Rapid and Quantitative Detection of Leifsonia xyli subsp. xyli in Sugarcane Stalk Juice Using a Real-Time Fluorescent (TaqMan) PCR Assay

Larvicidal, antioxidant and biotoxicity assessment of (2-(((2-ethyl-2 methylhexyl)oxy)carbonyl)benzoic acid isolated from Bacillus pumilus against Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus

Mosquitoes are a vector for many dreadful diseases known for their public health concern. The continued use of synthetic insecticides against vector control has led to serious environmental impacts, human health problems, and the development of insect resistance. Hence, alternative mosquito control methods are needed to protect the environment and human health. In the present study, the bioefficacy of (2-(((2-ethyl-2 methylhexyl)oxy)carbonyl) benzoic acid isolated from Bacillus pumilus were tested against Aedes aegypti, Culex quinquefasciatus and Anopheles stephensi. The isolated bioactive compound was characterized through thin layer chromatography (TLC), UV-visible spectroscopy (UV), Fourier-transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and gas chromatography-mass spectrometry analysis. The pure compound caused a high percent mortality rate in a dose-dependent manner, the obtained values were 96, 82, 69, 50 and 34%; 86, 72, 56, 43, and 44%; 100, 90, 83, 70 and 56% against Ae. aegypti, Cx. quinquefasciatus, and An. stephensi respectively. The effective lethal concentration values (LC₅₀) were 13.65, 14.90 and 9.64 ppm against Ae. aegypti, Cx. quinquefasciatus, An. Stephensi, respectively. The effect of (2-(((2-ethyl-2 methylhexyl)oxy)carbonyl) benzoic acid significantly increased the superoxide dismutase, catalase, α, β esterase and Glutathione-S-transferase level after 24 h of the treatment period. The comet assay confirmed that isolated compound causes DNA damage in all tested insects. Histopathological examinations of treated larvae showed shrunken body posture, damaged epithelial cells and microvillus as compared to control organisms. The biosafety of the isolated compound was assessed against G. affinis and did not produce mortality which confirmed that the activity of the isolated compound is species specific. The current study concludes that the critical success factors of new insecticidal agent development are based on the eco-compatibility and alternative tools for the pesticide producing industry.

Molecular Detection and Quantification of Xanthomonas albilineans in Juice from Symptomless Sugarcane Stalks Using a Real-Time Quantitative PCR Assay

Leaf scald, a bacterial disease caused by Xanthomonas albilineans (Ashby) Dowson, is a major limiting factor for sugarcane production worldwide. Accurate identification and quantification of X. albilineans is a prerequisite for successful management of this disease. A sensitive and robust quantitative PCR (qPCR) assay was developed in this study for detection and quantification of X. albilineans using TaqMan probe and primers targeting a putative adenosine triphosphate-binding cassette (ABC) transporter gene (abc). The novel qPCR assay was highly specific to the 43 tested X. albilineans strains belonging to different pulsed-field gel electrophoresis groups. The detection thresholds were 100 copies/µl of plasmid DNA, 100 fg/µl of bacterial genomic DNA, and 100 CFU/ml of bacterial suspension prepared from pure culture. This qPCR assay was 100 times more sensitive than a conventional PCR assay. The pathogen was detected by qPCR in 75.1% (410/546) of symptomless stalk samples, whereas only 28.4% (155/546) of samples tested positive by conventional PCR. Based on qPCR data, population densities of X. albilineans in symptomless stalks of the same varieties differed between two sugarcane production areas in China, Beihai (Guangxi Province) and Zhanjiang (Guangdong Province), and no significant correlation between these populations was identified. Furthermore, no relationship was found between these populations of the pathogen in asymptomatic stalks and the resistance level of the sugarcane varieties to leaf scald. The newly developed qPCR assay proved to be highly sensitive and reliable for the detection and quantification of X. albilineans in sugarcane stalks.

Targeted Metabolic Profiles of the Leaves and Xylem Sap of Two Sugarcane Genotypes Infected with the Vascular Bacterial Pathogen Leifsonia xyli subsp. xyli

Ratoon stunt (RS) is a worldwide disease that reduces biomass up to 80% and is caused by the xylem-dwelling bacterium Leifsonia xyli subsp. xyli. This study identified discriminant metabolites between a resistant (R) and a susceptible (S) sugarcane variety at the early stages of pathogen colonization (30 and 120 days after inoculation—DAI) by untargeted and targeted metabolomics of leaves and xylem sap using gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS), respectively. Bacterial titers were quantified in sugarcane extracts at 180 DAI through real-time polymerase chain reaction. Bacterial titers were at least four times higher on the S variety than in the R one. Global profiling detected 514 features in the leaves and 68 in the sap, while 119 metabolites were quantified in the leaves and 28 in the sap by targeted metabolomics. Comparisons between mock-inoculated treatments indicated a greater abundance of amino acids in the leaves of the S variety and of phenolics, flavonoids, and salicylic acid in the R one. In the xylem sap, fewer differences were detected among phenolics and flavonoids, but also included higher abundances of the signaling molecule sorbitol and glycerol in R. Metabolic changes in the leaves following pathogen inoculation were detected earlier in R than in S and were mostly related to amino acids in R and to phosphorylated compounds in S. Differentially represented metabolites in the xylem sap included abscisic acid. The data represent a valuable resource of potential biomarkers for metabolite-assisted selection of resistant varieties to RS.

Improved Primers for the Specific Detection of Leifsonia xyli subsp. xyli in Sugarcane Using a Conventional PCR Assay

Ratoon stunting disease (RSD), one of the most important diseases of sugarcane, is caused by the bacterium Leifsonia xyli subsp. xyli (Lxx). Lxx infects sugarcane worldwide and RSD results in high yield losses and varietal degeneration. It is highly challenging to diagnose RSD based on visual symptomatology because this disease does not exhibit distinct external and internal symptoms. In this study, a novel Lxx-specific primer pair Lxx-F1/Lxx-R1 was designed to detect this pathogen using a conventional PCR assay. These primers were then compared with four published Lxx-specific primers and one universal Leifsonia generic primer pair LayF/LayR. Sugarcane leaf samples were collected from Saccharum spp. hybrids in commercial fields (315 samples) and from germplasm clones of five Saccharum species and Erianthus arundinaceus (216 samples). These samples were used for comparative field diagnosis with six conventional PCR assays. Sensitivity tests suggested that the PCR assay with primers Lxx-F1/Lxx-R1 had the same detection limit (1 pg of Lxx genomic DNA) as the primer pairs Cxx1/Cxx2 and CxxITSf#5/CxxITSr#5 and had 10-fold higher sensitivity than the primer pairs Pat1-F2/Pat1-R2, LayF/LayR, and C2F/C2R. Comparison of PCR assays revealed that natural Lxx-infection incidence (6.1%) in field sample evaluation identified by Lxx-F1/Lxx-R1 primers was higher than incidences (0.7 to 3.0%) determined by other primer pairs. Moreover, no nonspecific DNA amplification occurred within these field samples with Lxx-F1/Lxx-R1 primers, unlike with the primer pairs Cxx1/Cxx2 and LayF/LayR. Diverse Leifsonia strains were identified by PCR detection with LayF/LayR primers in the field samples, whereas whether these Leifsonia strains were pathogenic to sugarcane requires further research. Our investigations revealed that the PCR assay with the newly designed primers Lxx-F1/Lxx-R1 could be widely used for RSD diagnosis and Lxx-pathogen detection with satisfactory sensitivity and specificity.