Sgabd-2 plays specific role in immune response against biopesticide Metarhizium anisopliae in Aphis citricola.

Metarhizium anisopliae is an effective biopesticide for controlling Aphis citricola, which has developed resistance to many chemical pesticides. However, the powerful immune system of A. citricola has limited the insecticidal efficacy of M. anisopliae. The co-evolution between insects and entomogenous fungi has led to emergence of new antifungal immune genes, which remain incompletely understood. In this study, an important immune gene Sgabd-2 was identified from A. citricola through transcriptome analysis. Sgabd-2 gene showed high expression in the 4th instar nymph and adult stages, and was mainly distributed in the abdominal region of A. citricola. The recombinant protein (rSgabd-2) exhibited no antifungal activity but demonstrated clear agglutination activity towards the conidia of M. anisopliae. RNA interference of Sgabd-2 by dsRNA feeding resulted in decreased phenoloxidase (PO) activity and weakened defense for A. citricola against M. anisopliae. Simultaneous silence of GNBP-1 and Sgabd-2 effectively reduced the immunity of A. citricola against M. anisopliae more than the individual RNAi of GNBP-1 or Sgabd-2. Furthermore, a genetically engineered M. anisopliae expressing double-stranded RNA (dsSgabd-2) targeting Sgabd-2 in A. citricola successfully suppressed the expression of Sgabd-2 and demonstrated increased virulence against A. citricola. Our findings elucidated Sgabd-2 as a critical new antifungal immune gene and proposed a genetic engineering strategy to enhance the insecticidal virulence of entomogenous fungi through RNAi-mediated inhibition of pest immune genes.

Quantitative Analysis of the Migration and Accumulation of Bacillus subtilis in Asparagus officinalis.

Bacillus subtilis B96-II is a broad-spectrum biological control strain. It effectively suppresses soil-borne fungal diseases in vegetables. A green fluorescence protein (GFP) was expressed in B96-II to detect migration of B96-II into the root and stem of asparagus. The GFP-tagged B96-II (B96-II-GFP) strain exhibited bright green fluorescence under a fluorescence microscope. GFP was stable and had no apparent effects on the growth of the strain. Asparagus plants were planted in the soil inoculated with B96-II-GFP. Our results showed that B96-II-GFP was detected in both the root and stem 15, 30, and 45 days after the asparagus seedlings were planted. B96-II-GFP was also detected in leaves but at a lower concentration. The highest concentration was detected in 15 days, and the number of bacteria decreased subsequently irrespective of duration of growth or sampling period. The highest concentration of B96-II-GFP was present in the root base suggesting that the root base served as the hub of bacterial migration from the soil to the stem.

Effects of Genetic Background and Altitude on Sugars, Malic Acid and Ascorbic Acid in Fruits of Wild and Cultivated Apples (Malus sp.).

Soluble sugars, malic acid, and ascorbic acid in 17 apple cultivars (Malus domestica Borkh.) and three wild forms (M. pumila 'Saiwaihong', M. prunifolia (Willd.) Borkh. and M. micromalus Makino) from three major apple cultivation regions in China were quantified using gas chromatography equipped with flame ionization detector (GC-FID). Fructose was the most abundant sugar, followed by sucrose, glucose, and sorbitol. Wild apples contain more sorbitol and less sucrose and were significantly more acidic than cultivated fruits. The total sugar content varied from 110 to 160 mg/g fresh fruits, total acid content from 2 to 6 mg/g, with a strong influence of genetic background and growth location. Overall, 'Gala', 'Xiali', 'Liuyuehong', 'Lihong', 'Starking Delicious', and 'Starkrimson' were characterized by higher sugar/acid ratio indicating sweeter taste compared to other cultivars. The wild apples had the highest content of ascorbic acid (0.6-0.96 mg/g). Compared to other cultivars, 'Zhongqiuwang', 'Qinguan', and 'Nagafu No. 2' were richer in ascorbic acid. The ascorbic acid content in the commercial cultivars was highly dependent on growth location. The content of malic acid and sucrose positively correlated to altitude, and that of glucose negatively. Malic acid positively correlated with ascorbic acid and sucrose, glucose content with ascorbic acid.

[Determination of 4 dithiocarbamate residues in 22 matrices by gas chromatography].

A gas chromatographic method with flame photometric detection (FPD (sulfur filter)) for analyzing the residues of 4 dithiocarbamates in 22 matrices in a heated closed vial has been established. The dithiocarbamate residues were decomposed to carbon disulfide (CS2) by SnCl2-HCl solution. The liberated CS2 was absorbed by hexane in the vial, and then determined by gas chromatography with FPD (sulfur filter). The results were expressed as the residues of dithiocabamates. The residue analysis method was validated by mancozeb, metiram, propineb and thiram in 22 matrices (apple, grape, etc). The average recovery ranges were from 72% to 110% with the relative standard deviations (RSD) between 0.8% and 22.0% when the fortified concentrations were between 0.06 and 3.0 mg/kg, and the quantitative analysis was performed by using external standard method. The limits of detection were in the range of 0.01-0.1 mg/kg (S/N = 3), and the limits of quantification were between 0.02 and 0.2 mg/kg (S/N = 10) for the 4 dithiocarbamate residues in the 22 matrices. This method is simple, fast, accurate, reproducible, and suitable for the determination of the 4 dithiocarbamate residues in the matrices mentioned in this paper.

[Effects of sub-lethal dosages abamectin on food intake and digestive enzyme activities of silkworm Bombyx mori L].

Mulberry leaves treated with sub-lethal dosages (LC5, LC10 and LC20) abameetin were fed to the 5th instar larvae of silkworm (Bombyx mori L.), and the food intake and digestive enzyme activities of the larvae were studied by using gravimetric method and measuring enzyme activities. The results showed that sub-lethal dosages abameetin significantly inhibited the growth and food intake of the larvae, with their body mass and its increase rate as well as their relative growth rate being significantly lower than the control, and accompanied with the decreases of food intake, its relative consumption rate, and feces amount. The efficiency of the conversion of ingested food (ECI) and that of the conversion of digested food (EDI) also reduced, but the approximate digestibility (AD) increased significantly. The amylase and sucrase activities in the midgut of the larvae treated with abameetin decreased significantly for a longer time at the beginning, and then recovered to the same as or a higher level than the control, whereas the trehalase activity decreased significantly for a shorter time at the beginning, then increased significantly, and finally recovered to the normal. It was suggested that sub-lethal dosages abameetin had definite toxicity to the silkworm, and the toxic effect was increased with increasing dosage, which could result in the turbulence of silkworm's digestive system, and further, affect its food intake and its growth and development.

[Biodegradation of acetochlor in soil and its persistence against Echinochloa crusgalli].

Gas chromatograph and bioassay were used to study biodegradation of acetochlor and its influence on the persistence against Echinochloa crusgalli in soil. The results showed that half-life of degradation of acetochlor was significantly shorter in unsterilized soil than that in sterilized soil under the same experimental conditions of concentrations, water content and temperature, when acetochlor was added to the soil with concentrations of 1.25, 2.5 and 5.0 mg x kg(-1) respectively, which demonstrated that microorganisms could evidently degrade acetochlor in soil. The experiment on degradation of three main kinds of microorganism cultivated in liquid culture medium gave same results above. The bioassay' s result showed that the period of acetochlor persistence against Echinochloa crusgalli was shorter in unsterilized soil than that in sterilized soil, which indicated that existence of microorganism could accelerate the degradation of acetochlor and shorten remaining time of the herbicide in soil, consequently reduce its persistence against the weed.