The monoterpenoid (S)-carvone was shown earlier to induce glutathione S-transferase (GST) activity and to attenuate necrotic lesion formation in Tobacco mosaic virus (TMV) inoculated, hypersensitively reacting tobacco Xanthi-nc plants. To explore structure-activity relationships, three monoterpenes and five monoterpenoids were tested for their ability to induce increased GST activity in tobacco leaf discs. (S)-Carvone proved to be the most potent inducer. (S)-Carvone treatments markedly up-regulated the expression of several tobacco GST genes belonging to the phi, tau and theta classes, particularly in the case of tau class GSTs. Furthermore, TMV inoculation slightly induced the transcript abundance of the GSTT2 gene. The expression of three catalase (CAT) genes was also examined in (S)-carvone-treated tobacco leaf discs. The expression of CAT1 was not influenced by (S)-carvone treatments, whereas that of CAT2 was significantly repressed. (S)-Carvone very weakly induced the transcription of the CAT3 gene. The effect of the opposite enantiomer, (R)-carvone on the expression of GST and CAT genes was similar to that of (S)-carvone. Our results suggest that the antioxidative reactions catalyzed by tau and theta class GSTs contribute to the attenuation of necrotic disease symptoms in TMV-inoculated tobacco plants.
Authors:F. M. Momen, S. A. A. Amer, and A. M. Refaat
The deterrent and toxic effect of two essential oils, Majorana hortensis. Moench and Rosma- rinus officinalis L. on the two tetranychid mites Tetranychus urticae Koch and Eutetranychus orientalis (Klein) were studied under laboratory conditions. Both materials used were more potent for E. orientalis than against T. urticae with a significant increase in repellency. Leaf discs treated with increasing concentrations of the two oils showed increased mortality of both spider mites and reduction in the total numbers of eggs laid. This result could be due to the oil of the higher oxygenated compounds content that was more effective in this respect.
populations were tested for their ability to transmit a
Tomato spotted wilt virus
(TSWV) isolate from South Bulgaria (GD07) originating from tobacco. The thelytokous population originated from leek and the arrhenotokous population from tobacco. The two populations were analyzed separately under laboratory conditions and the offspring of unmated females of each population were tested. The transmission efficiency of adult
was tested with petunia leaf disc assays. The investigation showed that the thelytokous population and the resulting offspring, which also consisted of females, were not able to transmit the TSWV isolate. The arrhenotokous population and its offspring differed in transmission efficiency of GD07. The transmission rate of the arrhenotokous population was about 20%, with male individuals exhibiting higher transmission rate than females. The offspring of the arrhenotokous population, consisting only of males, transmitted TSWV GD07 with 93% efficiency.
Authors:H. HUSSEIN, M. ABOU-ELELlA, S. A. A. AMER, and F. M. MOMEN
Two parts of the plant
Capparis aegyptia, leaves and fruits, were extracted successfully with 4
different solvents. These solvents namely n-hexane, diethyl ether, ethyl
acetate and ethanol. These extracts were tested for their toxicity against eggs
and adult females of the two-spotted spider mite, Tetranychus urticae Koch.
Extracts of both parts of the plant, prepared from various solvents were
affected the behavior, toxicity and fecundity of females under laboratory
conditions. Ethyl acetate extract of leaves and fruits was the most potent
extract tested against eggs and adult females of T. urticae. In contrast,
ethanol extract of fruits was the least effective extract against both tested
stages. The egg stage was less susceptible to most different extracts of both
parts of C. aegyptia. Leaf discs treated with LC50 concentration of various
extracts showed a high percentage of repellency in case of ethanol extract from
leaves and fruits (86.67 and 96.42%), respectively. Treated females with LC50
concentration of different extracts showed a higher remarkable percentage of
mortality as well as a reduction in the total number of eggs laid during 15
days with fruit extracts than that with leaves extract.
The antifeedant activities of methanolic extracts made from seven plant species (Abutilon theophrasti Medic., Ajuga chamaepitys (L.) Schreb., Amorpha fruticosa L., Matricaria chamomilla L., Matricaria inodora L., Tanacetum vulgare L. and Tilia cordata Mill.) were assessed in the laboratory at 0.5% and 5% dosages against Colorado potato beetle (Leptinotarsa decemlineata Say) larvae. Three h and 24 h dual-choice and 3 h no-choice feeding bioassays were carried out with potato (Solanum tuberosum L.) leaf discs. Furthermore, during the no-choice test direct observations on larval behaviour were performed to help to distinguish the mode of action which underlies inhibition of feeding. At a dosage of 0.5% no plant extract deterred feeding of larvae. At 5% Matricaria inodora (and our standard Ajuga chamaepitys with well-known antifeedant properties) was the most potent antifeedant of the seven extracts tested. Antifeedant indexes and results of the behavioural observations suggest that M. inodora acts as a sensory mediated feeding deterrent, rather than as a toxin.
Authors:Allen Xue, Yuanhong Chen, Harvey Voldeng, Marc Savard, and Xuling Tian
A strain of
, ACM941 (ATCC #74447) was evaluated for its antibiosis to
G. zeae in vitro
and for controlling of fusarium head blight (FHB) under both greenhouse and field conditions, in comparison to the registered fungicide Folicur (tebuconazole). ACM941 reduced the mycelial growth of the pathogen by 53% in dual culture and completely suppressed the macroconidium germination of
in coculture for 6 hours. ACM941 reduced the perithecium production by more than 99% in leaf disc assay, 23–57% on debris, and 36–70% on infested kernels. When sprayed onto wheat heads prior to inoculation with
, ACM941 significantly reduced infected spikelets (IS) by 58–71% and fusarium damaged kernels (FDK) by 59-73% compared to the untreated disease control. Under the simulated natural epidemic conditions during 2005–2007, ACM941 reduced IS by 44–51%, FDK by 33–68%, and deoxynivalenol (DON) in grains by 10–28%. ACM941 was similar to Folicur in reducing the mycelial growth, spore germination, and perithecium production of
, but was less effective than Folicur in reducing IS, FDK, and DON in the field. Results of this research suggest that ACM941 is an effective antagonist against
and may be used as an alternative of chemical fungicides in an integrated FHB management program.
Authors:S. Tonti, G. Alvisi, A. Pisi, P. Nipoti, and A. Prodi
Zymoseptoria tritici, a globally distributed pathogen, is responsible of Septoria tritici blotch (STB), one of the most damaging wheat diseases. In Italy the incidence of STB has increased during the past few years. The presence of Z. tritici on flag leaves of susceptible durum wheat plants, cultivar San Carlo, after a single artificial inoculation with two inoculum concentrations at different vegetative stages has been evaluated in the plain of Bologna (North of Italy), in a two year field study (2012–2013). The pathogen presence was also assessed in natural infection conditions after a fungicide application in the second year (2013). The results obtained, by visual examination (Incidence, Disease Severity) and DNA quantification by Real time PCR, demonstrated that BBCH 39 (flag leaf stage) is the most susceptible vegetative stage, independently of inoculum concentration and climatic conditions. A good correlation between Disease Severity and DNA quantity was observed in either sampling methods, entire flag leaves and flag leaf discs. Thereafter the most suitable period to obtain the best crop protection with only one fungicide treatment is the flag leaf stage.
The direct toxicity of three essential oils to females of the two spotted spider mite, Tetranychus urticae Koch, was tested in the laboratory. Wheat germ oil (Triticum vulgare Vill) was the most toxic essential oil to females of T. urticae, while clove oil (Eugenia caryophyllata Thumberg) was the least toxic one (LC50=0.995 and 2.82%, LC90=3.08 and 16.66%), respectively. Leaf discs treated with increasing concentrations of eucalyptus (Eucalyptus glabulus Labill.) and wheat germ oils showed a high percentage of repellency (90–100%), respectively. The oviposition deterrent indices (ODI) of eucalyptus and wheat germ oils were ranged (22–100) for T. urticae at concentration (1–4%), while this value was between (5–35%) in case of clove oil at the same above concentrations. Females of T. urticae suffered a significantly depression in reproduction when fed on painted kidney bean leaves with (1–4%) concentrations of each oil used in our studies. In contrast, at 0.25 and 0.5% concentrations, no significant differences was recorded between the total number of eggs deposited on treated leaves and control ones. Also, a high percentage of T. urticae mortality was recorded for wheat germ and clove oils during 10 days.