaviour remains unknown. We used a mutant tomato plant (def‐1) deficient in the production of jasmonate‐related defensive proteins to test the hypothesis that genotypes with a reduced ability to induce resistance have a higher and more concentrated pattern of herbivore damage. Wild‐type and def‐1 plants received either damage by Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) caterpillars or no damage. After treatment, we tested for systemic responses by allowing a free roaming S. exigua caterpillar to feed on the undamaged portions of plants. Weight‐gain and leaf consumption of S. exigua were highest on def‐1 plants, regardless of prior herbivore damage. Def‐1 plants also had fewer numbers of leaves and leaflets eaten, and fewer feeding holes, which was indicative of a more concentrated distribution of damage on mutant compared to wild‐type plants. Following these results, we mimicked the amount and distribution of feeding damage that wild‐type or jasmonate‐deficient plants would receive on wild‐type plants to test whether changes in feeding behaviour may feedback to influence the expression of induced resistance. We mimicked the distribution of damage in wild‐type and jasmonate‐deficient plants by allowing caterpillars to feed on either one (leaf 1 or 2) or two leaves (leaf 1 and 2). Increased herbivore damage resulted in higher proteinase inhibitor (PI) activity, a jasmonate‐regulated defensive protein, and lower S. exigua performance on wild‐type but not jasmonate‐deficient plants. Compared to undamaged plants, a concentrated pattern of herbivore damage increased systemic resistance; these induced responses were greater on leaflets with stronger vascular connections to the damaged leaf. A more dispersed pattern of caterpillar damage altered the expression of induced responses, but the outcome depended on the specific pattern of damage. When leaf 1 was damaged and then leaf 2, the undamaged (third) leaf (which is more strongly connected to leaf 1 than 2) expressed reduced the PI activity compared to plants receiving concentrated damage to leaf 1; whereas in plants where leaf 2 was first damaged and then leaf 1, there were no differences in PI activity in leaf 3 compared to plants receiving concentrated damage to leaf 2. Thus, induction of the jasmonate pathway may not only determine the amount and distribution of feeding damage by herbivores, but this may feedback to affect the subsequent expression of plant defence.     

Effects of Aphis fabae and Uromyces viciae-favae on the growth of a susceptible and an aphid resistant cultivar of Vicia faba

Damaging effects of either black bean aphid (Aphis fabae), broad bean rust (Uromyces viciae-fabae), or the combination of both were investigated on a susceptible (cv. Diana) and an aphid resistant (cv. Bolero) cultivar of Vicia faba. When compared with rust, aphids caused greater reductions of root dry weight, shoot dry weight, leaf area, and mean relative growth rate. The mean unit leaf rate was also reduced whereas the leaf area ratio was not affected. The damage caused per aphid was highest on the susceptible cultivar. Rust induced damage did not differ between the cultivars. Concomitant infestation with both pests only resulted in additive damage. The population development of aphids was delayed on partially resistant plants. High temperature and rust infection reduced the total number of aphids the plants were able to support but not the level of resistance. Thus the specific damaging effect per aphid was increased.     

Agrotis segetum granulosis virus as a control agent against field populations ofAgrotis ipsilon andA. Segetum [Lep.: Noctuidae] on tobacco,okra, potato and sugar beet in northern pakistan

Agrotis segetum Schiff granulosis virus (AsGV) propagated in Denmark was supplied against naturally occurring cutworm populations (A. ipsilon and to a less extentA. segetum) in experimental field plots of tobacco, okra, potato and sugar beet in northern Pakistan. AsGV doses varied between 4 × 10⁷ and 4 × 10¹¹ capsules per m² plot, and no. of applications between 1 and 3. One treatment with AsGV did not reduce cutworm damage significantly to tobacco seedlings and potato plants. Two treatments with AsGV reduced cutworm damage significantly. In tobacco, reduction was 64–82%, in okra and potato 85% and 77% respectively. Damage in sugar beet was reduced 78%. Three treatments with AsGV dis not reduce damage significantly better than two treatments. AsGV and the chemical insecticides Tamaran and Dieldrin, andBacillus thuringiensis (Thuricide) were about equally effective, reducing damage by 85%, 79%, 87% and 69%, respectively. No difference was found between the efficiency of highly purified AsGV to which activated charcoal was added and partially purified AsGV without charcoal.      

Alleviation of ultraviolet-C-induced oxidative damage through overexpression of cytosolic ascorbate peroxidase

Experiments were conducted to investigate the relationship between ultraviolet (UV) C-induced oxidative damage and the activity of ascorbate peroxidase (APX), using transgenic tobacco (Nicotiana tabacum L. cv. Petit Havana) plants overexpressing cytosolic APX gene (apx1). Transgenic plants having 2.3 fold higher total APX activity, as compared to the wild type plants, showed normal morphological characters. Exposure of 70-day-old plants to fixed intensity UV-C radiation caused an increase in the malondialdehyde (MDA) content in wild type as well as transgenic plants. However, the wild type plants showed significantly higher (p < 0.05) lipid peroxidation as compared to the transgenic plants. Higher proline accumulation was recorded in transgenic plants as compared to the wild type plants, after 24 hours of UV-C exposure. Although the ascorbate content decreased continuously with increasing exposure to UV-C radiation, yet the wild type plants exhibited higher ascorbate levels than the transgenic plants. A marked difference in H₂O₂ content, between the wild type and transgenic plants, was consistently observed up to 20 hours of UV-C exposure. A direct correlation of ascorbate, MDA and H₂O₂ levels was recorded with the extent of oxidative stress, signifying that these could be used as potential bio-marker molecules for oxidative stress. The results clearly demonstrate that overexpression of cytosolic APX can protect tobacco plants from UV-C-induced oxidative damage.     

AM真菌对紫花苜蓿茎点霉叶斑病及豌豆蚜为害的影响

苜蓿茎点霉(Phoma medicaginis)叶斑病和豌豆蚜(Acyrthosiphon pisum)是紫花苜蓿(Medicago sativa)生产中重要的病虫害,在自然条件下常混合发生。本研究以紫花苜蓿为植物材料,探究接种AM真菌后,紫花苜蓿被苜蓿茎点霉侵染时,植物自身的防御机制,以及对后续豌豆蚜为害的影响,以期明确AM真菌对其调控机制。结果表明:AM真菌可显著降低植株茎点霉叶斑病病情指数(P<0.05); AM真菌促进了紫花苜蓿生长(P<0.05),改变了植株抗氧化酶(超氧化物歧化酶(SOD)和过氧化氢酶(CAT))活性以及植物激素信号物质(水杨酸(SA))含量(P<0.05);病原菌侵染会诱导植物抗氧化防御系统活性增强,包括过氧化物酶(POD)、SOD、CAT和多酚氧化酶(PPO)(P<0.05),从而增加植物对后续虫害的抗性; AM真菌在植物受到病原菌胁迫时会发挥积极作用,显著提高植株的SOD和CAT活性(P<0.05),有效抑制病原菌侵染对植株造成的危害;而蚜虫为害则进一步加重了植物受到的损害,抑制了AM真菌对植物抗病性的正向调控。研究结果对...     

Expression of the peroxidase gene promoter (Shpx6b) from Stylosanthes humilis in transgenic plants during insect attack

Inducible promoters are important in regulating the expression of resistance genes when plants are attacked by insects or pathogens. Evaluation of the Shpx6b peroxidase promoter from the tropical forage legume Stylosanthes humilis[ Curtis MD, Rae AL, Rusu AG, Harrison SJ & Manners JM (1997) A peroxidase gene promoter induced by phytopathogens and methyl jasmonates in transgenic plants. Molecular Plant Microbial Interactions 10: 326–338] in transgenic tobacco plants Nicotiana tabacum L. (Solanaceae) demonstrated that this promoter could drive expression of both the β‐glucuronidase (GUS uidA gene of E. coli) and green fluorescent protein (GFP) reporter genes in leaf tissues during attack by chewing insects – larvae of potato tuber moth (PTM) Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae) and sucking insects – green peach aphids Myzus persicae Sulzer (Homoptera: Aphididae). Strong GUS expression was present in tissues next to cells damaged by PTM larvae 24 h after infestation. With aphid infestation, GUS expression was limited to sites of feeding, and was observed 48 h after infestation. The expression of GFP mirrored that of GUS expression for both treatments, but was normally detected 48 h after infestation. Similarly, the exogenous application of methyl jasmonate (MeJa) induced GUS uniformly across leaf tissue, and mechanical wounding activated GUS expression at wound sites, similar to PTM larvae. GFP expression was observed 48 h after treatment, and for mechanical wounding GFP was localised in a manner similar to PTM damage. For MeJa treatment, GFP expression was more pronounced in cells around the midrib, and it was not uniformly induced across the leaf tissue. GUS reporter gene levels were also assayed to quantify expression, and the results were consistent with the observed histological patterns of expression. The results presented here show that the Shpx6b promoter switches on the expression of linked genes after damage by insect herbivores, and could be useful in regulating the expression of heterologous genes for insect and/or pathogen resistance in transgenic plants.     

Over-expression of gsh1 in the cytosol affects the photosynthetic apparatus and improves the performance of transgenic poplars on heavy metal-contaminated soil

Recent studies of transgenic poplars over‐expressing the genes gsh1 and gsh2 encoding γ‐glutamylcysteine synthetase (γ‐ECS) and glutathione synthetase, respectively, provided detailed information on regulation of GSH synthesis, enzymes activities and mRNA expression. In this experiment, we studied quantitative parameters of leaves, assimilating tissues, cells and chloroplasts, mesophyll resistance for CO₂ diffusion, chlorophyll and carbohydrate content in wild‐type poplar and transgenic plants over‐expressing gsh1 in the cytosol after 3 years of growth in relatively clean (control) or heavy metal‐contaminated soil in the field. Over‐expression of gsh1 in the cytosol led to a twofold increase of intrafoliar GSH concentration and influenced the photosynthetic apparatus at different levels of organisation, i.e., leaves, photosynthetic cells and chloroplasts. At the control site, transgenic poplars had a twofold smaller total leaf area per plant and a 1.6‐fold leaf area per leaf compared to wild‐type controls. Annual aboveground biomass gain was reduced by 50% in the transgenic plants. The reduction of leaf area of the transformants was accompanied by a significant decline in total cell number per leaf, indicating suppression of cell division. Over‐expression of γ‐ECS in the cytosol also caused changes in mesophyll structure, i.e., a 20% decrease in cell and chloroplast number per leaf area, but also an enhanced volume share of chloroplasts and intercellular airspaces in the leaves. Transgenic and wild poplars did not exhibit differences in chlorophyll and carotenoid content of leaves, but transformants had 1.3‐fold fewer soluble carbohydrates. Cultivation on contaminated soil caused a reduction of palisade cell volume and chloroplast number, both per cell and leaf area, in wild‐type plants but not in transformants. Biomass accumulation of wild‐type poplars decreased in contaminated soil by more than 30‐fold, whereas transformants showed a twofold decrease compared to the control site. Thus, poplars over‐expressing γ‐ECS in the cytosol were more tolerant to heavy metal stress under field conditions than wild‐type plants according to the parameters analysed. Correlation analysis revealed strong dependence of cell number per leaf area unit, chloroplast parameters and mesophyll resistance with the GSH level in poplar leaves.     

Enhanced sensitivity to oxidative stress in transgenic tobacco plants with decreased glutathione reductase activity leads to a decrease in ascorbate pool and ascorbate redox state

To investigate the possible mechanisms of glutathione reductase (GR) in protecting against oxidative stress, we obtained transgenic tobacco (Nicotiana tabacum) plants with 30–70% decreased GR activity by using a gene encoding tobacco chloroplastic GR for the RNAi construct. We investigated the responses of wild type and transgenic plants to oxidative stress induced by application of methyl viologen in vivo. Analyses of CO₂ assimilation, maximal efficiency of photosystem II photochemistry, leaf bleaching, and oxidative damage to lipids demonstrated that transgenic plants exhibited enhanced sensitivity to oxidative stress. Under oxidative stress, there was a greater decrease in reduced to oxidized glutathione ratio but a greater increase in reduced glutathione in transgenic plants than in wild type plants. In addition, transgenic plants showed a greater decrease in reduced ascorbate and reduced to oxidized ascorbate ratio than wild type plants. However, there were neither differences in the levels of NADP and NADPH and in the total foliar activities of monodehydroascorbate reductase and dehydroascorbate reductase between wild type and transgenic plant. MV treatment induced an increase in the activities of GR, ascorbate peroxidase, superoxide dismutase, and catalase. Furthermore, accumulation of H₂O₂ in chloroplasts was observed in transgenic plants but not in wild type plants. Our results suggest that capacity for regeneration of glutathione by GR plays an important role in protecting against oxidative stress by maintaining ascorbate pool and ascorbate redox state.     

Leaf biomechanical properties as mechanisms of resistance to black cutworm (Agrotis ipsilon) among Poa species

Biomechanical properties can be important parameters in resistance of plants to herbivorous insects. As plants age, however, there can be dramatic changes in physical defenses that can then influence their susceptibility to insect herbivores. We measured changes in leaf biomechanical properties during ontogeny of Poa species and the relationship of these changes to the development of a generalist herbivore, the black cutworm, Agrotis ipsilon Hufnagel (Lepidoptera: Noctuidae), was investigated. Larvae were reared on two representative age classes, i.e., young (<60 days after planting) and old (>1 year after planting), of foliage in laboratory assays. Foliage generally reaches a peak fracture force between 80 and 109 days after planting depending on grass type. Foliage from old plants was significantly tougher than that of young plants, and black cutworm larvae reared on foliage from young plants gained significantly (ca. four times) more weight than those fed on foliage from old Poa plants. In addition, fracture force has a negative relationship with black cutworm development. Plant fiber, particularly neutral detergent fiber accounted for 65 and 46% of the variation in fracture force and larval development, respectively. These results provide additional insight into how plant ontogeny influences physical defenses to an insect herbivore in a grass system. Likewise, this is seemingly the first study to suggest a mechanism for host plant resistance to black cutworm. Plant fiber may be a useful trait to explore in plant improvement programs in which black cutworm is a primary pest (e.g., managed turfgrass).     

Tests of associational defence provided by hairy plants for glabrous plants of Arabidopsis halleri subsp. gemmifera against insect herbivores

1. Trichome‐producing (hairy) and trichomeless (glabrous) plants of Arabidopsis halleri subsp. gemmifera were investigated to test whether plant resistance to herbivory depends on the plants' phenotypes and/or the phenotypes of neighbouring plants (associational effects). 2. A common garden experiment was conducted in which the relative frequency of hairy and glabrous plants was manipulated. Two species of leaf‐chewing insects (larvae of a white butterfly and a cabbage sawfly) were found less often on hairy plants than on glabrous plants. By contrast, the numbers of aphids and flea beetles did not differ significantly between hairy and glabrous plants. For none of these insects did abundance depend on the frequency of the two plant morphs. 3. A field survey was conducted in two natural populations of A. halleri. In the first population, a species of white butterfly was the dominant herbivore, and hairy plants incurred less leaf damage than glabrous plants across 2 years. By contrast, in the other population, where flea beetles were dominant, there were no consistent differences in leaf damage between the two types of plants. In neither of the two populations was any evidence found of associational effects. 4. This study did not provide any conclusive evidence of associational effects of anti‐herbivore resistance, but it was discovered that trichomes can confer resistance to certain herbivores. Given the results of previous work by the authors on associational effects against a flightless leaf beetle, such associational effects of the trichome dimorphism of A. halleri were herbivore‐specific.     

Improving freezing tolerance of transgenic tobacco expressing sucrose: sucrose 1-fructosyltransferase gene from Lactuca sativa

Sucrose: sucrose 1-fructosyltransferase (1-SST) cDNA from Lactuca sativa, coding the enzyme responsible for lower degree polymers fructan biosynthesis, was cloned by RT-PCR and RACE methods. The 1-SST cDNA under the control of CaMV 35S promoter was introduced into tobacco by Agrobacterium-mediated leaf disc transformation protocol. Fructan synthesis in vitro and carbohydrate analysis showed that sense transgenic tobacco plant displayed sucrose: sucrose 1-fructosyltransferse activity. After freezing stress, significant increases in electrolyte leakage and malondialdehyde were found in the wild type and anti-sense transgenic plants, while no apparent differences were observed in sense transgenic plants. Meanwhile, water soluble carbohydrate, fructan and fructose of sense transgenic plants remarkably increased, compared with those of wild type and anti-sense plants. No significant difference was detected in superoxide dismutase activity between transgenic and wild type plants. The above results demonstrated that the expression of 1-SST gene improved the freezing resistance of transgenic tobacco plants.     

Interactions of Russian wheat aphid, a hymenopterous parasitoid and resistant and susceptible slender wheatgrasses

Interactions among three trophic levels of resistant and susceptible slenderwheat grasses, Elymus trachycaulum (Link) Goule ex Shinners ex. H.F. Lewis, Russian wheat aphid, Diuraphis noxia (Mordvilko), and a hymenopterous parasitoid were studied in the laboratory and greenhouse. These relationships were compared with a commercial susceptible wheat Triticum aestivum L. variety. Aphids reared on the resistant entries showed significantly lower weights and numbers. Significant reduction of parasitoid mummy weight and adult size was positively correlated with the effects on the aphids. Resistant entries also induced a longer prereproductive period for both the aphids and parasitoids. Numbers of aphids and aphid damage were significantly modified by the addition of parasitoids. Parasitism was higher on plants that did not have leaf rolling. These findings may indicate that antibiosis resistance studied here is not the most desirable because it decreases natural enemy vitality.     

Overexpression of bacterial catalase in tomato leaf chloroplasts enhances photo-oxidative stress tolerance

The Escherichia coli gene katE, which is driven by the promoter of the Rubisco small subunit gene of tomato, rbcS3C, was introduced into a tomato (Lycopersicon esculentum Mill.) by Agrobacterium tumefaciens‐mediated transformation. Catalase activity in progeny from transgenic plants was approximately three‐fold higher than that in wild‐type plants. Leaf discs from transgenic plants remained green at 24 h after treatment with 1 µm paraquat under moderate light intensity, whereas leaf discs from wild‐type plants showed severe bleaching after the same treatment. Moreover, ion leakage from transgenic leaf discs was significantly less than that from wild‐type leaf discs at 24 h after treatment with 1 µm paraquat and 10 mm H₂O₂, respectively, under moderate light intensity. To evaluate the efficiency of the E. coli catalase to protect the whole transgenic plant from the oxidative stress, transgenic and wild‐type plants were sprayed with 100 µm paraquat and exposed to high light illumination (800 µmol m^?2 s^?1). After 24 h, the leaves of the transgenic plants were less damaged than the leaves of the wild‐type plants. The catalase activity and the photosynthesis activity (indicated by the F_v/F_m ratio) were less affected by paraquat treatment in leaves of transgenic plants, whereas the activities of the chloroplastic ascorbate peroxidase isoenzymes and the ascorbate content decreased in both lines. In addition, the transgenic plants showed increased tolerance to the oxidative damage (decrease of the CO₂ fixation and photosystem II activity and increase of the lipid peroxidation) caused by drought stress or chilling stress (4 °C) under high light intensity (1000 µmol m^?2 s^?1). These results indicate that the expression of the catalase in chloroplasts has a positive effect on the protection of the transgenic plants from the photo‐oxidative stress invoked by paraquat treatment, drought stress and chilling stress.     

3种寄主上桃蚜的选择性及形态分化

桃蚜是一种重要的农业害虫,寄主广泛,种下分化复杂。以采自黄土高原旱作区桃树、烟草、甘蓝上的桃蚜为研究对象,通过叶片选择法、传统比较形态测定法研究了3种寄主上桃蚜的选择性及形态分化。结果表明:在3种寄主同时存在的情况下,烟草上的桃蚜嗜食烟草,表现为63.5%的桃蚜选择烟草叶,13.8%选择甘蓝叶,8.2%选择桃叶,而甘蓝和桃树上的桃蚜对原寄主没有表现出明显的嗜好性;从形态指标来看,3种寄主上的桃蚜在体长、触角末节长度、后足腿节长度、触角与体长的比例方面存在显著差异(P0.05),说明这几个特征可以作为区分这3种寄主上桃蚜的依据。综合分析可以初步认为黄土高原旱作区烟草上的桃蚜可能形成了寄主专化型-烟草型。     

Below‐ground nematode herbivory of resistant soybean cultivars impairs the performances of an above‐ground caterpillar and its parasitoid

1. Interactions between below‐ and above‐ground organisms have attracted interest in recent years, but less is known about the effect of root‐feeding nematodes on above‐ground trophic interactions between herbivores and their natural enemies. 2. This study examined whether the presence of the soybean cyst root nematode Heterodera glycines influences the performance of the above‐ground leaf‐chewing tobacco cutworm Spodoptera litura on soybeans, Glycine max, and whether this in turn affects the success of its parasitoid, Meteorus pulchricornis. Using three soybean cultivars that varied in the level of constitutive resistance to the tobacco cutworm, the study determined whether feeding by the nematode altered the developmental and reproductive performances of the caterpillar and its parasitoid. 3. Root feeding by the nematode slowed tobacco cutworm larval development time and reduced adult body weight. Root feeding by the nematode also had a negative effect on the caterpillar's parasitoid, by prolonging development time, decreasing adult body size and reducing fecundity. These effects increased in a linear trend and varied in magnitude depending on levels of soybean constitutive resistance. 4. These findings demonstrate that root feeding by the nematode can prime soybean plants with negative impacts on their herbivore and its parasitoid, and that the impact may vary in magnitude depending on levels of soybean constitutive defence. The results emphasise the need to integrate soybean constitutive and root nematode‐induced defences for a better understanding of below‐ and above‐ground organism interactions, and to allow insights to be gained into the improvement of soybean integrated pest management programmes.     

Location of resistance factors in the leaves of potato and wild tuber-bearing Solanum species to the aphid Myzus persicae

Analysis of electrically recorded feeding behaviour of aphids was combined with colony‐development tests to search for sources of resistance to Myzus persicae (Sulzer) (Homoptera: Aphididae) in tuber‐bearing Solanum species (Solanaceae), aiming at a reduction of potato leaf roll virus (PLRV) transmission. Twenty genotypes, originating from 14 gene bank accessions, representing 13 wild tuber‐bearing Solanum spp., three Solanum tuberosum L. (potato) cultivars, and one S. tuberosum breeding line, were selected. Colony‐development tests were carried out in no‐choice experiments by placing adult aphids on plants of each genotype and counting numbers of nymphs and adults on young plants after 8 and 15 days, and on flowering plants after 14 and 30 days. Large differences were observed among genotypes: some developed small colonies and others developed large ones. Also, in a few genotypes, resistance in mature plants was different for leaves of different ages; young leaves were resistant to aphids whereas old senescent leaves were susceptible. The electrical penetration graph (DC‐EPG system) technique was used to study aphid feeding behaviour on each Solanum genotype for 6 h. Electrical penetration graph (EPG) results also showed large differences among the genotypes, indicating resistance at the leaf surface and at three different levels of plant tissue (epidermis, mesophyll, and phloem). Therefore, it was concluded that different mechanisms of resistance to M. persicae exist among the genotypes analysed. EPGs recorded from aphids on Solanum berthaultii Hawkes and Solanum tarijense Hawkes with and without glandular trichomes showed that strong surface resistance can bias EPG parameters associated with resistance located in deeper tissues. Experimental evidence is presented that the resistance to aphids in the genotypes with glandular trichomes strongly depends on these morphological structures.