Major Component Of Resistance Research Articles

Pan-cancer analysis of IDO1 transcriptome expression and its impact on outcome in patients treated with immune checkpoint inhibitors.

2614 Background: The immunosuppressive tumor microenvironment (TME) is a major component of resistance to immune checkpoint inhibitors (ICIs). Tryptophan catabolism is recognized as a metabolic pathway leading to immunosuppression and indoleamine 2,3-dioxygenase 1 (IDO1), an enzyme catabolizing tryptophan to kynurenine, has been investigated as a potential target. Analyzing the association of IDO1 and immune molecules in the TME could better elucidate the role of IDO1 as an immunotherapeutic strategy. Thus, we performed pan-cancer transcriptome analysis of IDO1 according to cancer types and immune molecules in the TME and evaluated survival outcomes in patients treated with ICIs based on IDO1 expression levels. Methods: Comprehensive transcriptome analysis of IDO1 and selected immune molecules in 514 patients with advanced solid tumors at the Moores Cancer Center at the University of California San Diego was performed. The rate of “High” (75-100 percentile), “Intermediate” (25-74), and “Low” (0-24) IDO1 RNA expression in each cancer type was calculated (rank compared to 735 controls). Univariate and multivariate analyses of the odds ratio (OR) for high IDO1 expression based on factors such as immune checkpoints, cancer types, microsatellite instability (MSI), and tumor mutational burden (TMB) were conducted. Additionally, progression-free survival (PFS) and overall survival (OS) from the time of ICI therapy based on IDO1 expression was compared by the Kaplan-Meier method. Multivariate analysis of survival outcomes was performed using the Cox proportional hazards model. Results: Overall, 91 of 514 patients (17.7%) were classified into “High”, 228 (44.4%) into “Intermediate”, and 195 (37.9%) into “Low” IDO1 RNA expression. High IDO1 expression was seen in uterine (54.2%), ovarian (37.2%), and lung cancer (25.0%). In multivariate analysis, high STAT1 and CD40 expression, ovarian cancer, and uterine cancer were correlated with high IDO1 expression. In patients treated with ICIs (N = 217), “High” IDO1 expression (N = 49) was associated with better PFS (HR = 0.57, 95%CI: 0.40-0.83, p = 0.003) and OS (HR = 0.52, 95%CI: 0.47-0.83, p = 0.006) than “Intermediate/Low” IDO1 expression (N = 168). Multivariate analysis incorporating age, sex, IDO1, PD-1, PD-L1, PD-L2, CTLA-4, LAG3, cancer types, TMB, and MSI revealed that IDO1 (HR = 0.28, 95%CI: 0.11-0.69, p = 0.006) and PD-1 (HR = 0.24, 95%CI: 0.09-0.65, p = 0.005) are independent predictive factors for longer OS. Conclusions: IDO1 RNA levels are high in >25% of uterine, ovarian, and lung cancers but differ from patient to patient between and within tumor types. High IDO1 levels correspond with longer PFS and OS from start of ICI therapy. These results suggest the importance of patient selection through pan-cancer molecular analysis and the potential role of IDO1 as a predictive marker for ICI therapy.

Dormancy and dormancy release in white-grained wheat (Triticum aestivum L.).

Dormancy in white-grained wheat is conditioned by the cumulative effects of several QTL that delay the onset of the capacity to germinate during ripening and after-ripening. Grain dormancy at harvest-ripeness is a major component of resistance to preharvest sprouting in wheat (Triticum aestivum L.) and an important trait in regions where rain is common during the harvest period. Breeding lines developed in Australia maintained their dormancy phenotype over multiple seasons and during grain ripening, the time between anthesis and the acquisition of the capacity to germinate, dormancy release, increased in line with the strength of dormancy. Genetic dissection of two dormant lines indicated that dormancy was due to the cumulative action of between one and three major genetic loci and several minor loci. This presents a significant challenge for breeders targeting environments with a high risk of sprouting where strong dormancy is desirable. Only around half of the difference in dormancy between the dormant lines and a non-dormant variety could be attributed to the major genetic loci on chromosomes 4A and 3A. A QTL that was mapped on chromosome 5A may be an orthologue of a minor QTL for dormancy in barley. At each locus, the dormancy allele increased the time to dormancy release during ripening. In combination, these alleles had cumulative effects. Embryo sensitivity to abscisic acid was related to the dormancy phenotype of the whole caryopsis, however, changes in concentrations of abscisic acid and gibberellins in embryo sections and de-embryonated grains during ripening and after-ripening could not be linked to the timing of dormancy release.

Orobanche foetida resistance in two new faba bean genotypes produced by radiation mutagenesis

Purpose: Broomrape produces serious damage to many legume crops and, particularly, becomes a limiting factor for faba bean (Vicia faba L.) production in the Mediterranean basin. Currently, several traditional methods of control have been developed, but none has proved to be effective for this parasite. However, breeding for resistance to this pest remains as one of the most feasible and environment-friendly methods for managing broomrape, but the mechanisms governing the interaction between the parasite and the host are not yet well understood. Therefore, we studied the behavior and molecular and enzymatic changes associated with the resistance to Orobanche foetida in faba bean mutants, which were obtained through radiation mutagenesis.Materials and methods: Three faba bean genotypes were used in this study, the variety ‘Badï’, characterized by high productivity in Orobanche-free soils and susceptibility to O. foetida, and two mutant lines P2M3 and P7M3 (derived from radio mutagenesis program), selected for their higher resistance to O. foetida in a field evaluation. The infection progress and the relative changes in the co-culture response, the enzymatic activities changes and the efficiency of the root extract stimulants from the host plant were followed and evaluated in all the genotypes.Results: Experiments showed that low induction of seed germination is a major component of resistance in these lines against O. foetida. This is confirmed by the in vitro experiments with root exudates. The parallel reduction in infection was accompanied by the continuous enhancement of the peroxidase activity, the polyphenol oxidase activity and the phenylalanine ammonia lyase activity in faba bean roots.Conclusion: These data suggest the contribution of these enzymes in faba bean resistance to O. foetida broomrape induced by the use of gamma rays. Management of Orobanche by way of crop selection, based on these enzyme systems is a possible option.

Ovipositional preferences and larval survival of annual bluegrass weevil, Listronotus maculicollis, on Poa annua and selected bentgrasses (Agrostis spp.)

AbstractThe annual bluegrass weevil (ABW), Listronotus maculicollis Kirby (Coleoptera: Curculionidae), is a serious and expanding pest of short‐cut turfgrass on golf courses in eastern North America. Increasing problems with the development of insecticide resistance in this pest highlights the need for more sustainable management approaches. Plant resistance is one of the most promising alternative strategies. Bentgrasses are the dominant grass species on golf course fairways, tees, and putting greens in the areas affected by ABW. But Poa annua L. (Poaceae), a highly invasive weed, often constitutes a large percentage of turf stands in short‐mown golf courses and is thought to be particularly susceptible to ABW. We studied resistance to ABW in four cultivars of creeping bentgrass, Agrostis stolonifera L., and two cultivars each of colonial bentgrass, Agrostis capillaris L., and velvet bentgrass, Agrostis canina L. (Poaceae), in comparison with P. annua by addressing the three major components of resistance: antixenosis (adult ovipositional and feeding preferences), antibiosis (larval survival and growth), and grass tolerance (grass damage). Our findings suggest that antixenosis/non‐preference is at least partially involved in bentgrass resistance to ABW. Even though oviposition was observed in all tested grasses, females laid significantly fewer eggs in Agrostis spp. than in P. annua. Compared to P. annua, Agrostis spp. were also less suitable for larval development with lower numbers of ABW immatures recovered and larvae weighing less and being less advanced in development. Resistance levels to ABW larvae varied significantly among Agrostis spp. and cultivars. Agrostis canina was least preferred by females for oviposition and A. stolonifera was the least suitable for larval survival and development. Agrostis spp., especially A. stolonifera, were more tolerant to ABW feeding than P. annua. Our findings suggest that reduction in P. annua and replacement with Agrostis spp., especially A. stolonifera, wherever feasible should be integral to more sustainable approaches to ABW management.

Metal-to-Multilayer-Graphene Contact—Part II: Analysis of Contact Resistance

The parasitic contact resistance between metal electrodes and multilayer graphene (MLG) is studied, and the different parameters influencing the contact resistance are investigated. A theoretical model that was developed in the companion paper is applied to typical metal–MLG structures to study the characteristics of the contact. The contributions of all of the three major components of resistance—the top and edge contacts (side and end contacts), the MLG sheet resistivity, and the metal sheet resistivity—to the total resistance are studied. The results show that the total resistance of the metal–MLG contact reduces substantially with the incorporation of edge contacts as the number of graphene layers increases. The current crowding effects are studied with and without consideration of the metal resistivity. Furthermore, the conditions where each of the three major resistance components becomes important are investigated. It is shown that the metal resistance can play an important role in determining the total resistance and current distribution in the contact. The developed model can be used in the characterization and in the design of efficient metal–MLG contact structures. It is shown that, due to the presence of edge contacts, the conventional methods of contact characterization cannot model the metal–MLG structure accurately.

Metal-to-Multilayer-Graphene Contact—Part I: Contact Resistance Modeling

Parasitic components are becoming increasingly important with geometric scaling in nanoscale electronic devices and interconnects. The parasitic contact resistance between metal electrodes and multilayer graphene (MLG) is a key factor determining the performance of MLG-based structures in various applications. The available methods for characterizing metal–MLG contact interfaces rely on a model based on the top-contact structure, but it ignores the edge contacts that can greatly reduce the contact resistance. Therefore, in the present work, a rigorous theoretical 1-D model for metal–MLG contact is developed for the first time. The contribution of the major components of resistance—the top and edge contacts (side and end contacts) and the MLG sheet resistivity—to the total resistance of the structure is included in the model. The 1-D model is compared to a 3-D model of the system, and a method for investigation and optimization of the range of validity of the 1-D model is developed. The results of this work provide valuable insight to both the characterization and design of metal–MLG contacts.

Resistance against broomrapes (Orobanche and Phelipanche spp.) in faba bean (Vicia faba) based in low induction of broomrape seed germination

Broomrapes are weedy root parasitic plants that severely constraint faba bean production. After long and extensive breeding efforts made in several countries only moderately resistant cultivars are available to farmers, being their resistance based on a combination of avoidance and resistance mechanisms. In this work we characterize the resistance mechanism of two faba bean breeding lines selected for resistance to Orobanche crenata. Mini-rhizotron experiments showed that low induction of seed germination is a major component of resistance in these lines against O. crenata, O. foetida and P. aegyptiaca. This is confirmed by in vitro experiments with root exudates. The fact that low induction of germination is similarly operative against O. crenata, O. foetida and P. aegyptiaca reinforce the value of this resistance.

Interactions of spotted stem borer Chilo partellus with wild relatives of sorghum

With 5 tablesAbstractThe levels of resistance to spotted stem borer (Chilo partellus) in sorghum are low to moderate. We therefore evaluated wild relatives of sorghum to identify accessions with high levels of resistance to this pest and studied the mechanisms of resistance. Heterosorghum (Sorghum laxiflorum), Para‐sorghum (S. australiense, S. purpureo‐sericeum, S. versicolor, S. matarankense, S. timorense, S. brevicallosum and S. nitidum) and Stiposorghum (S. angustum, S. ecarinatum, S. extans, S. intrans, S. interjectum and S. stipoideum) showed very high levels of resistance to stem borer. Chaetosorghum (S. macrospermum), four wild races of S. bicolor subsp. verticilliflorum and S. halepense were found to be susceptible. Under no‐choice conditions, egg laying was observed on all accessions, which significantly differed among the species/accessions. Accessions belonging to Stiposorghum and Para‐sorghum (S. purpureo‐sericeum, S. versicolor and S. timorense) were significantly less preferred for oviposition than the resistant control, IS 2205. Accessions belonging to Stiposorghum showed slight leaf‐feeding, but there was no deadheart formation. Although there was some damage in Para‐sorghum, very few deadhearts were formed, and a few larvae that were recovered subsequently died. In Heterosorghum, the two accessions of S. laxiflorum were highly preferred for oviposition, and up to 82% deadhearts were recorded, but the six larvae that were recovered died within a month. Accessions belonging to Eu‐sorghum showed maximum deadhearts, larval recovery and adult emergence. The results suggested that some of the wild relatives of sorghum possess high levels of resistance to C. partellus and both antixenosis and antibiosis are major components of resistance to this pest. Accessions showing high levels of resistance to stem borer can be utilized to increase the levels and diversify the bases of resistance to this pest in sorghum.

Microbial Efflux Pump Inhibition: Tactics and Strategies

Traditional antimicrobials are increasingly suffering from the emergence of multidrug resistance among pathogenic microorganisms. To overcome these deficiencies, a range of novel approaches to control microbial infections are under investigation as potential alternative treatments. Multidrug efflux is a key target of these efforts. Efflux mechanisms are broadly recognized as major components of resistance to many classes of chemotherapeutic agents as well as antimicrobials. Efflux occurs due to the activity of membrane transporter proteins widely known as Multidrug Efflux Systems (MES). They are implicated in a variety of physiological roles other than efflux and identifying natural substrates and inhibitors is an active and expanding research discipline. One plausible alternative is the combination of conventional antimicrobial agents/antibiotics with small molecules that block MES known as multidrug efflux pump inhibitors (EPIs). An array of approaches in academic and industrial research settings, varying from high-throughput screening (HTS) ventures to bioassay guided purification and determination, have yielded a number of promising EPIs in a series of pathogenic systems. This synergistic discovery platform has been exploited in translational directions beyond the potentiation of conventional antimicrobial treatments. This venture attempts to highlight different tactical elements of this platform, identifying the need for highly informative and comprehensive EPI-discovery strategies. Advances in assay development genomics, proteomics as well as the accumulation of bioactivity and structural information regarding MES facilitates the basis for a new discovery era. This platform is expanding drastically. A combination of chemogenomics and chemoinformatics approaches will integrate data mining with virtual and physical HTS ventures and populate the chemical-biological interface with a plethora of novel chemotypes. This comprehensive step will expedite the preclinical development of lead EPIs.

Interfacial resistance of the LiFePO 4-C/PEO-LiTFSI composite electrode for dry-polymer lithium-ion batteries

The interfacial resistance between the composite electrode and PEO-based solid polymer electrolyte was examined using two different symmetrical cells and AC impedance measurements in the temperature range of 30–60 °C. Of the four major resistance components identified in our previous study, three components due to the resistances of the polymer electrolyte and the charge transfer resistance between LiFePO 4-C and the electrolyte were assigned; however, one resistance component, in the medium frequency range has not yet been assigned. In this report, the medium frequency range resistance component was investigated using a symmetrical cell with composite electrodes composed of active and inactive materials (LiCoO 2, LiMn 2O 4 and SiO 2), solid polymer electrolyte, and carbon fiber as an electron conductor. The resistance was not affected by the carbon coating in LiFePO 4-C and the conductive carbon additive (VGCF). An electron blocking cell was also prepared and the resistance was measured in the temperature range of 30–60 °C to confirm the effect of the electrode thickness and the electrode composition. The resistance was not affected by the thickness, and decreased with decreasing PEO-LiTFSI electrolyte content in the composite electrode. However, no significant change in the activation energy was evident with the change in the electrode composition.

Efflux pumps expression and its association with porin down-regulation and β-lactamase production among Pseudomonas aeruginosa causing bloodstream infections in Brazil

BackgroundMulti-drug efflux pumps have been increasingly recognized as a major component of resistance in P. aeruginosa. We have investigated the expression level of efflux systems among clinical isolates of P. aeruginosa, regardless of their antimicrobial susceptibility profile.ResultsAztreonam exhibited the highest in vitro activity against the P. aeruginosa isolates studied (64.4% susceptibility), whereas susceptibility rates of imipenem and meropenem were both 47.5%. The MexXY-OprM and MexAB-OprM efflux systems were overexpressed in 50.8% and 27.1% of isolates studied, respectively. Overexpression of the MexEF-OprN and MexCD-OprJ systems was not observed. AmpC β-lactamase was overexpressed in 11.9% of P. aeruginosa isolates. In addition, decreased oprD expression was also observed in 69.5% of the whole collection, and in 87.1% of the imipenem non-susceptible P. aeruginosa clinical isolates. The MBL-encoding genes blaSPM-1 and blaIMP-1 were detected in 23.7% and 1.7% P. aeruginosa isolates, respectively. The blaGES-1 was detected in 5.1% of the isolates, while blaGES-5 and blaCTX-M-2 were observed in 1.7% of the isolates evaluated. In the present study, we have observed that efflux systems represent an adjuvant mechanism for antimicrobial resistance.ConclusionsEfflux systems in association of distinct mechanisms such as the porin down-regulation, AmpC overproduction and secondary β-lactamases play also an important role in the multi-drug resistance phenotype among P. aeruginosa clinical isolates.

Friction and resistance to sliding in orthodontics: A critical review

Despite the emphasis it now receives in the marketing of self-ligating brackets, friction is not the major component of resistance to sliding in clinical treatment. Laboratory studies show that binding of the wire against the corners of the bracket, which occurs soon after tooth movement begins, is much more important than previously thought, and that notching of the archwire, which temporarily stops movement, can occur. Clinical studies support the view that resistance to bodily tooth movement by sliding has little to do with friction and, instead, is largely a binding-and-release phenomenon that is about the same with conventional and self-ligating brackets. The limited clinical trial data available now do not support the contention that treatment time is reduced (presumably because of lower friction) with self-ligating brackets.

Clinical implications of multiple drug resistance efflux pumps of pathogenic bacteria

Resistance of microorganisms to many classes of antibiotics and other drugs is a major problem throughout the world. This antimicrobial resistance can be mediated by various mechanisms such as enzymatic inactivation of the drug, alteration of the target and decreased intracellular concentration of the antimicrobial. The latter mechanism is mediated by either decreased influx or increased efflux or a combination of both. Recently, efflux has become increasingly recognized as a major component of resistance. Some efflux pumps selectively extrude specific antibiotics such as macrolides, lincosamides and/or streptogramins and tetracyclines, whereas others, referred to as multiple drug resistance pumps, expel a variety of structurally diverse anti-infectives with different modes of action. This phenomenon, whereby a single transporter is able to recognize and transport multiple antimicrobials with no common structural homology, was first described in the late 1980s in higher eukaryotes where P-glycoprotein was found to play a role in resistance to anti-cancer chemotherapeutic agents. Later, it became apparent that efflux systems were also present in microorganisms. Efflux pump inhibitors offer considerable promise as therapeutic agents, as they should restore the activity of standard antibiotics.

Effect of O6-(4-bromothenyl)guanine on different temozolomide schedules in a human melanoma xenograft model.

The DNA repair protein O(6)-alkylguanine DNA alkyltransferase (ATase) is a major component of resistance to treatment with methylating agents and nitrosoureas. Inactivation of the protein, via the administration of pseudosubstrates, prior to chemotherapy has been shown to improve the latter's therapeutic index in animal models of human tumours. We have also shown that rational scheduling of temozolomide, so that drug is administered at the ATase nadir after the preceding dose, increases tumour growth delay in these models. We now report the results of combining these two approaches. Nude mice bearing A375M human melanoma xenografts were treated with vehicle or 100 mg/kg temozolomide ip for 5 doses spaced 4, 12 or 24 hr apart. Each dose was preceded by the injection of vehicle or 20 mg/kg 4BTG. All treatments resulted in significant delays in tumour quintupling time compared with controls: by 6.2, 5.9 and 16.8 days, respectively, for 24-, 12- and 4-hourly temozolomide alone and by 22.3, 21.3 and 22.1 days, respectively, in combination with 4BTG. Weight loss due to TMZ was unaffected by the presence of 4BTG. This was of the order of 6.2-10.6% with 24- and 12-hourly administration and 17.4-20.1% (p < 0.0001) with 4-hourly treatment. In our model, combining daily temozolomide with 4-BTG confers increased antitumour activity equivalent to that achieved by compressing the temozolomide schedule but with less toxicity. Using temozolomide schedule compression with 4-BTG does not improve on this result, suggesting that ATase inactivation with pseudosubstrates is a more promising means of enhancing the activity of temozolomide than compressed scheduling.

Altered Acetylcholinesterase Confers Organophosphate Resistance in the Olive Fruit Fly Bactrocera oleae

An organophosphate-resistant strain of the olive fruit fly Bactrocera oleae, the most important pest for olive orchards worldwide, was obtained by laboratory selection with dimethoate. Resistance mechanisms were investigated in comparison with the colonized parental strain and a field population collected from the same area after 12 years of continuous dimethoate-based insecticide pressure. Combined biochemical and bioassay data suggested that, although esterase and/or glutathione S-transferase metabolic pathways were present and active against dimethoate, they were not selected for and did not have a major role in resistance. There was no evidence of increased oxidase activity in the resistant strains or significant synergism of dimethoate toxicity by piperonyl butoxide; thus, oxidative metabolism was not a major component of resistance. An altered acetylcholinesterase (AChE) with poorer catalytic efficiency for the substrate acetylthiocholine iodide and 5- to 16-fold lower sensitivity to inhibition by omethoate was the major resistance mechanism. Dimethoate selected the insensitive AChE allele(s) in the resistant insects, which were also insensitive to paraoxon, but the altered AChE mechanism conferred negative cross-resistance to the carbamate propoxur.

Accumulation of 3-deoxyanthocyanidin phytoalexins and resistance to Colletotrichum sublineolum in sorghum

3-Deoxyanthocyanidins are the principal phytoalexins that accumulate in sorghum in response to fungal infection. Two cultivars which differed in their reaction to Colletotrichum sublineolum, the pathogen causing the anthracnose disease in sorghum, were examined for their phytoalexin response and expression of defense-related genes. In the incompatible interaction, fungal development in the host was contained during early stages of pathogenesis. When compared to the susceptible cultivar, defense responses in the resistant cultivar were characterized by a greater and faster accumulation of phytoalexins and an earlier induction of defense-related genes encoding chalcone synthase and pathogenesis-related protein PR-10. In the compatible interaction, the pathogen was able to colonize the host with the proliferation of primary and secondary hyphae. In addition to the quantitative and timing differences, there were qualitative differences between the cultivars in their phytoalexin response. Thus, the resistant cultivar accumulated a complex phytoalexin mixture, including luteolinidin and 5-methoxyluteolinidin, neither of which was produced by the susceptible cultivar following fungal inoculation. These compounds were shown previously to exhibit higher fungitoxicity than other phytoalexin components in sorghum. Our results demonstrate that 3-deoxyanthocyanidin phytoalexins represent major components of resistance to C. sublineolum in sorghum.

The design of pig stunning tong electrodes—A review

The effectiveness of current electrical stunning systems for pigs is discussed and the need for improvements in the design and construction of stunning tongs and electrodes are explored. A review of existing stunning tong electrodes for use with free standing or restrained pig is discussed. The potential problems with existing systems are highlighted as: (1) the profile of the pigs head precludes the application of existing electrodes in the correct position; (2) the small area of contact enhances carbon build-up which increases electrical impedance; (3) the electrodes are easily tarnished with few cleaning tools provided. Good tong positions that span the brain are described as between the eye and ear on each side of the head, below the ear on each side of the head or, diagonal application between the top and bottom of the head. The notional contact impedance is the major component of resistance to current flow within the stunning system. The proposed use of different electrode designs and constructional material is investigated. The effect of the introduction of the fail-safe device would be to heighten the interest in contact impedance within the plant and that could ensure that the investigation of different electrodes is explored at least at plant level.

PLATIN (Plant-ATmosphere INteraction) I: A model of plant-atmosphere interaction for estimating absorbed doses of gaseous air pollutants

A PLant-ATmosphere INteraction model (PLATIN) was developed for estimating air pollutant absorbed doses under ambient conditions. PLATIN is based on the canopy energy balance combined with a gas transport submodel. The model has three major resistance components: (1) a turbulent atmospheric resistance R ah(z m) that describes the atmospheric transport properties between a measurement height above the canopy and the conceptual height z = d + z 0m which represents the sink for momentum according to the big-leaf concept; (2) a quasilaminar layer resistance R b, A that quantifies the way in which the transfer of sensible heat and matter (e.g. latent heat, ozone) differs from momentum transfer; (3) a canopy or surface resistance R c,A that describes the influences of the plant/soil system on the exchange processes. Soil water content is simulated by a Force-Restore model. By a simple interception submodel precipitation and dew are partitioned into intercepted water and water reaching the soil surface. PLATIN can be run in a prognostic or a diagnostic mode. It is also intended for on-line use in air quality monitoring networks.

Leaf profile of maize resistance factors to European corn borer,Ostrinia nubilalis

The feeding preference of European corn borer larvae for immature whorl tissue of maize was examined by conducting leaf bioassays and quantifying resistance factors along the length of mid-whorl leaves from the maize synthetic BS9(C4) developed by recurrent selection for resistance. Potential resistance factors that were quantified included percent foliar nitrogen, gravimetric determination of soluble metabolites and fiber, soluble phenolics and hydroxamic acids, cell-wall-bound phenolics, leaf toughness, and UV absorbance of the epidermal cell wall determined by microspectrophotometry. Larvae consumed immature tissue at a higher rate than more mature tissue outside of the whorl, despite higher levels of DIMBOA in immature tissue. Consumption rate was highly negatively correlated with epidermal cell wall absorbance and leaf toughness. Fiber content and phenolic fortification of cell walls are proposed as the major resistance components that influence European corn borer feeding preference within the resistant synthetic BS9(C4).

Field and glasshouse studies on components of resistance to root fly attack in swedes

SUMMARYField trials in two years indicated that egg‐laying antixenosis was the major component of resistance in swede cvs Angus and Melfort against root flies (Delia floralis and D. radicum). Between four and eight times as many D. floralis eggs were laid on the susceptible cv. Doon Major as on the resistant cv. Angus. The degree of antixenosis effective against D. radicum was more variable in 1985, due to low numbers of adult flies, but in 1986, when adult fly numbers were higher, D. radicum laid 34 times as many eggs on susceptible cv. Sator Øtofte as on Angus.Root antibiosis against larval feeding is a second but less important component of resistance against D. floralis. In egg inoculation tests, 1.3‐2.0 times more D. floralis pupae developed on Doon Major than on Angus or Melfort. Larval feeding on resistant cultivars was restricted to surface root tissue only, compared with deeper tunnelling on susceptible cultivars. Tolerance to root damage may also occur under certain conditions. Although increased dry matter content was significantly correlated with root antibiosis, its effect on larval feeding was apparently not due to increased tissue hardness. It seems likely that chemical differences in the outer root tissues influence larval feeding and development.