Molecular and Pathogenic Characterization of Fusarium redolens, a New Causal Agent of Fusarium Yellows in Chickpea

Newly isolated Brevundimonas naejangsanensis as a biocontrol agent against Fusarium redolens the causal of Fusarium yellows of chickpea

Three endophytic bacteria, namely BvV, BvP and BvL, were newly isolated from the root nodules of bean, pea and lentil plants respectively cultivated in Mascara the northwest of Algeria, and identified by 16S ribosomal RNA gene sequencing as Brevundimonas naejangsanensis. These strains were able to produce hydrolytic enzymes and hydrogen cyanide. All strains produced a growth-promoting hormone, indole acetic acid, varying in concentration from 83.2 to 171.7 µg/mL. The phosphate solubilizing activity of BvV, BvP and BvL varied from 25.5 to 42.02 µg/mL for tricalcium phosphate. The three antagonistic Brevundimonas spp. showed in vitro the most inhibitory effect on mycelial growth of Fusarium redolens FRC (from 78.33 to 85.55%). Strain BvV, BvP and BvL produced also volatile metabolites which inhibited mycelial FRC growth up to 39.2%. All strains showed significant disease reduction in pot experiments. Chickpea Fusarium yellows severity caused by FRC was reduced significantly from 89.3 to 96.6% in the susceptible cultivar ILC 482 treated with antagonistic B. naejangsanensis. The maximum stimulatory effect on chickpea plants growth was observed by inoculation of strain BvV. This treatment resulted in a 7.40-26.21% increase in shoot height as compared to the control plants. It is concluded that the endophytic bacterial strains of B. naejangsanensis having different plant growth promoting (PGP) activities can be considered as beneficial microbes for sustainable agriculture. To our knowledge, this is the first report to use B. naejangsanensis strains as a new biocontrol agent against F. redolens, a new pathogen of chickpea plants causing Fusarium yellows disease in Algeria.

Identification and Pathogenicity of Fusarium Isolated from Soybean in Poland

Fungi belonging to the Fusarium genus are commonly isolated from soybean plants and seeds but not all of them are pathogenic. The aim of this study was to compare the pathogenicity among different Fusarium isolates obtained from soybean plants with disease symptoms originating from an experimental field located in the southeast of Poland. Nineteen fungal isolates were selected for the pathogenicity assay, including eight isolates of F. oxysporum, six isolates of F. graminearum, four isolates of F. culmorum and one isolate of F. redolens. Species identification of these isolates was carried out using microscopic methods and sequencing of two genes: translation elongation factor 1-alpha (TEF1) and RNA polymerase second largest subunit (RPB2). To our knowledge, this is the first report of F. redolens being isolated from soybean in Europe. The pathogenicity test was set up by fungal inoculation of healthy soybean seeds of three cultivars: Abelina, Atlanta and Mavka. Symptoms were assessed seven days after inoculation. Disease area percentage of Fusarium inoculated seeds was significantly higher compared to uninoculated control. Nineteen isolates differed in their aggressiveness as the median disease area percentage ranged between 5.0 and 88.0% depending on isolate. The obtained isolates of four Fusarium species may be used in the future screening of soybean cultivars for resistance to these pathogens.

Diversity of Fusarium Species Isolated from Symptomatic Plants Belonging to a Wide Range of Agri-Food and Ornamental Crops in Lebanon

Lebanon is a small Mediterranean country with different pedoclimatic conditions that allow the growth of both temperate and tropical plants. Currently, few studies are available on the occurrence and diversity of Fusarium species on Lebanese crops. A wide population of Fusarium strains was isolated from different symptomatic plants in the last 10 years. In the present investigation, a set of 134 representative strains were molecularly identified by sequencing the translation elongation factor, used in Fusarium as a barcoding gene. Great variability was observed, since the strains were grouped into nine different Fusarium Species Complexes (SCs). Fusarium oxysporum SC and Fusarium solani SC were the most frequent (53% and 24%, respectively). Members of important mycotoxigenic SCs were also detected: F. fujikuroi SC (7%), F. sambucinum SC (5%), F. incarnatum-equiseti SC (3%), and F. tricinctum SC (4%). Two strains belonging to F. lateritium SC, a single strain belonging to F. burgessii SC, and a single strain belonging to F. redolens SC were also detected. This paper reports, for the first time, the occurrence of several Fusarium species on Lebanese host plants. The clear picture of the Fusarium species distribution provided in this study can pose a basis for both a better understanding of the potential phytopathological and toxicological risks and planning future Fusarium management strategies in Lebanon.

The Whole Genome Sequence of Fusarium redolens Strain YP04, a Pathogen that Causes Root Rot of American Ginseng

Fusarium redolens was previously reported as a plant pathogen or an endophyte that is closely related to F. oxysporum, a notoriously significant soilborne phytopathogen. Subsequent studies demonstrated the unique nature of F. redolens, which was considered a distinct species that causes multiple symptoms on multiple hosts. It was recently identified as a pathogen that causes root rot of American ginseng. Currently, few high-quality F. redolens genome sequences exist in the public database. Here, we report the whole-genome sequence of F. redolens strain YP04, based on a hybrid assembly of long- and short-read sequencing with PacBio and Illumina platforms, respectively. The assembly consists of 40 configs with a total length of 52.8 Mb nuclear genomic DNA and 49.6 kb complete mitochondrial genomic DNA, and encodes a total of 18,985 genes, including 18,517 protein-coding genes and 469 RNA genes which were functionally annotated. In total, 4,606 proteins were identified in the pathogen-host interactions database, suggesting that they were likely involved in pathogenicity and host-pathogen interactions, while 41 secondary metabolite synthesis clusters were predicted and annotated. This is the first high-quality whole genome of F. redolens, providing an important community resource for genome evolution, host-pathogen interaction, and secondary metabolite biosynthesis studies.

Combined Effects of Soil Biotic and Abiotic Factors, Influenced by Sewage Sludge Incorporation, on the Incidence of Corn Stalk Rot

The objectives of this study were to evaluate the combined effects of soil biotic and abiotic factors on the incidence of Fusarium corn stalk rot, during four annual incorporations of two types of sewage sludge into soil in a 5-years field assay under tropical conditions and to predict the effects of these variables on the disease. For each type of sewage sludge, the following treatments were included: control with mineral fertilization recommended for corn; control without fertilization; sewage sludge based on the nitrogen concentration that provided the same amount of nitrogen as in the mineral fertilizer treatment; and sewage sludge that provided two, four and eight times the nitrogen concentration recommended for corn. Increasing dosages of both types of sewage sludge incorporated into soil resulted in increased corn stalk rot incidence, being negatively correlated with corn yield. A global analysis highlighted the effect of the year of the experiment, followed by the sewage sludge dosages. The type of sewage sludge did not affect the disease incidence. A multiple logistic model using a stepwise procedure was fitted based on the selection of a model that included the three explanatory parameters for disease incidence: electrical conductivity, magnesium and Fusarium population. In the selected model, the probability of higher disease incidence increased with an increase of these three explanatory parameters. When the explanatory parameters were compared, electrical conductivity presented a dominant effect and was the main variable to predict the probability distribution curves of Fusarium corn stalk rot, after sewage sludge application into the soil.

Molecular phylogeny and diversity of Fusarium endophytes isolated from tomato stems

Plant tissues are a known habitat for two types of Fusarium species: plant pathogens and endophytes. Here, we investigated the molecular phylogeny and diversity of endophytic fusaria, because endophytes are not as well studied as pathogens. A total of 543 Fusarium isolates were obtained from the inside of tomato stems cultivated in soils mainly obtained from agricultural fields. We then determined partial nucleotide sequences of the translation elongation factor-1 alpha (EF-1α) genes of the isolates. Among the isolates from tomato, 24 EF-1α gene sequence types (EFST) were found: nine were classified as being from the Fusarium oxysporum species complex and its sister taxa (FOSC, 332 isolates), seven from the F. fujikuroi species complex (FFSC, 75 isolates) and eight from the F. solani species complex (FSSC, 136 isolates). To determine more characteristic details of the tomato isolates, we isolated 180 fusaria directly from soils and found 95% of them were nested within the FOSC (82 isolates; five EFSTs), FFSC (21 isolates; six FESTs) and FSSC (68 isolates; 11 EFSTs). These results suggested that the dominant Fusarium endophytes within tomato stems were members of the same three species complexes, which were also the dominant fusaria in the soils.

Genetic Diversity and Aggressiveness of Fusarium spp. Isolated from Canola in Alberta, Canada

Canola (Brassica napus) is one of the most economically important oilseed crops in Canada. Fusarium seedling blight is a root disease with the potential to cause severe yield reductions in canola. Fusarium spp. are commonly isolated root pathogens from fields in Alberta. Fusarium infection can also cause root rot in adult plants. In this study, 128 isolates identified as Fusarium spp. were recovered from field soils in central Alberta and from the roots of diseased canola plants with typical Fusarium seedling blight symptoms. Six species of Fusarium were identified, with Fusarium acuminatum as the predominant species (57 of 128 isolates, 44.5%). Phylogenetic analyses based on the translation elongation factor 1-α and the internal transcribed spacer sequence data were used for evaluation of genetic variations, and also used for Fusarium spp. identification in combination with morphological characteristics and polymerase chain reaction-based analyses. Based on disease ratings in pathogenicity tests, six isolates of F. avenaceum showed high aggressiveness on canola. Also, the aggressiveness varied within all Fusarium spp. No correlation was observed between aggressiveness and the geographic origin of the isolates.

Comparative Pathogenicity and Virulence of Fusarium Species on Sugar Beet

In all, 98 isolates of three Fusarium spp. (18 Fusarium oxysporum, 30 F. graminearum, and 50 Fusarium sp. nov.) obtained from sugar beet in Minnesota were characterized for pathogenicity and virulence on sugar beet in the greenhouse by a bare-root inoculation method. Among the 98 isolates tested, 80% of isolates were pathogenic: 83% of the F. oxysporum isolates, 57% of the F. graminearum isolates, and 92% of the Fusarium sp. nov. isolates. Symptoms varied from slight to moderate wilting of the foliage, interveinal chlorosis and necrosis, and vascular discoloration of the taproot without any external root symptoms. Among the pathogenic isolates, 14% were highly virulent and 12% were moderately virulent. Most of the highly virulent isolates (91%) and moderately virulent isolates (89%) were Fusarium sp. nov. All pathogenic isolates of F. graminearum and most pathogenic isolates (87%) of F. oxysporum were less virulent. In general, more-virulent isolates induced first foliar symptoms earlier compared with less-virulent isolates. This study indicates that both F. oxysporum and Fusarium sp. nov. should be used in greenhouse and be present in field studies used for screening and developing sugar beet cultivars resistant to Fusarium yellows complex for Minnesota and North Dakota.