Volatile compounds from leaves of the African spider plant (Gynandropsis gynandra) with bioactivity against spider mite (Tetranychus urticae)

Previous studies have demonstrated that Gynandropsis gynandra emits acetonitrile as a foliar volatile from intact plants and isolated leaves, and that this compound is an effective spider mite repellent. This study has used gas chromatography–mass spectrometry to investigate volatile compounds emitted from homogenised G. gynandra leaves to evaluate their tissue acetonitrile content and to look for other compounds that might be exploited for the management of spider mites. Acetonitrile was absent from the homogenised tissues of five lines of G. gynandra, studied over two seasons. Thirteen volatile compounds were emitted by G. gynandra at significantly higher levels than mite‐susceptible pot roses, including isothiocyanates, aldehydes, esters, alcohols and terpenes. Six representative compounds were selected to assess bioactivity. Spider mite populations were completely inactive after a 2 h exposure to butyl isothiocyanate, 2,4‐heptadienal or β‐cyclocitral, when evaporated from 0.5 µL of pure compound in a 100 mL air space. The same level of inactivity was achieved after exposure to 5.0 μL of (Z)‐2‐pentenol or a 25 μL volume of 50% v/v Z‐3‐hexenal or 5% w/v methyl isothiocyanate. Dissipation of β‐cyclocitral following 24 h exposure to its concentration of 5 μL in a 100 mL air space resulted in a 6% recovery of the spider mites but at higher concentrations no recovery was observed. These identified compounds may have potential as extracted products for management of spider mites in roses, and a high constitutive content of them in roses may be of value in targeted plant breeding for enhanced insect resistance. The range of isothiocyanates found in G. gynandra accounts for the bitter taste of the leaves when used as a traditional vegetable in Eastern Africa and provides a target for manipulation to improve palatability.     

Variation in leaf structures of micropropagated rhubarb (Rheum rhaponticum L.) PC49

Alterations in leaf trichomes, stomatal characteristics and epidermal cellular features were investigated in micropropagated rhubarb (Rheum rhaponticum L.) PC49. The results showed that micropropagated regenerants had produced significantly lower stomatal index, but larger epidermal cell size than conventional plants. In addition, altered trichome morphology and abnormal stomata, e.g. twin-stomata were constantly noted only in micropropagated plants. The microscopic observation demonstrated a substantially larger intercellular space in palisade and mesophyll only in leaves of micropropagated plants. But the results showed no difference in chloroplast number and chlorophyll content between micropropagated and conventional plants. All the abnormalities suggest somaclonal variation may have occurred in micropropagated rhubarb PC49.     

Cold treatment of Ceratitis capitata (Diptera: Tephritidae) in oranges using a larval endpoint

South Africa currently exports fresh citrus (Citrus spp.) fruit to Japan using an in-transit cold treatment protocol of 14 d or 12 d at temperatures <0 degrees C for treatment of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) in 'Clementine' mandarins (Citrus reticulata Blanco) and other citrus types, respectively. To reduce the risk of chilling injury with this treatment, research was conducted with temperatures >0 degrees C. Earlier South African research had shown that young (6-d-old) larvae were slightly more tolerant of cold treatment and that there were no significant differences between cold tolerance of these larvae in different citrus types [oranges, Citrus sinensis (L.) Osbeck; grapefruits, Citrus paradisi Macfad.; lemons, Citrus limon (L.) Burm.f.; and mandarins). Due to their ready availability, 'Valencia' oranges were used in this study. When 62,492 larvae in total were treated in three replicates at a mean temperature of 1.5 degrees C for 16 d, there were three larval survivors. The trial was therefore repeated with oranges using a 16-d period at a mean temperature of 1.0 degrees C and a mean of 1.4 degrees C for the hourly maximum probe readings. Three replicates were again conducted and the resultant mean mortality in the control was 8.1% of 21,801 larvae, whereas the cold treatment mortality was 100% of 71,756 larvae. This treatment at a mean temperature of 1 degree C exceeded the Japanese confidence level requirement and also exceeded the Probit-9 mortality level, but not at a confidence level of 95%. These data support the establishment of a treatment protocol of 16 d at temperatures <1.4 degrees C, commencing once all fruit pulp probes reach a temperature of 1 degree C or lower.     

False codling moth Thaumatotibia leucotreta (Lepidoptera,Tortricidae) larvae are chill‐susceptible

Abstract This study reports on the low temperature tolerance and cold hardiness of larvae of false codling moth, Thaumatotibia leucotreta. We found that larvae have mean critical thermal minima (lower limits of activity) of 6.7°C which was influenced by feeding status. The effects of low temperature exposure and duration of exposure on larval survival were assessed and showed that the temperature at which 50% of the population survives is ?11.5 ± 0.3°C after 2 h exposure. The supercooling point (SCP, i.e., freezing temperature) was investigated using a range of cooling rates and under different conditions (feeding and hydration status) and using inoculative freezing treatments (in contact with water or orange juice). The SCP decreased significantly from ?15.6°C to ?17.4°C after larvae were fasted for 24 h. Twenty‐four hour treatments at either high or low relative humidity (95.9% or 2.4%) also significantly decreased SCP to ?17.2°C and ?18.2°C respectively. Inoculative freezing (by water contact) raised SCP from ?15.6°C to ?6.8°C which could have important implications for post‐harvest sterilization. Cooling rates did not affect SCP which suggests that there is limited phenotypic plasticity of SCP during the larval life‐stage, at least over the short time‐scales investigated here. In conclusion, larvae of T. leucotreta are chill‐susceptible and die upon freezing. These results are important in understanding this pest's response to temperature variation, understanding pest risk status and improving post‐harvest sterilization efficacy.     

Study of response of Swiss Webster mice to light subunit of mushroom tyrosinase

The light subunit of mushroom, Agaricus bisporus, tyrosinase (LSMT), has been identified as an extrinsic component of the enzyme. Its function is unknown, but it can cross an epithelial cell layer, which suggests that it can be absorbed by the intestine. A similar capability has been demonstrated for the HA-33 component of the progenitor toxin from Clostridium botulinum, which is the closest structural homolog of LSMT. Unlike HA-33, LSMT appears to be non-immunogenic as shown by preliminary tests in Swiss Webster mice. We investigated the immunogenicity and histopathology of LSMT in mice to determine its safety in vivo. LSMT did not evoke generation of antibodies after prolonged periods of intraperitoneal administration. Histopathological observations confirmed the absence of responses in organs after twelve weekly administrations of LSMT. We found that LSMT is not toxic and is less immunogenic than the C. botulinum HA-33 protein, which supports further research and development for pharmaceutical application.     

Transgenic cystic fibrosis mice exhibit reduced early clearance of Pseudomonas aeruginosa from the respiratory tract

The cystic fibrosis (CF) transmembrane conductance regulator (CFTR) has been proposed to be an epithelial cell receptor for Pseudomonas aeruginosa involved in bacterial internalization and clearance from the lung. We evaluated the role of CFTR in clearing P. aeruginosa from the respiratory tract using transgenic CF mice that carried either the DeltaF508 Cftr allele or an allele with a Cftr stop codon (S489X). Intranasal application achieved P. aeruginosa lung infection in inbred C57BL/6 DeltaF508 Cftr mice, whereas DeltaF508 Cftr and S489X Cftr outbred mice required tracheal application of the inoculum to establish lung infection. CF mice showed significantly less ingestion of LPS-smooth P. aeruginosa by lung cells and significantly greater bacterial lung burdens 4.5 h postinfection than C57BL/6 wild-type mice. Microscopy of infected mouse and rhesus monkey tracheas clearly demonstrated ingestion of P. aeruginosa by epithelial cells in wild-type animals, mostly around injured areas of the epithelium. Desquamating cells loaded with P. aeruginosa could also be seen in these tissues. No difference was found between CF and wild-type mice challenged with an LPS-rough mucoid isolate of P. aeruginosa lacking the CFTR ligand. Thus, transgenic CF mice exhibit decreased clearance of P. aeruginosa and increased bacterial burdens in the lung, substantiating a key role for CFTR-mediated bacterial ingestion in lung clearance of P. aeruginosa.     

Comparison of different PCR tests for detecting Shiga toxin-producing Escherichia coli O157 and development of an ELISA-PCR assay for specific identification of the bacteria

In an attempt to develop a standard for ELISA-PCR detection of Shiga toxin producing Escherichia coli (STEC) O157, six published PCR tests were tested in a comparative study on a panel of 277 bacterial strains isolated from foods, animals and humans. These tests were based on the detection of the genes rfbE [J. Clin. Microbiol. 36 (1998) 1801] and rfbB [Appl. Environ. Microbiol. 65 (1999) 2954], the 3' end of the eae gene [Epidemiol. Infect. 112 (1994) 449], the region immediately flanking the 5' end of the eae gene [Int. J. Food. Microbiol. 32 (1996) 103], the flicH7 gene [J. Clin. Microbiol. 35 (1997) 656], or a part of the recently described 2634-bp Small Inserted Locus (SILO(157) locus) of STEC O157 [J. Appl. Microbiol. 93 (2002) 250]. Unlike the other PCR assays, those amplifying the rfb sequences were unable to distinguish toxigenic from nontoxigenic O157. These assays were relatively specific to STEC O157, giving essentially a cross reaction with clonally related E. coli O55 and to a lesser extent with E. coli O145, O125, O126. They also detected the Shiga toxin (stx)-negative derivatives of STEC O157. Based on these results, an ELISA-PCR assay consisting of the solution hybridization of amplicons with two probes that ensured the specificity of the amplification was developed. The ELISA-PCR assay, which used an internal control (IC) of inhibition, was able to detect 1 to 10 copies of STEC O157 in the PCR tube. Adaptation of PCR into ELISA-PCR assay format facilitates specific and sensitive detection of PCR amplification products and constitutes a method of choice for screening STEC O157.     

Dairy Cattle Density and Temporal Patterns of Human Campylobacteriosis and Cryptosporidiosis in New Zealand

EcoHealth - Public health risks associated with the intensification of dairy farming are an emerging concern. Dairy cattle are a reservoir for a number of pathogens that can cause human illness....