Common root rot, caused by Bipolaris sorokiniana, is one of the most prevalent diseases of wheat and has led to major declines in wheat yield and quality worldwide. Here, strain XZ34-1 was isolated from soil and identified as Bacillus amyloliquefaciens based on the morphological, physiological, biochemical characteristics and 16S rDNA sequence. Culture filtrate (CF) of strain XZ34-1 showed a high inhibition rate against B.sorokiniana and had a broad antifungal spectrum. It also remarkably inhibited the mycelial growth and spore germination of B. sorokiniana. In pot control experiments, the incidence and disease index of common root rot in wheat seedlings were decreased after treatment with CF, and the biological control efficacy was significant, up to 78.24%. Further studies showed XZ34-1 could produce antifungal bioactive substances and had the potential of promoting plant growth. Lipopeptide genes detection with PCR indicated that strain XZ34-1 may produce lipopeptides. Furthermore, activities of defense-related enzymes were enhanced in wheat seedlings after inoculation with B.sorokiniana and treatment with CF, which showed induced resistance could be produced in wheat to resist pathogens. These results reveal that strain XZ34-1 is a promising candidate for application as a biological control agent against B.sorokiniana.
Rhizoctonia cerealis is a worldwide soil-borne pathogenic fungus that significantly infects wheat and causes sharp eyespot in China. However, the biocontrol strains used for the control of Rhizoctonia cerealis are insufficient. In the present study, antagonistic strain B1302 from the rhizosphere of wheat were isolated and identified as Bacillus mojovensis based on their morphological, physiological, and biochemical characteristics, and their 16S rDNA sequence. Culture filtrate of strain B1302 had a broad antifungal spectrum. In order to improve the antifungal activity of B1302, response surface methodology (RSM) was used to optimize the culture conditions. The final medium composition and culture conditions were 13.2 g/L of wheat bran, 14.1 g/L of soybean meal, 224 r/min of rotation speed, 7.50 of initial pH, and 1.5 × 108 CFU/mL of inoculation amount at 35 °C for a culture duration of 72 h. B. mojavensis B1302 inhibited the hyphae growth of R. cerealis and produced hydrolytic enzymes (protease, chitinase, and glucanase), IAA, and had N-fixing potentiality and P-solubilisation capacity. It can also promote wheat seedling growth in potted plants. The disease incidence and index of wheat seedlings were consistent with the effect of commercial pesticides under treatment with culture filtrate. The biocontrol efficacy of culture filtrate was significant—up to 65.25%. An animal toxicological safety analysis suggested that culture filtrate was safe for use and could be developed into an effective microbial fungicide to control wheat sharp eyespot.
Background Wheat sheath blight, caused by Rhizoctonia cerealis, is a popular fungal disease that causes serious harm to wheat production. Biological control can offer the safe and effective method to control wheat diseases. Results In this study, antagonistic bacteria XZ20-1 and XZ38-3 were isolated and identified as Bacillus amyloliquefaciens and Bacillus velezensis, respectively, and all produced cellulase, protease, amylase and siderophore. To improve antifungal activity, fermentation supernatants of antagonistic bacteria Pseudomonas fluorescens RB5 (previously isolated and stored in the laboratory), B. amyloliquefaciensns XZ20-1 and B. velezensis XZ38-3 were combined and the optimal compound ratio (2:6:4) was quickly screened out through the improved triangle coordinate diagram method. The inhibition rate of compound fermentation supernatants (CFS) reached 61.01%, which was 22.51, 17.05 and 21.42% higher than that of single strain, respectively. The further stability analysis showed that compound fermentation supernatants were relatively stable to pH, temperature, ultraviolet and light. Effect of CFS on pathogen cells through fluorescent microscopy using different stains revealed the mechanism, which CFS can cause cell membrane permeability changed, accumulation of ROS and DNA fragmentation. In the pot experiments, the control efficacy of CFS was 83.05%. Moreover, plant height, root length and fresh weight, chlorophyll and soluble protein of wheat seedlings in CFS treatment groups were more than those in the control group. Conclusions This work screened out the optimal compound ratio of fermentation supernatants by the improved triangular coordinate diagram method firstly and revealed the action mechanism and provides an effective microbial agent for controlling R. cerealis and promoting wheat growth.
To cite this paper: Yang, Y., M. Li and Y. Yi, 2017. The miRNAomes in Rehmannia glutinosa roots exposed to different levels of replanting disease pressure. AbstractRoot development in the medicinal plant Rehmannia glutinosa is severely disordered by replanting disease, which occurs when it is grown in the same soils over consecutive seasons. Following the demonstration of changes to the miRNAome of the R. glutinosa plants in the second year of cultivation, a fuller experiment was organized to track the root miRNAomes over four successive plantings. Four small RNA libraries were generated from the roots of one year's planted (free of replanting disease) and 2-4 years' continuous cultivation (replanting disease) R. glutinosa plants, respectively. Sequencing of these libraries revealed the presence of 18 novel and 344 conserved miRNA families. The abundance of many of the miRNAs varied between the four libraries, consistent with the notion that replanting disease reflects the outcome differential miRNA transcription. A combined bioinformatic and degradome sequencing approach allowed the identification of 69 differentially abundant (DA) miRNA targets, leading to the recognition that particular miRNA/target modules may be important for the expression of the disease. The expression profiles of 28 key miRNAs and their targets implied that the longer years of continuous cultivation was extended, the more severe tendency of these profiles' changes would be. The indication was that the miRNAs-responsive continuous cultivation pressure reprogrammed gene expression patterns, which disordered hormone signaling, repressed core mechanisms, weakened stress tolerance and resulted in forming the disease in R. glutinosa. In conclusion, the key miRNAs involved in important roles of replanting disease and were a crucial basis for exploration in the disease forming repertoire.
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