Peanut root rot, caused by Fusarium spp., is a devastating fungal disease. As part of a program to obtain a biocontrol agent to control peanut root rot in the field, a bacterial strain LY-1 capable of inhibiting the growth of the fungus in vitro was isolated from rhizosphere soil samples collected from wild mint by agar disk dilution and dual-culture assay. Strain LY-1 was identified as Bacillus subtilis based on morphological characteristics, 16S rDNA, and gyrA sequence analyses. The bacterial suspension and cell-free culture filtrate of LY-1 could significantly inhibit the growth of Fusarium oxysporum, Fusarium proliferatum and Fusarium solani, but volatile organic compounds from the cultures had only a weak effect on mycelial growth. The percentage inhibition of 20% concentration of the cell-free culture filtrate of LY-1 on conidium production of each of the three Fusarium species was greater than 72.38%, and the percentage inhibition by the culture filtration on the germination of conidia of the three species was at least 62.37%. The production of extracellular enzyme activity by LY-1 was studied in functional assays, showing protease, cellulase, amylase, chitinase, and β-1,3-glucanase activity, while LY-1 contained a gene encoding iturin, an antifungal lipopeptide. In addition, under pot culture in a greenhouse, culture filtrate of LY-1 significantly promoted the growth of peanut, increasing the fresh and dry mass of the plant by 30.77% and 27.27%, respectively, in comparison with the no-filtrate control. The culture filtrate of LY-1 increased the resistance of peanut plants to F. oxysporum, with the biocontrol efficiency reaching 44.71%. In conclusion, B. subtilis LY-1, a plant-growth-promoting rhizobacterium, was able to protect peanuts from Fusarium spp. infection.

Peanut (Arachis hypogaea L.) is one of the most economically important crops as an important source of edible oil and protein. In August 2020, circular to oval-shaped brown leaf spots (2-6 mm in diameter) with well-defined borders surrounded by a yellow margin were observed on peanut plant leaves in Laixi City, Shandong Province, China. Symptomatic plants randomly distributed in the field, the incidence was approximately 5%. Leave samples were collected consisted of diseased tissue and the adjacent healthy tissue. The samples were dipped in a 70% (v/v) ethanol solution for 30 s and then soaked in a 0.1% (w/v) mercuric chloride solution for 60 s. The surface-sterilized tissues were then rinsed three times with sterile distilled water, dried and placed on Czapek Dox agar supplemented with 100 μg/ml of chloramphenicol. The cultures were incubated in darkness at 25 °C for 3-5 days. Fungal colonies were initially white and radial, turning to orange-brown in color, with abundant aerial mycelia. Macroconidia were abundant, 4 to 7 septate, with a dorsiventral curvature, and were 3.3-4.5 × 18.5-38.1 μm (n=100) in size; microconidia were absent; chlamydospores were produced in chains or clumps, ellipsoidal to subglobose, and thick walled. The morphological characteristics of the conidia were consistent with those of Fusarium spp. To identify the fungus, an EasyPure Genomic DNA Kit (TransGEN, Beijing, China) was used to extract the total genomic DNA from mycelia. The internal transcribed spacer region (ITS rDNA) and the translation elongation factor 1-α gene (TEF1) were amplified with primers ITS1/ITS4 (White et al. 1990) and EF1/EF2 (O'Donnell et al. 1998), respectively. Based on BLAST analysis, sequences of ITS (MT928727) and TEF1 (MT952337) showed 99.64% and 100% similarity to the ITS (MT939248.1), TEF1 (GQ505636.1) of F. ipomoeae isolates. Sequence analysis confirmed that the fungus isolated from the infected peanut was F. ipomoeae (Xia et al. 2019). The pathogenicity of the fungus was tested in the greenhouse. Twenty two-week-old peanut seedlings (cv. Huayu20) grown in 20-cm pots (containing autoclaved soil) were sprayed with a conidial suspension (105 ml-1) from a 15-day-old culture. Control plants were sprayed with distilled water. The experiment was conducted as a randomized complete block design, and placed at 25 °C under a 12-h photoperiod with 90% humidity. Symptoms similar to those in the field were observed on leaves treated with the conidial suspension ten days after inoculation, but not on control plants. F. ipomoeae was re-isolated from symptomatic leaves but not from the control plants. Reisolation of F. ipomoeae from inoculated plants fulfilled Koch's postulates. To our knowledge, this is the first report of F. ipomoeae causing peanut leaf spot in China. Our report indicates the potential spread of this pathogen in China and a systematic survey is required to develop effective disease management strategies.

Peanut (Arachis hypogaea L.) is one of the most economically important crops as a major source of edible oil and protein. In July 2021, a root rot disease was observed on peanut in Laiwu (36º22' N,...

Peanut (Arachis Hypogaea) is a globally important crop for food and oil extraction. In recent year, the rot-like symptoms were observed on peanut pods in Shandong and Henan provinces, the main peanut producing areas. Brown to black lesions were seen primarily on infected pods and kernels. From August to November in 2018, samples of pods were collected from ten peanut producing areas in five provinces. Pieces of pod rot symptomatic tissue (5 mm2) were cut from the pods, surface sterilized with 0.5% NaClO, rinsed with sterile water, dried on a paper towel, then plated on 2.5% vegetable (V8) juice medium. The plates were incubated at 25 °C for 2 –3 days in the dark. White fungal colonies with non-septate mycelia grew from the tissue pieces. Single hyphal tip cultures were placed on corn meal agar (CMA) containing rifampicin (50 mg/l), phenamacril (5mg/l), ampicillin (50mg/l), and pentachloronitrobenzene (50mg/l) (Chen et al., 2017). Seven isolates with similar morphological characteristics were obtained. The...