Organic mulch can suppress litchi downy blight through modification of soil microbial community structure and functional potentials.

BACKGROUND: Organic mulch is an important management practice in agricultural production to improve soil quality, control crop pests and diseases and increase the biodiversity of soil microecosystem. However, the information about soil microbial diversity and composition in litchi plantation response to organic mulch and its attribution to litchi downy blight severity was limited. This study aimed to investigate the effect of organic mulch on litchi downy blight, and evaluate the biodiversity and antimicrobial potential of soil microbial community of litchi plantation soils under organic mulch. RESULTS: Organic mulch could significantly suppress the disease incidence in the litchi plantation, and with a reduction of 37.74% to 85.66%. As a result of high-throughput 16S rRNA and ITS rDNA gene illumine sequencing, significantly higher bacterial and fungal community diversity indexes were found in organic mulch soils, the relative abundance of norank f norank o Vicinamibacterales, norank f Vicinamibacteraceae, norank f Xanthobacteraceae, Unclassified c sordariomycetes, Aspergillus and Thermomyces were significant more than that in control soils. Isolation and analysis of antagonistic microorganism showed that 29 antagonistic bacteria strains and 37 antagonistic fungi strains were unique for mulching soils. CONCLUSIONS: Thus, we believe that organic mulch has a positive regulatory effect on the litchi downy blight and the soil microbial communities, and so, is more suitable for litchi plantation.

First report of powdery mildew of crape jasmine (Tabernaemontana divaricata) caused by Erysiphe elevata in China.

Crape jasmine (Tabernaemontana divaricata) is a popular flowering shrub widely grown in southern China. Its leaves and roots are used in Chinese traditional medicine. In December, 2019, powdery mildew symptoms were observed on five crape jasmine shrubs on the campus of Shenzhen Polytechnic (22°35'N; 113°56'E), in Guangdong province. Approximately 45% of leaves were infected. Symptoms initially appeared as circular to irregular white patches on the leaf petiole, and subsequently coalesced to develop into abundant hyphal growth on both sides of the leaves, which soon wilted. Hyphae were septate, branched, with simple kidney-shaped to moderately lobed appressoria. Conidia formed singly, ellipsoid-ovoid to subcylindrical, 27-37 × 14-20 µm (mean 32±2.5 × 17±1.6 µm), with a length/width ratio varying from 1.3 to 2.4. Conidiophores were erect, unbranched, consisted of two cells, 60 to 84 µm long (mean 73±4 µm), and with straight to severely kinked cylindrical foot-cells at the base, 29-35 × 3-7 µm (mean 32±3 × 6±2 µm). Chasmothecia were not observed on sampled plants. These morphological characteristics were typical to the conidial stage of the genus Erysiphe (Braun and Cook, 2012). For molecular identification, genomic DNA was extracted from conidia washed from infected leaves and using Fungal DNA Kit (Omega Bio-tek Inc., Guangzhou, China). Semi-nested PCR amplification of the internal transcribed spacer (ITS) region of rDNA was conducted by using primer sets P3 (Kusaba et al., 1995)/ITS5 and ITS5/ITS4 (White et al., 1990) for the first and second reactions, respectively. BLASTn analysis of the obtained 719 bp sequence (GenBank Accession No. MT802112) showed 99.7% identity with those of E. elevata (KY660910, MH985631, MK253282). On the basis of morphological and molecular analyses, the fungus was identified as Erysiphe elevata. To confirm pathogenicity, infected leaves were gently pressed onto healthy leaves of three healthy plants in separate pots, and three noninoculated plants were used as controls. All plants were maintained in a greenhouse at 25 ℃, and relative humidity of 50 to 65%. After 11 days, similar disease symptoms were observed on the inoculated plants while no symptoms developed on control plants. The fungus observed on the inoculated shrubs was identical morphologically to that o the original infected leaves. E. elevata is a common powdery mildew species infecting Catalpa spp. (Cook et al., 2006), Plumeria rubra (Wu et al., 2019; Yeh et al., 2019) and Eucalyptus camaldulensis (Meeboon and Takamatsu, 2017). However, no powdery mildew were found on P. rubra nearby. To our knowledge, this is the first report of this fungus infecting T. divaricata.

Comparison of different combined treatment processes to address the source water with high concentration of natural organic matter during snowmelt period.

The source water in one forest region of the Northeast China had very high natural organic matter (NOM) concentration and heavy color during snowmelt period. The efficiency of five combined treatment processes was compared to address the high concentration of NOM and the mechanisms were also analyzed. Conventional treatment can hardly remove dissolved organic carbon (DOC) in the source water. KMnO4 pre-oxidization could improve the DOC removal to 22.0%. Post activated carbon adsorption improved the DOC removal of conventional treatment to 28.8%. The non-sufficient NOM removal could be attributed to the dominance of large molecular weight organic matters in raw water, which cannot be adsorbed by the micropore upon activated carbon. O3+activated carbon treatment are another available technology for eliminating the color and UV254 in water. However, its performance of DOC removal was only 36.4%, which could not satisfy the requirement for organic matter. The limited ozone dosage is not sufficient to mineralize the high concentration of NOM. Magnetic ion-exchange resin combined with conventional treatment could remove 96.2% of color, 96.0% of UV254 and 87.1% of DOC, enabling effluents to meet the drinking water quality standard. The high removal efficiency could be explained by the negative charge on the surface of NOM which benefits the static adsorption of NOM on the anion exchange resin. The results indicated that magnetic ion-exchange resin combined with conventional treatment is the best available technology to remove high concentration of NOM.