Paenibacillus polymyxa SQR-21 systemically affects root exudates of watermelon to decrease the conidial germination of Fusarium oxysporum f.sp. niveum

Paenibacillus polymyxa SQR-21 has been identified as a potential agent for the biocontrol of Fusarium wilt in watermelon, which is caused by the pathogenic fungus Fusarium oxysporum f.sp. niveum (FON). In the present study, the effects of root exudates from watermelon plants inoculated or non-inoculated with either SQR-21 or FON on conidial germination of FON were investigated. Compared to the control, conidial germination was decreased with root exudates from SQR-21-inoculated plants, but conidial germination was enhanced by root exudates from FON-inoculated plants. Maximal germination was found with root exudates from FON-inoculated plants after 30 d, which was 1.35 times more germination than the control. A split-root system was designed to verify that the alterations of the exudation pattern in SQR-21- inoculated or FON-inoculated watermelon roots were not only local, but also systemic. Cinnamic acid was found in the watermelon root exudates. An assay to test the effects of cinnamic acid on conidial germination of FON revealed that the stimulation of conidial germination was observed from cinnamic acid concentrations ranging from 0 to 30 μg/ml. In conclusion, both of SQR-21 and FON systemically affects watermelon root exudates. These results will help to the better understanding of the plant-microbe communication and will guide to improve the biocontrol strategies against Fusarium wilt of watermelon plants.     

Volatile organic compounds produced by Lysinibacillus sp. FJAT-4748 possess antifungal activity against Colletotrichum acutatum

FJAT-4748 is a bacterial strain isolated from forest soil samples taken from Dongba Valley, Lijiang, Kunming, Yunnan Province, PR China. This strain was identified as Lysinibacillus sp. based on a 16S rRNA gene sequence analysis. FJAT-4748 has been shown to possess antifungal activity against different fungi, including Colletotrichum acutatum, Aspergillus niger, Fusarium solani, Fusarium moniliforme and Fusarium oxysporum. The results of the present study indicate that this antifungal activity results from volatile organic compounds (VOCs) produced by this strain. The observed inhibition rates of VOCs from FJAT-4748 against these fungi were 100%, 100%, 37.20%, 18.94% and 7.64%, respectively. GC-MS analysis identified 24 VOCs from FJAT-4748, which included different categories of compounds, such as aldehydes, ketones, alcohols, aromatic hydrocarbons and alkanes. Of these 24 VOCs, the most abundant compound was 2-ethyl-1-hexanol, which constituted 36.24% of the total VOCs based on the relative peak area. In the in vitro C. acutatum mycelial growth assay, 2-ethyl-1-hexanol exhibited the strongest activity, with an inhibitory rate of 100% using 10?µL/plate of this VOC. The activity of benzaldehyde was lower. 2-decanone showed the weakest activity among the compounds tested. The inhibitory activity of an artificial mixture of three VOCs against the C. acutatum increased with the amount of artificial mixture used. The inhibition rate reached 100% using 30?µL/plate of this artificial mixture in the plate test. Taken together, these results show that the antifungal VOCs produced by Lysinibacillus sp. FJAT-4748 are potentially useful as agents for controlling anthracnose caused by Colletotrichum acutatum.     

Root exudates of mycorrhizal tomato plants exhibit a different effect on microconidia germination of Fusarium oxysporum f. sp. lycopersici than root exudates from non-mycorrhizal tomato plants

The effect of root exudates from mycorrhizal and non-mycorrhizal tomato plants on microconidia germination of the tomato pathogen Fusarium oxysporum f. sp. lycopersici was tested. Microconidia germination was enhanced in the presence of root exudates from mycorrhizal tomato plants. The more tomato plants were colonized by the arbuscular mycorrhizal fungus Glomus mosseae, the more microconidia germination was increased, indicating that alterations of the exudation pattern depended on the degree of root AM colonization. Moreover, alterations of the exudation pattern of mycorrhizal plants are not only local, but also systemic. Testing the exudates from plants with a high and a low P level revealed that the alterations of the root exudates from mycorrhizal plants, resulting in a changed effect on microconidia germination, are not due to an improved P status of mycorrhizal plants.     

白色麝香霉挥发性有机化合物的抗菌活性和组成分析

采用核糖体RNA转录间隔区(internal transcribed spacer of ribosomal RNA,ITS r RNA)、RNA聚合酶II(RNA polymerase II,rpb2)和β-维管蛋白(beta-tubulin,tub1)基因系统发育分析法,鉴定了一株分离自浙江庆元的麝香霉ZJQY709,鉴定结果表明该菌为白色麝香霉Muscodor albus。生长速率法测定结果显示该菌株最适生长温度为22–28℃。二分格培养皿对峙培养法测定该菌挥发性有机化合物的抑菌活性,结果表明其挥发性有机化合物对灰葡萄孢菌和立枯丝核菌的生长抑制作用较强,而对尖孢镰刀菌和终极腐霉的抑制作用较弱。固相微萃取/气质联用法分析该菌产生的挥发性有机化合物,结果显示其挥发性有机化合物成分复杂,主要气体成分为2-甲基丙酸、乙酸-2-甲基丙酯和1-丁醇-2-甲基乙酸。     

Vibrational, 1H-NMR spectroscopic,and thermal characterization of gladiolus root exudates in relation to Fusarium oxysporum f. sp. gladioli resistance

Fourier transform Raman (FT Raman) and IR (FTIR) and (1)H-NMR spectroscopies coupled with differential scanning calorimetry (DSC) were applied to the characterization of root exudates from two cultivars of gladiolus (Spic Span and White Prosperity) with different degrees of resistance and susceptibility to Fusarium oxysporum gladioli, the main pathogen of gladiolus. This work was aimed at correlating the composition of root exudates with the varietal resistance to the pathogen. Spectroscopic analysis showed that White Prosperity root exudate differs from Spic Span root exudate by a higher relative amount of the aromatic-phenolic and sugarlike components and a lower relative amount of carbonylic and aliphatic compounds. DSC analysis confirmed the spectroscopic results and showed that White Prosperity root exudate is characterized by an aromatic component that is present in a higher amount than in the Spic Span root exudate. The results are discussed in relation to the spore germination tests showing that White Prosperity, which is characterized by a remarkable resistance toward F. oxysporum gladioli, exudes substances having a negative influence on microconidial germination of the pathogen; root exudates from Spic Span, one of the most susceptible cultivars to F. oxysporum gladioli, proved to have no effect. White Prosperity's ability to inhibit conidial germination of F. oxysporum gladioli can be mainly related to the presence of a higher relative amount of aromatic-phenolic compounds.     

Biocontrol of toxinogenic Aspergillus flavus and Fusarium oxysporum f. sp. albedinis by two rare Saharan actinomycetes strains and LC-ESI/MS-MS profiling of their antimicrobial products

Fungi colonizing fruits in the field and post-harvest constitute a major threat to the global food sector. This study focuses on the biocontrol of Aspergillus flavus (aflatoxin-producing mold considered carcinogenic by IARC) and Fusarium oxysporum f. sp. albedinis (FOA) (phytopathogenic agent, causal of El Bayoud in the Algerian and Moroccan Sahara). These molds have a significant economic impact and pose a serious human health problem. The aim of this work is to study the antifungal activity of two rare actinomycetes strains; Saccharothrix sp. COL22 and Actinomadura sp. COL08 strains against toxinogenic A. flavus and F. oxysporum f. sp. albedinis. The strains are isolated from Citrullus colocynthis rhizosphere on different media: ISP2, GLM, TSA, Starch-casein-agar and WYE and with different treatments of the samples (physical, chemical treatment and enrichment). The antifungal tests against the pathogenic microorganisms were performed on ISP2, GLM and TSA medium by means of the agar cylinders method. The kinetics of antibiotic production were performed on ISP medium over 16 days. The characterization of the antimicrobial compounds by LC-ESI/MS-MS showed that the bacterial extracts contain Antibiotic SF 2738C, Tetrodecamycin and Aplysillamide B. The phenotypic and molecular studies showed that Saccharothrix sp. COL22 is closely related to the Saccharothrix longispora strain type and that Actinomadura sp. COL08 is closely related to the Actinomadura hibisca strain type. The two strains are rare and showed an interesting activity against toxinogenic A. flavus and F. oxysporum f. sp. albedinis.