Acta Phytopathologica Sinica-Channel: PLANT DISEASE AND CONTROL

The Inhibition of calcium on root rot disease of American ginseng caused by two pathogens

WANG Yi, WANG Yaoyao, ZHANG Mingxin, PENG Na, WANG Xiu, GAO Weiwei — 2024-02-20 00:00:00.0

The root rot caused by Fusarium and Ilyonectria is the most serious disease in American ginseng. The prevention of this disease mainly relies on the utilization of fungicides. However, it is unknown whether it could be controlled by calcium fertilizer. In order to reduce the use of pesticides and find possible physiological and ecological mechanisms of calcium in root rot disease control, a pot experiment was conducted to investigate the effects of calcium application and inoculation. During the cultivation of ginseng, different amounts of calcium oxide (0、0.5、1.5、4.5 g·kg^-1) was applied to the soil. The root biomass, disease incidence, root nutrient content, soil physicochemical properties and soil microbial community were measured. The results showed that low calcium additions increased root rot disease index, however, high calcium additions decreased root rot disease index. Compared to the control, adding 4.5 g·kg^-1 calcium oxide decreased root rot disease index of I. mors-panacis by 87.69% (P < 0.05), meanwhile, the root rot disease index of F. solani was reduced by 66.67% (P>0.05). The calcium content in American ginseng roots from the two inoculation groups were increased by 101.28% and 61.50% (P<0.05), respectively. Nitrogen and phosphorus content in the roots were positively correlated with the root rot disease index of F. solani. On the other hand, the structure and composition of soil microbial communities inoculated with two pathogens differed significantly. The calcium treatment mainly affected the diversity and composition of fungal community, while having little effect on the bacterial commun-ity. Additionally, treatment with 4.5 g·kg^-1calcium oxide inhibited the relative abundance of Didymella and Phoma. Overall, the potential mechanism for the reduction of root rot disease in American ginseng by more than 65% through the application of high-dose calcium is related to increased calcium content in roots, reduced nitrogen and phosphorus content in roots, and decreased the relative abundance of potential pathogens in soil. This study provides a theoretical basis for reducing root rot disease of American ginseng through rational application of calcium fertilizer.

Condition optimization for protoplast preparation of Botrytis cinerea and the pathogenicity of regenerated strains

ZHANG Xiaoyan, XIE Zhao, WANG Xiuhua, LU Baohui, GAO Jie — 2024-02-20 00:00:00.0

In order to obtain high-quality and sufficient protoplasts of Botrytis cinerea that can be used for genetic transformation, effects of multiple parameters including mycelial age, combinations of lytic enzymes, types of osmotic stabilizers, enzymatic hydrolysis temperature, and time of enzyme digestion on protoplasts preparation were studied. The optimal lytic enzyme was determined to be the combination of driselase, snailase, and lysing enzyme at an active ingredient of 1%, 0.1% and 1%, respectively, and the mycelial age, composition and concentration of osmotic stabilizer, enzyme digestion temperature, and enzyme digestion time were as follows: mycelia of JA-6 was cultivated on PDA at 25 °C for 36 h, osmotic stabilizer contained 0.6 mol·L^-1KCl and 50 mmol·L^-1 CaCl₂, and enzyme digestion time was 3 h at 120 r·min^-1 at 28 °C. Enzymatic hydrolysis of 5 g·mL^-1 of B. cinerea mycelium can yield 1.06×10⁷ protoplasts·mL^-1 under above optimal protoplast preparation conditions. No significant differences of the colony morphology, growth rate, conidial production and pathogenicity were observed between the regenerated strain and the wild-type strain. The GFP (green fluorescent protein) gene was subsequently transformed into B. cinerea JA-6 by PEG mediated transformation. The fluorescence signal of the transformants can be stably inherited. The established protoplast preparation method in the present research would meet the requirements of genetic transformation of B. cinerea for further study.

Stress response mechanism of Fusarium graminearum to SDHIs based on transcriptome analysis

2024-02-20 00:00:00.0

In the researches of chemical control of plant diseases, the mechanism of action of fungicides and pathogen resistance to fungicides are the focus of attention, while the mechanisms of how pathogenic bacteria response to mitigate chemical stress is often ignored. The transcriptome sequencing technology was used to study the stress response mechanism of Fusarium graminearum to succinate dehydrogenase inhibitor (SDHIs) fungicides in this study. The results showed that 1 180 up-regulated and 937 down-regulated differentially expressed genes were identified in the pathogen treated with pydiflumetofen and benzovindiflupyr compared to the control. Complex II on mitochondrial electron transfer chain is the target of SDHIs fungicides. Therefore, the genes rela-ted to mitochondrial electron transfer chain were focused in this study. The results showed that F. graminearum responded to the stress of SDHIs fungicides by upregulating the expression of genes such as Succinate dehydrogenase, Ubiquinol-cytochrome C reductase, Fumarylacetoacetate hydrolase (FAH), ABC and MFS transpor-ters, and downregulating the expression of genes in the SWI / SNF complex and other genes. FgFAH gene was induced to express after being treated with SDHIs fungicides. The sensitivity of FgFAH gene-knockout mutant to SDHIs fungicide was increased compared to wild type, indicating that this gene may mediated the stress response of F. graminearum to SDHIs fungicide. The results of this study will provide a research basis for studying stress response mechanism of pathogen to chemical agents and research ideas for developing sensitizers of fungicides in the future.

Impact of whitefly (Bemisia tabaci) on viruliferous rate of sweet potato storage root and viral disease occurrence

2024-02-20 00:00:00.0

Virus disease is a main constraint that influences sweet potato yield and quality. The most important viruses for sweet potato are the sweet potato chlorotic stunt virus (SPCSV) of the genus Crinivirus and sweet potato feathery mottle virus (SPFMV) of the genus Potyvirus. SPCSV-infected sweet potato storage roots incline to develop severe viral disease at the seedling stage. However, the effect of whitefly (Bemisia tabaci) in sweet potato fields on the proportion of SPCSV-viruliferous storage roots and viral disease occurrence remains largely unknown. Here, we report that the amount of whitefly and the rate of SPCSV-viruliferous whiteflies in sweet potato fields were closely related to the viruliferous rate of storage roots. When there was a high number of viruliferous whiteflies in sweet potato fields, a high rate of viruliferous storage roots were triggered, even though virus-free sweet potato cuttings that would not induce severe symptoms in above ground plants had been planted. The SPCSV infection rate and double infection of storage roots with SPCSV and SPFMV presented significant positive correlations with the virus-like symptom rate in sprouts generated from the storage roots. The symptom rate in sprouts can be predicted by the viruliferous rate of storage roots.

Study on virus content of wheat yellow mosaic disease at different disease grade

2024-02-20 00:00:00.0

In order to clarify the variation of virus content of wheat yellow mosaic virus (WYMV) in various disease grade and tissue parts, wheat samples with typical incidence levels of 0, 1, 2 and 3 were collected from fields with uniform incidence of wheat yellow mosaic disease. Healthy wheat samples from virus-free fields were used as blank control. The absolute quantification of the content of wheat yellow mosaic virus in roots, stems and leaves was carried out by real-time fluorescent quantitative PCR (RT-qPCR). The results showed that the content of WYMV in wheat roots was significantly higher than that in leaves (P<0.05), and the virus content in wheat roots of grade 0 was 13.97 times higher than that in leaves. In wheat tissues of different disease grade, the virus content in roots, stems and leaves increased significantly with the aggravation of disease grade (P<0.05). The virus content in roots increased rapidly and then slowed down. From grade 0 to grade 1, the virus content in roots increased by 3.95×10⁶ copies·μL^-1L. However, from grade 1 to grade 3, the virus increase was only 1.45×10⁶copies·μL^-1. The virus content in stems and leaves showed a trend of uniform increase, and there was a strong positive correlation between the virus content in stems and the disease grade (R²=0.996 7). This study confirmed that the root is the key tissue site of WYMV virus infection in wheat. At the same time, it was found that the content of WYMV in the roots of diseased grade 0 wheat was much higher than that in the control group. The content of WYMV in the stem correlates closely with viral symptoms. The higher the content of stem virus, the more obvious the symptom of wheat.