Fenarimol-resistant isolates ofPenicillium italicum with cross-resistance to imidazole and triazole fungicides which inhibit ergosterol biosynthesis were tested for their sensitivity to fenpropimorph. Radial growth tests on PDA showed that the isolates (n=6) lacked cross-resistance to fenpropimorph or displayed enhanced sensitivity to the fungicide (negatively correlated cross-resistance). Control of blue mold decay of oranges incited by the wild-type isolate could be achieved by dipping fruits in suspensions of fenpropimorph at a concentration of 100 mg ml–1. Decay of oranges incited by the fenarimol-resistant isolates was controlled at the same or at a lower concentration (30 mg ml–1), thus showing that the normal or increased sensitivity to fenpropimorph is also expressed under in vivo conditions.Samenvatting Fenarimol-resistente isolaten vanPenicillium italicum met kruisresistentie tegen imidazool-en triazoolfungiciden die de ergosterolbiosynthese remmen, werden getoetst op hun gevoeligheid voor fenpropimorf. Radiale groeiproeven op PDA toonden aan dat de isolaten (n=6) geen kruisresistentie bezaten met fenpropimorf of een verhoogde gevoeligheid voor het middel vertoonden (negatief gecorreleerde kruisresistentie). Op sinaasappels konPenicillium-rot, veroorzaakt door het wild-type bestreden worden door middel van een dompelbehandeling met fenpropimorf bij een dosering van 100 g ml–1). Bestrijding van rot veroorzaakt door fenarimil-resistente isolaten werd verkregen bij dezelfde of een lagere dosering (30 g ml–1); aldus werd aangetoond dat de normale of verhoogde gevoeligheid voor fenpropimorf ook in vivo tot uiting komt. 相似文献
Introgression of trichome-mediated insect resistance from the wild speciesSolanum berthaultii has become a major focus of the potato improvement program at Cornell University during the past twelve years. Several quantitative characters are involved in this resistance which is effective against a wide range of pest types. Correlative biochemical assays have been developed to assay specific components of the resistance, and the effects of the resistance on the target pests have been studied. Quantitative laboratory assays and specific measurements of insect behavior and biology have increased the precision of selection and enable the investigation of the genetic control of the resistance.We are currently using restriction fragment length polymorphisms (RFLPs) for genetic mapping of factors controlling the trichome traits fromS. berthaultii. Backcrosses to both the wild and the cultivated species parents have been evaluated for phenotypes contributing to the resistance mechanism, including trichome density, sucrose ester and polyphenol oxidase production by the trichomes, and the enzymatic browning reaction responsible for insect entrapment. Genetic maps are being developed for these progenies, using RFLP markers previously mapped in potato. Field and greenhouse trials under insect infestations are also being conducted with the mapping progeny. Our goal is to locate genes responsible for quantitative insect resistance by correlating RFLP variation at mapped loci with the trichome phenotypes and insect resistance. Genetic markers for these traits will be useful in transfer of the effective wild chromosomal segments into and among tetraploid potatoes, and for a better understanding of the resistance mechanism. 相似文献
Conventional ways to control aphid vectors on potato crops rely essentially on cultural and chemical methods. The extensive use of insecticides, too often applied regardless of real needs and consequences, has resulted in more and more failures in both controlling aphids and virus spread. This paper stresses the need to introduce more rationale in the operation of existing methods by improving the efficiency of some of them like forecasting systems, to assess the potential of others like fertilization and semiochemicals and to put most efforts on resistant cultivars so that integrated pest management can be operated in the near future. 相似文献
Chicks and chickens maintained under commercial conditions were vaccinated against Newcastle Disease via drinking water. Prior and after different times of vaccination blood samples were drawn from different numbers of birds and checked for HI antibodies. The modes of distribution of the antibody titers within the random sample were assayed. The following results were obtained:
1. 1. On the basis of the distribution of the serum titers can be concluded whether the antibody level within a flock is increasing or decreasing.
◦ —A right steep asymmetry can be observed up to 20 days post vaccination.
◦ —In the phase of maximal antibody levels an almost symmetric distribution of the titers is present.
◦ —In later times (more than three weeks p. vacc.) the distribution shows a left steep asymmetry (Poisson distribution).
2. 2. A poisson distribution is also observable during the elimination of maternal antibodies of chicks until complete elimination.
3. 3. The mode of distribution of the HI titers in sera of day-old chicks correlates with the mode of distribution of the dams. Therefore, conclusions are possible from the status of the chicks to the dams and reverse.
4. 4. Factors which interfere with the mode of distribution are:
◦ —Two or more peaks after vaccination of chickens. This indicates an uneven immune response within the flock.
◦ —Distributions with several peaks may also occur if flocks are composed of day-old chicks from parent flocks with different levels of antibody titers.
Résumé
Des poulets et des poussins maintenus dans un élevage conventionnel furent vaccinés contre la maladie de Newcastle par un vaccin administré dans l'eau de boisson. Avant et à différents temps après vaccination, des échantillons de sang furent prélevés sur un certain nombre de poussins et les anticorps inhibants de l'hémagglutination furent recherchés. Les modes de la distribution des titres en anticorps pour les échantillons pris au hasard furent recherchés. Les résultats suivants furent obtenus:
1. 1. Sur la base de la distribution des titres sériques, on peut conclure si le taux en anticorps à l'intérieur d'une population a augmenté ou diminué.
◦ —Une courbe asymétrique avec un pic déplacé vers la droite peut être observée 20 jours après la vaccination.
◦ —La phase correspondant au taux maximal en anticorps présente une distribution presque normale.
◦ —Plus tard, (au-delà de 3 semaines après la vaccination), la distribution apparaît asymétrique avec un déplacement vers la gauche (distribution de Poisson).
2. 2. Une distribution de Poisson peut aussi être observée au moment de l'élimination des anticorps d'origine maternelle chez des poussins jusqu'à complète élimination.
3. 3. Le mode de distribution des titres en anticorps inhibant l'hémagglutination dans des sérums de poussins d'un jour correspond au mode de distribution observé chez les mères. Des conclusions peuvent donc être faites à partir de l'état immunologique des poussins vis-à-vis des mères et viceversa.
4. 4. Les facteurs qui peuvent intervenir dans le mode de distribution sont:
◦ —Deux pics ou plus après la vaccination des poussins. Ceci indique qu'il existe une réponse immunitaire inégale dans la population.
◦ —Des distributions avec plusieurs pics peuvent être également observées si les populations sont composées de poussins de un jour provenant de populations parentales ayant des taux différents de titres en anticorps.
Nine different strains of the two-spotted spider miteTetranychus urticae Koch (Acari: Tetranychidae) were collected on cotton from Adana, Antalya, Izmir, Manisa and Urfa in Turkey. Their responses
to bifenthrin were investigated using conventional bioassay and biochemical assays. LC50 and LC90 values of bifenthrin were determined for all strains by using a residual bioassay with a petri dish-spray tower. Resistance
ratios were determined by comparing the samples with a standard susceptible strain, GSS. The resistance ratios of the strains
ranged from <1 to 669-fold (at LC50). Of the investigated field strains, only three (two from Adana and one from Urfa) were resistant to bifenthrin. There was
a correlation between esterase enzyme activity and bifenthrin resistance according to polyacrylamide gel electrophoresis and
microtiter plate assays in the three resistant strains.
http://www.phytoparasitica.org posting May 17, 2005. 相似文献
As plants mature it has been observed that some become more resistant to normally virulent pathogens. The ability to manifest the Age-Related Resistance (ARR) response in Arabidopsis to Pseudomonas syringae pathovars tomato (Pst) coincided with the transition to flowering in plants both delayed and accelerated in the transition to flowering. ARR was also associated with a change in PR-1 gene expression, such that young plants expressed PR-1 abundantly at 3 days post inoculation (dpi) while mature plants expressed much less. The Arabidopsis ARR response requires SA accumulation via isochorismate synthase (ICS1) [24]. ICS1 was expressed one dpi with virulent and avirulent Pst in both young and mature plants. The ARR response was also effective versus avirulent Pst providing an additional 4-fold limitation in bacterial growth. Arabidopsis ARR was found to be ineffective against two necrotrophs, Erwinia carotovora subspecies carotovora (bacterium) and Botrytis cinerea (fungus) and one obligate biotroph, Erysiphe cichoracearum (fungus). However, mature wild type, SA-deficient sid2 and NahG plants supported little growth of the obligate biotrophic oomycete, Peronospora parasitica. Therefore ARR to P. parasitica appears to be SA-independent, however the level of ARR resistance was somewhat reduced in these mutants in some experiments. Thus, there may be numerous defence pathways that contribute to adult plant resistance in Arabidopsis. 相似文献
An isolate of Trichoderma harzianum Rifai from an infected cacao pod produces and secretes nonanoic (pelargonic) acid into a liquid culture medium. Nonanoic acid (NA) was very inhibitory to spore germination and mycelial growth of two cacao pathogens, Crinipellis perniciosa Stahel and Moniliophthora roreri Cif. H.C. Evans. It was highly active causing 75% inhibition of spore germination in an in vitro assay at a rate as low as 0.09 μM for M. roreri and 0.92 μM for C. perniciosa. Mycelial growth was comparatively less sensitive to inhibition, but still there was a 75% reduction in growth with 0.62 μM in M. roreri and 151 μM NA in C. perniciosa. In contrast, NA did not affect Trichoderma mycelial growth or spore germination at concentrations that were inhibitory to the pathogens. 6-pentyl-α-pyrone was also produced and secreted into the medium by T. harzianum, however; it was not antagonistic to the cacao pathogens. Although a number of metabolites produced by Trichoderma spp. have been identified in the past, this is the first report of NA production and secretion by any Trichoderma. The results suggest that NA may play a role in the successful use of some Trichoderma spp. isolates in the biocontrol of fungal diseases of plants. 相似文献
A phytotoxic protein that evokes the typical symptoms of Verticillium wilt disease in seedlings of Gossypium hirsutum L. (Upland cotton) was isolated from culture filtrates of Verticillium dahliae. The protein was purified by ammonium sulfate precipitation, Sephadex-G100 fractionation, and native PAGE. The 18.5 kDa protein, designated VD18.5, appears to be a single subunit protein with an isoelectric point between 3 and 5. VD18.5 induces symptoms of leaf dehydration, chlorosis, necrosis and stem discoloration in seedlings of the disease susceptible cotton cultivar Siokra 1–4. The LD50 of VD18.5 on protoplasts of Siokra 1–4 was 18 μg mL−1. VD18.5 had no noticeable effect on Pima S-7, which is a disease resistant cultivar. Phytotoxic activity was partially destroyed at high temperature and was abolished by digestion with proteinase K. Mass spectrometry fingerprinting and protein sequence data from VD18.5 yielded no significant matches when submitted to the Mascot search engine and NCBI non-redundant protein databases, respectively. These results suggest that VD18.5 is a novel protein that may be involved in the development of some of the symptoms associated with Verticillium wilt disease in the cotton plant. 相似文献
