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1.
The development of insecticidal resistance in diamondback moth (DBM) Plutella xylostella has immediate implications for its management. In this study, we examined the mode of inheritance of Indoxacarb resistance in P. xylostella. The indoxacarb-resistant strain (Px-R) was obtained through continuous laboratory selection with increasing doses of indoxacarb in each generation. At the 14th generation of selection, the resistance ratio of Px-R strains was 238 over the susceptible strain (Px-S). The mode of inheritance to Indoxacarb in P. xylostella was examined performing standard reciprocal crosses between Px-R and Px-S and response of Px-R, Px-S and F1 hybrid progenies to Indoxacarb through leaf dip bioassay. The degree of dominance (D) and heritability (h) of F1 hybrid progeny ranged from ?0.001 to 0.0012 and 0.499 to 0.506, respectively. The Indoxacarb resistance was appeared to be autosomal and inherited as a semi-dominant trait. The Px-R strain of P. xylostella showed little cross resistance to cypermethrin and there was no cross resistance to other pesticides viz., chlorpyrifos, spinosad, karanjin, xentari (Bta-Cry1C) and MVP-II (Cry1Ac). Since the Indoxacarb resistance inherited as a semi-dominant trait in P. xylostella, the sub lethal doses and frequent use of indoxacarb should be avoided for the management of P. xylostella. Moreover, Px-R of P. xylostella showed positive cross resistance to synthetic pyrethroids (cypemethrin), therefore indoxacarb and synthetic pyrethroids should not be recommended together for management of P. xylostella.  相似文献   

2.
Psytallia concolor (Szépligeti) is a koinobiont endoparasitoid of many Tephritidae larvae, including Bactrocera oleae (Rossi), and has been used in Mediterranean areas for biological control of olive fruit fly by inundative release. The present study evaluates the influence of olive fruit variety (Amfissis, Arbequina, Branquita de Elvas, Carolea, Kalamon, Koroneiki, Leccino, Manzanilla, Mastoidis, Moroccan Picholine and Picholine) on P. concolor parasitism efficiency and performance in the field during two successive years. The results showed that the percentage of parasitism was significantly higher (>30%) in Mastoidis and Koroneiki (light-weight varieties <1.5 g) than Leccino which has a medium fruit weight, followed by Amfissis, Moroccan Picholine, Picholine and Branquita de Elvas. Only Manzanilla among large weight varieties, exhibited high percentage of parasitization (42.72%) during 2013. The mean weight of the pupae (>4.21 mg) as well as the length of the developed adult parasitoids (>3.5 cm) in Mastoidis and Manzanilla were significantly higher than these individuals developed from other varieties such as Koroneiki and Kalamon. Finally, the optimal host fruit for P. concolor development seems to be Mastoidis variety with great biological parameters and percentage of parasitism.  相似文献   

3.
Infection by Pyrenophora teres f. teres (Ptt) or P. teres f. maculata (Ptm), the causal agents of the net and spot forms of net blotch of barley, respectively, can result in significant yield losses. The genetic structure of a collection of 128 Ptt and 92 Ptm isolates from the western Canadian provinces of Alberta (55 Ptt, 27 Ptm), Saskatchewan (58 Ptt, 46 Ptm) and Manitoba (15 Ptt, 19 Ptm) were analyzed by simple sequence repeat (SSR) marker analysis. Thirteen SSR loci were examined and found to be polymorphic within both Ptt and Ptm populations. In total, 110 distinct alleles were identified, with 19 of these shared between Ptt and Ptm, 75 specific to Ptt, and 16 specific to Ptm. Genotypic diversity was relatively high, with a clonal fraction of approximately 10 % within Ptt and Ptm populations. Significant genetic differentiation (PhiPT = 0.230, P = 0.001) was found among all populations; 77 % of genetic variation occurred within populations and 23 % between populations. Lower, but still significant genetic differentiation (PhiPT = 0.038, P = 0.001) was detected in Ptt, with 96 % of genetic variation occurring within populations. No significant genetic differentiation (PhiPT = 0.010, P = 0.177) was observed among Ptm populations. Isolates clustered in two distinct groups conforming to Ptt or Ptm, with no intermediate cluster. The high number of haplotypes observed, combined with an equal mating type ratio for both forms of the fungus, suggests that P. teres goes through regular cycles of sexual recombination in western Canada.  相似文献   

4.
Bacterial blight (BB) of rice caused by Xanthomonas oryzae pv. oryzae (Xoo), remains a major production constraint in rice cultivation especially in irrigated and rainfed lowland ecosystems in India. The pathogen is highly dynamic in nature and knowledge on pathotype composition among the Xoo population is imperative for designing a scientific resistance breeding program. In this study, four hundred isolates of Xoo collected from diverse rice growing regions of India were analyzed for their virulence and genetic composition. Virulence profiling was carried out on a set of differentials consisting of 22 near isogenic lines (NILs) of IR24 possessing different BB resistance genes and their combinations along with the checks. It was observed that different NILs possessing single BB resistance gene were susceptible to about 59–94% of the Xoo isolates except IRBB 13 (containing BB resistance gene xa13), which showed susceptibility to about 35% of the isolates. Based on the reaction of the Xoo isolates on the differentials, they were categorized into 22 pathotypes. Among the 22 pathotypes, IXoPt-1 and IXoPt-2 were least virulent and IXoPt # 18–22 were highly virulent. Pathotype IXoPt-19 which was virulent on all single BB resistance genes except xa13 constituted the major pathotype (22.5% isolates) and was widely distributed throughout India (16 states). This was followed by pathotype IXoPt-22 (17.25%) which was virulent on all the NILs possessing single BB resistance genes. Molecular analysis was carried out using two outwardly directed primers complementary to sequence of IS1112, a repetitive element of Xoo. A high level of genetic polymorphism was detected among these isolates and the isolates were grouped into 12 major clusters. The data indicated complex nature of evolution of the Xoo pathotypes and there was no strong correlation between pathotypes and genetic clusters as each genetic cluster was composed of Xoo isolates belonging to different pathotypes. The study indicated that none of the single BB resistance genes can provide broad spectrum resistance in India. However, two-gene combinations like xa5 + xa13 and different 3 or 4 genes combination like Xa4 + xa5 + xa13, Xa4 + xa13 + Xa21, xa5 + xa13 + Xa21 and Xa4 + xa5 + xa13 + Xa21 are broadly effective throughout India.  相似文献   

5.
Studies were undertaken on the effects of temperature (14/10 °C and 22/17 °C day/night) and plant age (15, 23, 31 and 40 day-old-plants) on the severity of downy mildew (Hyaloperonospora parasitica) on oilseed Brassica cultivars (temperature: Brassica juncea Montara, B. napus Atomic, ATR-Hyden, Hyola 432, Hyola 450 TT, Thunder TT; plant age: B. juncea Dune, B. napus Surpass 402 and Hyola 450 TT). For temperature studies, there were significant (P?<?0.001) effects of temperature, cultivar, and cultivar x temperature interaction. On cotyledons of susceptible cultivars (B. napus Hyola 450 TT and Thunder TT), plants were symptomatic at 22/17 °C by 48 h post inoculation (hpi) and with abundant sporulation evident by 72 hpi, and with all cotyledons of B. napus Thunder TT collapsed by 7 days post inoculation (dpi). However, at 14/10 °C, there were no symptoms on the same cultivars until 5 dpi, and sporulation only observed at 7 dpi. Percent disease index values (DI%) at 22/17 °C of B. juncea Montara and B. napus ATR-Hyden, Hyola 432, Atomic, Hyola 450 TT and Thunder TT were 4.5, 49.0, 51.4, 65.8, 86.3 and 96.0, respectively, with all except B. juncea Montara having significantly lower (P?<?0.001) disease at 14/10 °C with DI% values of 2.8, 30.4, 27.9, 31.1, 44.4 and 76.4, respectively. For plant age studies, there were significant (P?<?0.001) effects of plant age, cultivar, and cultivar x plant age interaction. DI% was significantly higher at 15 compared to 40 day-old-plants (dop) across all cultivars. B. juncea Dune showed greatest resistance, particularly on 40 dop, with DI% values of 25.8, 24.6, 22.9 and 7.5, for 15, 23, 31 and 40 dop, respectively. B. napus Surpass 402 showed high susceptibility on cotyledons of 15 dop but moderate resistance on leaves of other ages, with DI% values of 59.0, 31.2, 27.1 and 26.2 for 15, 23, 31 and 40 dop, respectively. B. napus Hyola 450 TT showed very high susceptibility at the cotyledon stage on 15 dop, but some resistance on 23 dop and more so on 31 and 40 dop, with DI% values of 84.0, 41.2, 35.4 and 32.9 for 15, 23, 31 and 40 dop, respectively. Together, these findings explain for the first time why development of downy mildew epidemics on susceptible cultivars occurs early in the growing season when warmer seasonal temperatures in autumn coincide with presence of seedlings; in contrast to later in the growing season on less susceptible older plants coinciding with cooler and less favourable winter temperatures. Increasing maximum and minimum temperatures associated with climate change have likely fostered the increased severity of downy mildew over the past 15 years.  相似文献   

6.
Phytophthora capsici infection of chili pepper seedlings can cause substantial losses due to damping-off and collar rot diseases. Chemical control is no longer effective due to reported resistance development, on top of the related environmental concerns and the consumer demands for reduced use of fungicides. Biological control is a sustainable option, with several agents having been reported to be effective against this pathogen. This research focused on optimizing the application of strain THSW13 of Trichoderma hamatum and a bacterial isolate BJ10–86 with the objectives of improving chili pepper seed germination, reduce damping-off disease incidence, and improve the growth of the seedlings. Bacterial isolate BJ10–86 was subjected to molecular identification and found to be Pseudomonas aeruginosa. Chili pepper seeds treated with the biocontrol agents, individually or in combination, were seeded into commercial nursery media that had been pre-inoculated with P. capsici zoospores. Over a period of 35 days the chili pepper seed treatments significantly (P = 0.008) reduced the disease incidence of seedlings damping-off. Combined application of T. hamatum and P. aeruginosa was the best biocontrol treatment with an area under disease curve of only 36.61 units compared to 92.87 units for the control treatment. Similar results were observed in vitro where T. hamatum and P. aeruginosa synergistically inhibited P. capsici growth by 73.2 %. The inhibition activity of this treatment was similar to mefenoxam treatment, which implies that it is an effective and sustainable alternative for chili pepper seed treatment. The biocontrol seed treatment had no effect on seed germination and seedling growth.  相似文献   

7.
Four Bt cotton hybrids, each with one of four different events, viz., MRC 6301 Bt (cry1Ac gene), JKCH 1947 Bt (modified cry1Ac gene), NCEH 6R Bt (fusion cry1Ac/cry1Ab gene) and MRC 7017 Bollgard II (cry1Ac and cry2Ab genes) were compared for survival and development of Earias vittella (Fabricius) along with their isogenic non-Bt genotypes. None of the neonates were able to complete the larval period and reach pupal stage on squares of 90, 120 and 150 days old crop of all Bt hybrids. Likewise, on bolls also, zero per cent larval survival was observed in all Bt hybrids except JKCH 1947 Bt where 0.67 per cent larvae could manage to reach pre-pupal stage at 120 and 150 days old crop but failed to form cocoon and enter pupal stage. The surviving larva took more development time (3.7 to 5.4 days) as compared to larvae fed on bolls of JKCH 1947 non-Bt. The average survival period (ASP) of larvae was in order of 150 > 120 > 90 days old crop among the crop ages; JKCH 1947 Bt > MRC 6301 Bt > NCEH 6 R Bt > MRC 7017 Bollgard II among Bt hybrids; and bolls > squares between fruiting bodies. However, reverse was true for speed index of toxic effect. The concentration of Cry toxin varied significantly in squares and bolls and also among the crop ages. The amount of Cry toxin in squares and bolls had significant negative correlation with ASP of the E. vittella larvae.  相似文献   

8.
Interaction between the phytonematode Meloidogyne enterolobii and the fungus Fusarium solani has caused direct and indirect losses in the entire guava production chain and consequent extermination of guava plantations throughout Brazil. The combined action of these two pathogens is known as “guava decline”. In order to obtain and assess Psidium spp. interspecific hybrids for resistance to the nematode M. enterolobii, interspecific crosses of P. guineense (susceptible araçá) x P. cattleyanum (resistant araçá); P.guineense (susceptible araçá) x P. guajava (susceptible guava) and P. cattleyanum (resistant araçá) x P. guajava (susceptible guava) were conducted. These crosses resulted in hybrid immune, susceptible and resistant to Meloidogyne enterolobii. The chi-square test rejected the hypothesis of monogenic inheritance with incomplete dominance, which corroborates that this trait has polygenic action. Predictions of genetic values ??and parameters were obtained by the REML / BLUP procedure, at individual level. Finally, the 30 selected individuals (immune and resistant) were obtained, which will be backcrossed with guava for the recovery of the agronomic traits desired and subsequent release of a new cultivar.  相似文献   

9.
Tomato (Solanum lycopersicum L.) ARGINASE2 (ARG2) and THREONINE DEAMINASE2 (TD2) are involved in plant defense. These enzymes act in the midgut of herbivores fed on tomato plants to degrade the essential amino acids Arg and Thr, respectively. Although it has been demonstrated that overexpression of the SlARG2 gene in tomato enhanced its resistance against M. sexta larvae, knock-down the expression of SlTD2 reduced the resistance of tomato to lepidopteran herbivores; it remains unclear whether overexpression of SlTD2 could enhance the resistance of the host plants to herbivores, or whether combined overexpression of SlARG2 and SlTD2 could lead to synergistically enhanced resistance to insects. Here, we generated transgenic Arabidopsis plants overexpressing SlARG2 (SlARG2 OE) and SlTD2 (SlTD2 OE) individually as well as in combination (SlARG2-SlTD2 OE). Overexpression of these genes did not affect Arabidopsis development, seed yield, or Arg and Thr content. Insect-feeding bioassay was performed by feeding diamondback moth (Plutella xylostella L.) larvae on detached leaves of wild-type, SlARG2 OE, SlTD2 OE, and SlARG2-SlTD2 OE plants. Larvae fed on SlARG2 OE leaves showed approximately 31% to 35% reduction in weight and 6% to 10% reduction in survival rate compared to those fed on wild-type leaves. Although larvae fed on SlTD2 OE leaves showed no reduction in survival rate, they gained less weight. Whereas larvae fed on SlARG2-SlTD2 OE leaves showed neither reduction in weight nor reduction in survival rate. We further investigated the arginase enzymatic activity of the SlARG2 OE and SlARG2-SlTD2 OE transgenic plants. The SlARG2 OE line most resistant to diamondback moth larvae displayed the highest arginase activity. Our data indicate that overexpression of SlARG2 or SlTD2 in Arabidopsis can enhance its resistance against diamondback moth, whereas combined overexpression of SlARG2 and SlTD2 did not generate synergistically increased resistance to diamondback moth.  相似文献   

10.
Ability to detect Pseudocercospora macadamiae infection in macadamia husk at least four months before symptoms become visible will aid the development of disease control measures. This study examined the distinctness of P. macadamiae within the phylogenetic lineages of the genus Pseudocercospora. In addition, we developed two quantitative PCR (qPCR) assays, as rapid diagnostic tools, for early detection and quantification of P. macadamiae in planta. Phylogenetic analysis of concatenated sequences of four gene loci (large subunits, internal transcribed spacer (ITS), translation elongation factor 1-alpha (TEF-1α) and actin of 47 P. macadamiae isolates showed that P. macadamiae is a distinct species in the genus Pseudocercospora. P. macadamiae isolates were partitioned into subunits in the cluster but the grouping of the isolates was regardless of location. Nucleotide diversity (0.02) and the coefficient of genetic differentiation (0.07) were low in the P. macadamiae population. Two qPCR primer sets, based on ITS (PMI) and TEF-1α (PME) were designed that consistently amplified P. macadamiae in fungal cultures (Ct = 16.93 ± 0.11 and Ct = 21.20 ± 0.11, respectively) and in planta (Ct = 32.36 ± 0.28 and Ct = 38.07 ± 1.20, respectively). The PMI primers also detected species in the genus Pseudocercospora, while PME was more specific and robust for quantification of P. macadamiae. Both primer sets detected P. macadamiae in asymptomatic tissue samples and strongly differentiated various stages of disease progression, which revealed approximately 10-fold increase in fungal biomass between each consecutive stage of symptom development.  相似文献   

11.
The vector competence of Frankliniella occidentalis for Chrysanthemum stem necrosis virus (CSNV) was evaluated. Three vector strains with distinct competences for Tomato spotted wilt virus (TSWV) transmission were investigated, including an artificially selected strain (TsH) that has a particularly high competence (>90 %). Newly hatched larvae of F. occidentalis were given an acquisition access period of 5 days on CSNV-infected D. stramonium leaves, and reared to maturity. Their transmission efficiencies were examined using a leaf disk assay using Petunia x hybrida leaves. Following the leaf disk assay, the virus accumulation in the vectors was examined via a double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) of their bodies. The results showed that the CSNV acquisition and transmission efficiency of the TsH strain did not differ from those of the others, indicating that the competence of F. occidentalis as a vector for CSNV is not related to that for TSWV. The CSNV transmission and acquisition efficiencies of two F. intonsa strains (Hiroshima and Fukuoka) were also evaluated. In Hiroshima strain, 35 % of adults were viruliferous, but only two transmitters (3 %) were observed. In Fukuoka strain, 6 % were viruliferous, and no transmitters were observed. These results indicate that F. intonsa cannot be a major vector for CSNV. The accumulation of CSNV in the adults of F. occidentalis and F. intonsa evaluated using DAS-ELISA showed a significant difference in ELISA values among transmitter, viruliferous non-transmitter, and non-viruliferous individuals. These results clearly demonstrated that only transmitters that accumulated a threshold quantity of virus can transmit CSNV to plants.  相似文献   

12.
Fifteen okra germplasm entries viz. accessions: IC0506027, IC0506118 and EC0306728; Abelmoschus spp.: Abelmoschus tuberculatus, Abelmoschus moschatus, Abelmoschus angulosus, Abelmoschus tetraphyllus, Abelmoschus manihot and Abelmoschus caillei; genotypes: POL-6 and POL-7; and four cultivated varieties: Punjab 8, Punjab Padmini, Punjab 7 and Pusa Sawani were screened against jassid, Amrasca biguttula biguttula (Ishida) in field at Vegetable Research Farm, Department of Vegetable Science, Punjab Agricultural University, Ludhiana, India during Kharif 2015. Different morphological and biochemical parameters of leaves of the selected entries were also studied. The correlation between jassid nymphal population and mid vein hair density, total phenols and tannins was negative and significant (r = ?0.67, ?0.83, ?0.75, respectively); negative and non-significant for hair length, angle of insertion of hair, total sugars and silica (r = ?0.40, ?0.49, ?0.63 and ?0.59, respectively) and positive and highly significant for lacination index, reducing sugars and lignins (r = 0.82, 0.95 and 0.90, respectively). Abelmoschus spp. Abelmoschus tetraphyllus, Abelmoschus angulosus and Abelmoschus moschatus were found to be field resistant on the basis of significantly lower pooled jassid nymphal population (1.56–1.99), jassid injury index (1.16–1.27) and susceptibility index (2.70–2.92). High degree of resistance in Abelmoschus tetraphyllus, Abelmoschus angulosus and Abelmoschus moschatus was found to be associated with high hair density (4.75–7.50), longer hair (1285.00–1513.20 μm), more erect hair (83.40–95.20°), broad leaves, high total sugars (15.21–18.36 mg/g), total phenols (1.52–1.58 mg/g), tannins (26.12–31.48 mg/g) and silica (32.66–33.17 mg/g) and low levels of reducing sugars (2.50–3.39 mg/g). Abelmoschus tuberculatus, A. manihot, IC0506027 and EC0306728 were found moderately field resistant with variable levels of morphological and biochemical parameters. High hair density, broad leaves, moderate levels of total sugars, reducing sugars, total phenols, tannins and silica seems to be associated with moderate levels of resistance in these entries. The variable levels of above mentioned parameters in moderately resistant entries also indicate that a single factor is not responsible for resistance but combination of different factors may be conferring resistance to jassid.  相似文献   

13.
The cotton stainer, Dysdercus koenigii Fabricius (Hemiptera: Pyrrhcoridae), has become a major threat to transgenic cotton as it causes warts on the internal carpel wall of cotton boll, severe lint staining, lint locks, and lint lesions. Thus, keeping in view the importance of this pest on cotton, in the present study, screening of 13 transgenic cotton genotypes was performed and the population of D. koenigii was determined on these genotypes during 2012–13. Furthermore, among these genotypes, a high yielding advanced cultivar (FH-114) was selected for further experiments. A number of five different densities of D. koenigii (5, 10, 15, 20, and 25) at adult stage with well-developed proboscis were released in the cages along with a control treatment. Cotton genotypes FH-312, FH-2073, FH-Lalazar, FH-142, and MNH-886 possessed minimum population (1.33 D. koenigii per plant) compared to FH-324 and FH-444 (6.0 D. koenigii per plant). The number of bolls per plant and boll weight decreased as a result of increased densities. The increased density of D. koenigii resulted in fewer bolls per plant (12.1 bolls), reduced boll weight (2.1 g), germination (39.1%), ginning out turn (38.3%), staple length (27.8 mm), and staple fineness (4.0 μg/in.) when compared with un-infested plants (30.6, 3.2 g, 77.3%, 41.5%, 28.8 mm, and 4.4 μg/in.), respectively. Correlation analysis revealed that bolls per plant, boll weight, germination, ginning out turn, and staple fineness resulted in negative and significant correlation with density of D. koenigii with r-values of ?0.95, ?0.98, ?0.98, ?0.8, and ?0.85, respectively. Coefficient of determination (R2) demonstrated that bolls per plant, boll weight, germination, ginning out turn, staple length, and staple fineness contributed with 91, 96, 96, 79, 43 and 73%, respectively, to the total variability at different densities of D. koenigii. Our findings demonstrated that D. koenigii has become potential major pest and causes quantitative and qualitative losses to transgenic cotton, hence, there is a need to develop appropriate control measures for controlling its population to avoid further losses.  相似文献   

14.
We evaluated the chemical composition of thirteen commercially available plant essential oils and their insecticidal activity against the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae). Gas chromatography-mass spectrometry was used to characterize the chemical components of the essential oils. A total of 113 compounds were identified, with terpenes (>80%) and aromatic compounds as primary constituents. The toxicity of each pure essential oil was tested separately on third instar larvae and adult beet armyworms by topical application of 0.5 μl oil/ insect. All plant essential oils were found to be harmful to S. exigua, with third instar larvae showing significantly more susceptibility than adults. Essential oils of Cinnamomum zeylanicum and Juniperus virginiana showed the highest toxicity (mortality above 90%) to larvae, while C. zeylanicum and Pogostemon cablin oils were the most harmful compounds (95% mortality) to adults. Cymbopogon winterianus oil caused delayed mortality (similar to the effects of insect growth regulators) as well as malformations in pupae. C. winterianus, Ocimum basilicum and Rosmarinus officinalis oils significantly reduced fecundity, whereas no significant effects were observed on fertility.  相似文献   

15.
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16.
Zonate leaf spot (Gloeocercospora sorghi) is a common disease in Sorghum bicolor producing areas of the U.S., but little is known about its biology, virulence and severity on S. bicolor, Zea mays, and related crop grassweeds. Greenhouse studies were conducted to determine and compare the virulence and severity of G. sorghi on 10 commercially available sorghum hybrids, four Z. mays hybrids and selected grassweed species including Sorghum bicolor (grain sorghum and shattercane biotypes) and Sorghum halepense (Johnsongrass), two of the most problematic arable weeds. Plants from the respective species were inoculated with a local G. sorghi isolate and maintained in a dew-chamber at 24 °C for 24 h and then incubated under greenhouse conditions for 4 weeks. Plants were observed for lesion expression and rated using a modified Horsfall-Barrett scale (0–10). The first symptoms of infection were visible within 24 h following inoculation on shattercane and S. bicolor hybrids. Symptoms consisted of small, non-diagnostic purple lesions on the leaves. Results showed that S. bicolor, S. halepense and shattercane were susceptible to G. sorghi. All other species tested in this study were not infected. More particularly, disease severity, increased from a rating of 3 to 10 on sorghum and from 2 to 7 on S. halepense between 2 and 23 days after inoculation, respectively. However, disease severity on shattercane increased rapidly from 3.5 to 10 between 2 and 8 days after inoculation, respectively. Among the sorghum hybrids tested, FFR-322 appeared to be the most resistant to G. sorghi while Pioneer 83G66 appeared to be the most susceptible. Z. mays hybrids were not infected by the fungus used in this study. G. sorghi could be used effectively to manage shattercane and S. halepense infestations occurring in Z. mays and S. bicolor fields consisting of specific G. sorghi-resistant hybrids.  相似文献   

17.
Biosynthesis of the oxylipin jasmonic acid (JA) in Arabidopsis thaliana is catalyzed by a single allene oxide synthase (AOS)-encoding gene and four genes encoding four functional allene oxide cyclase (AOC) polypeptides (AOC1, AOC2, AOC3, and AOC4). To elucidate the biological activities of the JA pathway in regulating the plant defense response to plant-parasitic nematodes, transgenic lines carrying the GUS reporter gene under the control of individual AOC or AOS promoters were examined. Upon penetration by second-stage juveniles (J2 s), promoter activities of AOC1, AOC3 and AOC4 appeared in the root tip and root-elongation zone, with AOC3 demonstrating highest induction. At 5 days AOC3 activity continued to be highly pronounced in the stele and root cortex, associated with nematode invasion throughout gall initiation and maturation. AOS expression appeared 3 days postinfection and accompanied all later infection stages. Mutant lines were analyzed: disruption in AOS rendered plants more resistant to nematode infection, as reflected by the decreased number of females produced on this line; loss-of-function of AOC3 rendered plants more susceptible to nematode infection. Oxylipins derived from the 9- and 13-lipoxygenase pathways were assayed for their direct inhibitory activity toward M. javanica J2 s. Clear nematicidal activity of the bioactive 9- and 13-hydroperoxides was observed. Oxylipins produced by divinyl ether synthase, colneleic acid, colnelenic acid and ω5(Z)-etherolenic acid demonstrated strong inhibitory activity. These data, along with those of other assayed oxylipins, suggest that temporal and spatial fine tuning of the JA route allowing nematodes parasitism on plant host.  相似文献   

18.
Real-Time PCR assay was used to quantify the expression of marker genes of the salicylic acid, jasmonic acid and ethylene signaling pathways in seven Solanum lines after inoculation with a Ralstonia solanacearum phylotype I strain, R008. Four Solanum lycopersicum lines (CRA 66, Hawaii 7996, MST 32/1, Quatre carrées), one S. tuberosum line (Spunta), the wild Lycopersicon cerasiforme and Solanum commersonii were used for this investigation. Results revealed very little activation of the jasmonic acid pathway marker genes, lipoxygenase A (LoxA) and protease inhibitor II (Pin2), with no significant difference (p > 0.05) in fold change expression among the Solanum lines. In contrast the salicylic acid pathway marker genes, glucanase A (GluA) and PR-1a, and the ethylene pathway marker genes, osmotin-like (Osm) and PR-1b, were expressed at higher levels with a statistically significant difference (p < 0.05) in fold change expression among the Solanum lines. The resistant lines L. cerasiforme, CRA 66, Hawaii 7996 and S. commersonii showed stronger activation of the salicylic acid and ethylene marker genes than the moderately resistant cultivar (MST 32/1) and the susceptible lines (Quatre carrées and Spunta). The marker genes reached their highest expression levels earlier (4 h.p.i) in the resistant and moderately resistant lines than in the susceptible lines (48 h.p.i.). These results indicate that salicylic acid and ethylene signaling pathways have a significant role in defense against R. solanacearum. The timing and magnitude of the upregulation of gene expression may determine the plant ability to put up a defense response against the pathogen.  相似文献   

19.
The purpose of this study was to determine if exogenous cholesterol availability influenced Pythiaceae resistance to antibiosis. Characterisation of an isolate of Phytophthora erythroseptica and Pythium ultimum for tolerance to antibacterial compounds found that 0.05 g.l?1 chloramphenicol inhibited mycelial growth by 96.6 % and 23.5 % respectively. However, the addition of cholesterol (0.01 g l?1) to potato dextrose agar (PDA) containing 0.05 g l?1 chloramphenicol was found to increase mycelial growth of P. erythroseptica, indicating a role for cholesterol in tolerance to inhibitory antibacterial compounds. To determine if this property extended to suppressive effects of a potential biocontrol agent, P. erythroseptica and P. ultimum were then tested against a cell-free filtrate of diffusible metabolites produced by a suppressive Trichoderma harzianum isolate in the presence and absence of cholesterol in PDA. In the absence of cholesterol, diffusible metabolites of the T. harzianum isolate were found to inhibit mycelial growth of P. erythroseptica and P. ultimum on PDA by 98 % and 63.6 % respectively (P?<?0.0001). However, the inhibitory effect of the metabolites was mitigated when 0.005 g l?1 of cholesterol was present in PDA, with mycelial growth of P. ultimum and P. erythroseptica reduced by only 60.4 % and 41.8 %, respectively (P?<?0.0001), much less inhibition than was observed in the absence of cholesterol. These results demonstrated that access to exogenous cholesterol can influence the sensitivity of Pythiaceae species to antibiosis by positively influencing mycelial growth.  相似文献   

20.
Laboratory and nursery experiments were conducted to identify the causal agent of a needle blight of Pinus wallichiana, a species native to the Western Himalayas. The pathogen was identified as Myrothecium verrucaria, on the basis of morphological, cultural and molecular characterization. BLAST analysis of ITS sequences of the pathogen revealed maximum sequence identity of 99% with M. verrucaria. The sequence is the first of this fungus from P. wallichiana. Phylogenetic analysis grouped all M. verrucaria isolates in a single clade; M. roridum and M. inundatum clustered in separate clades. The pathogen grew optimally at 25 ± 1 °C on oat meal agar, pH 5.5. Inoculation experiments with M. verrucaria demonstrated pathogenicity on Pinus halepensis, Cedrus deodara and Cryptomeria japonica, in addition to Pinus wallichiana.  相似文献   

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