Fusarium oxysporum,F. proliferatum and F. redolens associated with basal rot of onion in Finland

In recent years in Finland, Fusarium infections in onions have increased, both in the field and in storage, and Fusarium species have taken the place of Botrytis as the worst pathogens causing post‐harvest rot of onion. To study Fusarium occurrence, samples were taken from onion sets, harvested onions and also from other plants grown in the onion fields. Isolates of five Fusarium species found in the survey were tested for pathogenicity on onion. Fusarium oxysporum was frequently found in onions and other plants, and, of the isolates tested, 31% caused disease symptoms and 15% caused growth stunting in onion seedlings. Fusarium proliferatum, a species previously not reported in Finland, was also identified. Over 50% of the diseased onion crop samples were infected with F. proliferatum, and all the F. proliferatum isolates tested were pathogenic to onion. Thus, compared to F. oxysporum, F. proliferatum seems to be more aggressive on onion. Also some of the F. redolens isolates were highly virulent, killing onion seedlings. Comparison of the translation elongation factor 1α gene sequences revealed that the majority of the aggressive isolates of F. oxysporum f. sp. cepae group together and are distinct from the other isolates. Incidence and relative proportions of the different Fusarium species differed between the sets and the mature bulbs. More research is required to determine to what extent Fusarium infections spoiling onions originate from infected onion sets rather than the field soil.     

Fusarium proliferatum, an additional bulb rot pathogen of Chinese chive

This is the first report of a disease of Chinese chive caused by Fusarium proliferatum. Because the symptoms are similar to those of the bulb rot (kampu-byo in Japanese) caused by F. oxysporum, we propose F. proliferatum as another causal agent of bulb rot of Chinese chive. Symptoms are wilting of leaves and brown rot on the basal bulbs of Chinese chive. A Fusarium sp., frequently isolated from symptomatic plants, produced identical symptoms on Chinese chive after inoculation, and was reisolated from the diseased plants. The fungus was identified as F. proliferatum based on morphological, cultural, and molecular characteristics.     

Determination of seedborne fungi in Onion and their transmission to Onion sets

Samples of onion (Allium cepa L.) seeds were obtained from seven regions in Turkey. The seed coat, embryo and endosperm were cultured, the seedborne fungi were determined and their transmission to onion sets was investigated in both sterile and field soils. Among the fungi determined,Aspergillus alutaceus Berk, and Curt.,Beauveria bassiana (Bals.) Vuill.,Cladosporium cladosporioides (Fres.) de Vries,Geotrichum sp.,Humicola fuscoatra Traaen,Trichoderma harzianum Rifai andT. pseudokoningii Rifai in onion seeds, andFusarium culmorum (W.G.Sm.) Sacc,F. graminearum Schwabe andF. sambucinum Fuckel in onion sets, were recorded for the first time.Aspergillus niger v. Tieghem was found at the highest rate in seed samples (especially in the seed coat), and in bulbs and roots of onion sets that developed from these seeds, whether in sterile or field soil.Fusarium oxysporum Schlecht was isolated at a higher rate from onion sets grown in sterile or field soil, than from seeds.F. acuminatum Ellis and Everhart,F. sambucinum, F. equiseti (Corda) Sacc. andF. graminearum were isolated only from onion sets grown in sterile soil. In dual culture tests, theseFusarium isolates were inhibited byA. niger and thus, exceptfor F. oxysporum, could not develop in agar plate. TheFusarium spp. appeared in onion-sets grown in sterile soil and were inhibited by other fungi in field soil. It was concluded that all fungi were seedborne and thatA. niger andFusarium spp., but not the other fungi, were transmitted from the seeds to onion sets.A. niger andF. oxysporum were also transmitted through the soil.     

Genetic variation among <Emphasis Type="Italic">Fusarium</Emphasis> isolates from onion,and resistance to <Emphasis Type="Italic">Fusarium</Emphasis> basal rot in related <Emphasis Type="Italic">Allium</Emphasis> species

The aim of this research was to study levels of resistance to Fusarium basal rot in onion cultivars and related Allium species, by using genetically different Fusarium isolates. In order to select genetically different isolates for disease testing, a collection of 61 Fusarium isolates, 43 of them from onion (Allium cepa), was analysed using amplified fragment length polymorphism (AFLP) markers. Onion isolates were collected in The Netherlands (15 isolates) and Uruguay (9 isolates), and received from other countries and fungal collections (19 isolates). From these isolates, 29 were identified as F. oxysporum, 10 as F. proliferatum, whereas the remaining four isolates belonged to F. avenaceum and F. culmorum. The taxonomic status of the species was confirmed by morphological examination, by DNA sequencing of the elongation factor 1-α gene, and by the use of species-specific primers for Fusarium oxysporum, F. proliferatum, and F. culmorum. Within F. oxysporum, isolates clustered in two clades suggesting different origins of F. oxysporum forms pathogenic to onion. These clades were present in each sampled region. Onion and six related Allium species were screened for resistance to Fusarium basal rot using one F. oxysporum isolate from each clade, and one F. proliferatum isolate. High levels of resistance to each isolate were found in Allium fistulosum and A. schoenoprasum accessions, whereas A. pskemense, A. roylei and A. galanthum showed intermediate levels of resistance. Among five A. cepa cultivars, ‘Rossa Savonese’ was also intermediately resistant. Regarding the current feasibility for introgression, A. fistulosum, A. roylei and A. galanthum were identified as potential sources for the transfer of resistance to Fusarium into onion.     

Identification of differential resistance to six Fusarium oxysporum f. sp. cepae isolates in commercial onion cultivars through the development of a rapid seedling assay

Fusarium oxysporum isolates collected from onions in the UK and other countries were characterized using sequences of the transfer elongation factor 1‐α (TEF) gene and compared with published sequence data for 10 other isolates. Isolates associated with diseased onion bulbs in the UK formed two clades. Isolates from both clades were selected for pathogenicity testing and to develop a rapid seedling assay to screen commercial onion cultivars for resistance to F. oxysporum f. sp. cepae (FOC), the cause of basal rot. Differences in the levels of aggressiveness between isolates were observed and isolates from both clades were pathogenic. Differences in resistance/susceptibility were also observed amongst 10 commercial onion cultivars, with cvs Ailsa Craig Prizewinner and White Lisbon showing the highest levels of resistance. The results from the seedling assay were supported by those from a subsequent onion bulb rot assay. Thus, this study reports the development of a rapid, simple and repeatable seedling assay that can be used to screen large numbers of onion cultivars for resistance to FOC and which is indicative of resistance at the bulb stage.     

Fusarium oxysporum- und F. proliferatum-Isolate aus Spargel und deren Pathogenit?ts��berpr��fung in einer modifizierten in vitro-Schnelltestmethode

Fusarium oxysporum and Fusarium proliferatum are important causal agents of crown and root rot of asparagus. In order to detect differences in pathogenicity and aggressiveness, two F. proliferatum and five F. oxysporum single spore isolates from asparagus spears from plantings in Austria and Germany, 55 pure cultures of F. oxysporum from asparagus roots from a planting in Hesse, Germany, and a single F. oxysporum isolate from an asparagus shoot collected in Austria were evaluated in a 28-day quick test on Hoagland??s agar in glass culture tubes. Plantlets were inoculated with spore suspensions from each respective isolate after 14 days of growth under sterile, controlled conditions in a growth chamber. A severity scale was used to assess symptoms on roots two weeks after inoculation. The effects of the single-spore isolates on root and shoot fresh weights of the plantlets were also determined. The pathogenicity of the majority of the F. proliferatum and F. oxysporum isolates included in this study was confirmed. Inoculation with pure and single-spore cultures resulted in elevated disease severity in comparison to non-inoculated controls. In particular, the two F. proliferatum isolates were found to be more aggressive than the F. oxysporum isolates. Moreover, all single spore isolates caused a reduction in fresh weight of roots and shoots in comparison to the controls. With respect to differences among asparagus cultivars, ??Ramos??, was found to be more susceptible than ??Ravel??. Overall, the quick test method was found to be capable of evaluating the pathogenicity and aggressiveness of the tested F. oxysporum and F. proliferatum isolates towards asparagus within 28 days.     

A selective agar medium for isolation,enumeration and morphological identification of Fusarium proliferatum

A selective agar medium based on macerated date fruits was developed for the isolation, enumeration and morphological identification of Fusarium proliferatum from soil and from infected tissues of various plants (including: onion bulbs, corn ears and stems, and various weed tissues). The selective date medium enhances the formation of polyphialide and longer chains of conidia for better separation from other related Fusarium species which also grow and proliferate on this medium. Furthermore, the date medium enables microscopic distinction among other closely related Fusarium species, e.g. F. oxysporum and F. verticillioides. Fruits of the date cultivars Medjoul and Deglet Noor provided the most useful results as compared with other cultivars tested. The date medium can serve as a selective medium for direct isolation and enumeration of F. proliferatum, as it suppresses the development of other soil fungi and plant pathogens such as Macrophomina phaseolina, Sclerotium rolfsii and Rhizoctonia solani, as well as bacteria.     

Molecular identification and mycotoxin production of <Emphasis Type="Italic">Lilium longiflorum</Emphasis>-associated fusaria isolated from two geographic locations in the United States

Fusarium diseases of Liliaceae crops cause significant losses worldwide. Yet some Fusarium species are found in planta without causing disease or even in a symbiotic relationship with its host. In this study we identified and characterized the Fusarium species isolated from soil, and from healthy and diseased bulbs of Lilium longiflorum grown in New Jersey and Oregon in the United States. The predominant Fusarium species from the Oregon location were F. solani (74%) and F. oxysporum (20%), whereas F. concentricum (43%) and F. proliferatum (26%), both belonging to the Gibberella fujikuroi species complex (GFSC), were the most commonly isolated species from New Jersey. To our knowledge, this is the first report of F. concentricum associated with Liliaceae. All of the isolates were characterized with sequences of the internal transcribed spacer and translation elongation factor 1-alpha genes. The 24 GFSC isolates were further characterized with mating type, mating population, and mycotoxin analysis. Results showed that all GFSC isolates were MAT-2, suggesting that the populations may be asexually reproducing in the region examined. The majority of the GFSC isolates produced beauvericin. Enniatin A, B, B₁ and fusaproliferin were produced by a few isolates. Enniatin A₁ and fumonisins were not detected in any of the isolates. Although F. oxysporum and F. solani are well-known bulb pathogens, many isolates of F. oxysporum and F. solani, and all of the F. concentricum and F. proliferatum were isolated from asymptomatic bulbs, suggesting their endophytic association with lilies.     

Morphological and molecular identification and PCR amplification to determine the toxigenic potential of Fusarium spp. isolated from maize ears in southern Poland

The average amount of precipitation in spring and summer 2010 and 2011 coupled with relatively high temperatures caused massive Fusarium spp. infection of maize and yield losses in southern Poland. In order to examine the cause of this disease outbreak, Fusarium spp. were isolated and fungal strains were identified based on morphological characters and species-specific PCR assays. A total of 200 maize samples were processed, resulting in the obtention of 71 strains, which belonged to five Fusarium species, F. poae being the predominant one (74.56%). Other isolates were identified as F. graminearum, F. oxysporum, F. verticillioides and F. proliferatum. PCR-based detection of mycotoxin-synthesis-pathway genes was also used to determine the potential of the analyzed strains to produce trichothecenes (DON and NIV) and fumonisins (FUM). Only 14 isolates revealed the potential to produce DON (11 strains) and FUM (3 strains). HPLC analyses of grain samples revealed the presence of DON only – other mycotoxins were not detected. Moreover, 57.1% of potentially mycotoxin-producing isolates indicated the toxicity in a biological test.     

Fusarium oxysporum schlecht. in Israel

Out of 208 isolates ofF. oxysporum, 158 produced toxic reactions when applied to rabbit skin. This fungus, ubiquitous in the soils of Israel, was the most prevalent component of theFusarium flora in the unirrigated (but not in the irrigated) soils sampled.F. oxysporum var.redolens was common only on unfertilized plots of heavy, unirrigated soils.F. oxysporum was a major constituent of theFusarium flora isolated from most of the 450 samples of 20 field and garden crops, but less common in 98 samples of citrus, avocado and mango fruits. It ranks among the most destructive pathogens of cucurbits (exceptCucurbita pepo), tomatoes, onions, and gladioli in Israel, but causes almost no damage to Brassicae, peas or cotton. In pathogenicity tests with 207 isolates from nine field and two fruit crops, numerous isolates caused seedling mortality, with watermelon, onion, cucumber, tomato and eggplant being the most susceptible. Spore measurements on 160 isolates from plants and 355 from soils, showed that spore size was not markedly affected by plant source or by irrigation, but did differ between soil samples taken at 5 and 20 cm depth, and from manured or unfertilized soils.     

Occurrence of bacterial rot of onion caused by Bacillus amyloliquefaciens in Korea

In 2008, bacterial rot on onion bulbs (Allium cepa L.) was observed in several low-temperature warehouses in Changnyeong-gun, Korea. The causal pathogen was isolated and identified as Bacillus amyloliquefaciens based on morphological and biochemical characterization and sequence analysis of its genome. The isolated bacteria caused the same rot symptom on inoculated onion bulbs as found in naturally infected onions during storage and was reisolated from these bulbs. This is the first report of bacterial rot of onion caused by B. amyloliquefaciens in Korea.     

Pathogenicity and mycotoxin production by <Emphasis Type="Italic">Fusarium proliferatum</Emphasis> isolated from onion and garlic in Serbia

Fusarium proliferatum can occur on a wide range of economically important vegetable plants but its role in disease is not always well established. In 2000 and 2001, from forty-one field samples of wilting onion and garlic plants in Serbia, F. proliferatum as the predominant fungal species was isolated from root and bulbs. Seventy isolates were firstly characterized for their sexual fertility and were shown to be mostly members of Gibberella intermedia (sixty-seven of seventy isolates, the remaining three isolates were unfertile), the sexual stage of F. proliferatum (syn. mating population D of G. fujikuroi complex). A selected set of eleven F. proliferatum isolates from both hosts were also tested for their pathogenicity and toxigenicity. Although onion and garlic plants were susceptible to all isolates, onion plants showed a significantly higher disease severity index. Six of the eleven isolates of F. proliferatum produced fumonisin B₁ from 25 to 3000 μg g⁻¹, and beauvericin from 400 to 550 μg g⁻¹; ten isolates produced fusaric acid from 80 to 950 μg g⁻¹ and moniliformin from 50 to 520 μg g⁻¹. Finally, all isolates produced fusaproliferin up to 400 μg g⁻¹. These results confirm F. proliferatum as an important pathogen of garlic and onion in Europe and that there is a potential mycotoxin accumulation risk in contaminated plants of both garlic and onion.     

Induced resistance against Fusarium diseases of <Emphasis Type="Italic">Cymbidium</Emphasis> species by weakly virulent strain HPF-1 (<Emphasis Type="Italic">Fusarium</Emphasis> sp.)

The mechanism by which Fusarium diseases of cymbidium plants are suppressed by a weakly virulent strain HPF-1 of Fusarium sp. was studied. Strain HPF-1 produced microscopic, necrotic local lesions on cymbidium leaves, causing minor damage to palisade tissues at the infection sites. This weakly virulent strain remained near the site of infection and did not develop further. It systemically and nonselectively suppressed some diseases of cymbidium such as yellow spot of leaves caused by Fusarium proliferatum and F. fractiflexum, bulb and root rot caused by F. oxysporum, and dry rot of bulbs and roots caused by F. solani. Because endogenous salicylic acid levels increased in cymbidium leaves inoculated with strain HPF-1, the mechanism of disease suppression is thought to be systemic acquired resistance.     

Conventional and real-time PCR for the identification of Fusarium fujikuroi and Fusarium proliferatum from diseased rice tissues and seeds

Fusarium fujikuroi is a species of the Gibberella fujikuroi species complex (GFSC) and the causal agent of bakanae disease on rice. Even if F. fujikuroi is the most abundant Fusarium species found on rice, other species can also be isolated from rice, such as F. proliferatum. Multiple alignment of translation elongation factor (TEF) gene sequences of different Fusarium spp., showed a deletion of six nucleotides in F. fujikuroi sequence and a two nucleotide polymorphism in the same region of F. proliferatum sequence. These elements of variability were used to develop a conventional and Real-Time PCR assay for diagnosis. The species specific primer pairs (Fuji1F/TEF1R and Proli1F/TEF1R) gave a product of 179 and 188?bp for F. fujikuroi and F. proliferatum respectively. Primer specificity was confirmed by analyzing the DNA of the most representative species of the GFSC and 298 strains of Fusarium spp. isolated from rice plants and seeds in Italy. The specific primers were also successfully used to detect fungal presence directly from infected rice tissues and seeds, providing a rapid tool for the early detection of pathogen contamination.     

Artenspektrum und Befallshäufigkeit von Fusarium spp. in Bt- und konventionellem Mais im Maiszünsler-Befallsgebiet Oderbruch

The European corn borer (Ostrinia nubilalis) is one of the most important pests of maize (Zea mays). Injuries to the plants caused by the larvae of the European corn borer may represent entrance gates for fungal-spores. The cultivation of Bacillus thuringiensis maize (Bt-maize) is one possibility to reduce infestation by the European corn borer. The aim of the present project was to determine and to compare the number of species and the frequency of Fusarium spp. infestation in Bt-maize (cry1Ab) and conventional maize. In 2003, we analysed the Fusarium spp. infestation of samples of chaffed Bt-maize and its isogenic variety on two experimental fields in the Oderbruch region (Germany), an European corn borer infested area. The conventional variety on the first of the experimental fields (previous crop wheat and forking cultivation) showed a small infestation (16%) of Ostrinia nubilalis while in the conventional variety on the second field (previous crop maize and not forking cultivation) the infestation of the European corn borer was almost three times higher (47%). In the conventional variety on both of the experimental fields we found a high Fusarium spp. infestation (70%). Especially species of the section Liseola dominates, among them: F. subglutinans, F. proliferatum und F. verticillioides. The Fusarium infestation in the samples of Bt-maize from the field with previous crop wheat and forking cultivation was just as high as in the conventional variety (70%). The infestation of Fusarium spp. in the samples of Bt-maize from the field with previous crop maize and forking cultivation was more than 20?% lower.     

Pathogenic variation and molecular characterization of <Emphasis Type="Italic">Fusarium</Emphasis> species isolated from wilted Welsh onion in Japan

Thirty-two isolates of Fusarium species were obtained from wilted Welsh onion (Allium fistulosum) grown on nine farms from six regions in Japan and identified as F. oxysporum (18 isolates), F. verticillioides (7 isolates), and F. solani (7 isolates). The pathogenicity of 32 isolates was tested on five commercial cultivars of Welsh onion and two cultivars of bulb onion in a seedling assay in a greenhouse. The Fusarium isolates varied in the degree of disease severity on the cultivars. Five F. oxysporum isolates (08, 15, 17, 22, and 30) had a higher virulence on the cultivars than the other isolates. The host range of these five isolates was limited to Allium species. Molecular characterization of Fusarium isolates was performed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis of the internal transcribed spacer (ITS) regions of ribosomal DNA. The 32 isolates were grouped into eight types (four types for F. oxysporum, one for F. verticillioides, and three for F. solani). Restriction patterns of the ITS region were not related to pathogenicity. However, the haplotypes obtained with five enzymes (RsaI, HinfI, HaeIII, ScrFI, and MspI) and the phylogenetic analysis permitted the discernment of the three Fusarium species. The PCR-RFLP analysis should provide a rapid, simple method for differentiating Fusaruim species isolated from wilted Welsh onion in Japan.     

Characterization of Fusarium diseases on commercially grown orchids in Hawaii

A decline of unknown aetiology has become a major problem for commercial orchid production in Hawaii, one of the primary orchid‐producing states in the USA. The major symptoms of decline include root degradation, foliar blight, pseudobulb rot and sheath rot. It was unclear whether all these symptoms are caused by the same or different pathogens, but preliminary research indicated that Fusarium species may be involved. In this study, the incidence of Fusarium species was examined across 186 plants, from 29 orchid genera and intergeneric hybrids across three islands in the state of Hawaii. The main five species associated with diseased orchids were F. proliferatum (38% of samples), F. solani (16%), F. oxysporum (16%) and two previously undescribed species (8% for both species combined). The two undescribed species were similar in appearance to F. subglutinans, and were designated FS‐A and FS‐B. Pathogenicity tests established that both F. proliferatum and FS‐B caused foliar spots, foliar blight and pseudostem rot on Dendrobium orchids, and that F. proliferatum isolates from diseased tissue of several genera could also induce symptoms on Dendrobium orchids. Although orchids have increasing importance in floriculture, relatively little is known about orchid pathogens, and previous studies focused primarily on Cymbidium and Phalaenopsis. This study provides new information concerning Dendrobium orchid pathogens and suggests a much wider host range than previously recognized for the five Fusarium species recovered from tissue with symptoms. These findings can contribute to better management of Fusarium diseases, which represent a significant challenge to orchid production in Hawaii.     

Fusarium Redolens f.sp asparagi, Causal Agent of Asparagus Root Rot, Crown Rot and Spear Rot

Two Fusarium species, F. oxysporum f.sp. asparagi and F. proliferatum, are known to be involved in the root and crown rot complex of asparagus. We have investigated reports on the involvement of F. redolens, a third species, which until recently was considered conspecific with F. oxysporum because of morphological similarities. RFLP analysis of the rDNA internal transcribed spacer region and AFLP fingerprinting identified eight strains from asparagus unambiguously as F. redolens. Four of these were tested and found to be pathogenic to asparagus either in this study (two strains) or in a previous one in which they were classified as F. oxysporum (three strains). Disease symptoms and disease development were the same as with F. oxysporum f.sp. asparagi and F. proliferatum. Present data and literature reports identify F. redolens as a host-specific pathogen involved in root, crown and spear rot of asparagus. The pathogen is formally classified as F. redolens Wollenw. f.sp. asparagi Baayen.     

Diversity of <Emphasis Type="Italic">Fusarium</Emphasis> species associated with root rot of sugar beet in China

Sugar beet is widely grown throughout the world and represents the second largest crop used to produce sugar. Root rot in sugar beet, caused by Fusarium, significantly reduces yield, juice purity, and sugar concentration. Here, 307 Fusarium isolates were collected from sugar beet roots exhibiting typical root rot symptoms in eight provinces or autonomous regions of China from 2009 to 2012. Based on morphological characteristics and sequence data of the internal transcribed spacer (ITS) region of ribosomal DNA (rDNA) and the translation elongation factor 1α (EF-1α), Fusarium oxysporum (38.4%) was identified as the most prevalent species, followed by F. solani (20.9%), and F. equiseti (18.9%). These three species were widely distributed in all eight of the provinces and autonomous regions. F. tricinctum (5.9%), F. brachygibbosum (4.6%), F. redolens (3.3%), F. proliferatum (3.3%), F. graminearum (2.3%), F. verticillioides (1.6%), F. nygamai (0.7%), and F. culmorum (0.3%) were less frequently obtained. Of the 307 Fusarium isolates, 117 representing different species and geographic locations were demonstrated to cause tip rot and vascular discoloration in sugar beet roots, with disease incidence ranging from 84.2 to 100.0% and disease index ranging from 41.94 to 75.83. This is the first detailed report of Fusarium species, in particular F. tricinctum, F. brachygibbosum, F. redolens, F. proliferatum, F. nygamai, and F. culmorum, causing sugar beet root rot in China.