Radiometric assessment of tillage and seed treatment effect on soybean root rot caused by Fusarium spp. in central Minnesota

Soybean root rot, caused primarily by Fusarium solani f. sp. phaseoli in a complex with F. oxysporum and Rhizoctonia solani, has become an increasing problem for soybeans, dry beans, and other rotation crops in central Minnesota due to soil conditions associated with reduced tillage. This study was conducted, in two field sites in central Minnesota located near Staples and Verndale, to develop methods for nondestructive assessment of root rot severity using plant radiometric properties. Soybean canopy reflectance was measured with a hand-held multi-spectral radiometer. Prior to the radiometer measurements, attempts were made to create differing root rot situations with moldboard or chisel tillage, and with or without a biological seed treatment. Root rot severity was estimated using a visual disease severity scale. Colony-forming units (CFU) were determined to estimate soil populations of pathogenic F. solani and F. oxysporum. Results from the Verndale site consistently showed significant treatment effects in the measured canopy radiometric parameters, and in the visual disease rating and yield (significant for seed treatment). Values of a simple ratio vegetation index from this site exhibited negative relationships with disease rating and F. oxysporum CFU, and a positive linear relationship with yield. Treatment effects were generally not significant at the Staples site because of low initial F. oxysporum populations. The results indicate that remote sensing is potentially a rapid, nondestructive means for assessment of root rot diseases in soybean.     

Analysis of interspecific relationships between Funneliformis mosseae and Fusarium oxysporum in the continuous cropping of soybean rhizosphere soil during the branching period

This study analysed the interspecific relationships between the dominant arbuscular mycorrhizal (AM) fungus, Funneliformis mosseae, and the major soybean root rot pathogen, Fusarium oxysporum, in the rhizosphere soil of continuous cropped soybean. Our aim was to provide theoretical evidence on the AM fungi to overcome the obstacles of soybean continuous cropping. We selected soybean cultivars, including Kenfeng 16 (an intermediate cultivar), Heinong 44 (a high-fat cultivar) and Heinong 48 (a high-protein cultivar), and sowed in the soybean continuous cropping soil under different treatments. The infection status of the soybean roots during the branching period by Fu. mosseae and F. oxysporum was estimated using the standard polymerase chain reaction method, as well as their colonisation status in rhizosphere soil. The AM fungal colonisation rates and F. oxysporum disease incidence of soybean roots were determined, respectively. Quantitative polymerase chain reaction was applied to analyse the DNA content of Fu. mosseae and F. oxysporum to investigate the relationship between Fu. mosseae and F. oxysporum. The results show that both Fu. mosseae and F. oxysporum can infect the soybean roots during the branching period and colonise the rhizosphere. However, the DNA content of F. oxysporum clearly decreased in soybean root and rhizosphere samples after the inoculation with Fu. mosseae. In addition, the disease incidence of F. oxysporum significantly decreased after inoculation with Fu. mosseae, which might indicate inhibitive effects of Fu. mosseae over F. oxysporum.     

Molecular characterisation of Fusarium oxysporum causing rot diseases in small cardamom (Elettaria cardamomum Maton)

Incidence of root rot and foliar yellowing, rhizome rot, panicle wilt and stem rot diseases of small cardamom (Elettaria cardamomum Maton) are caused by Fusarium oxysporum Schlecht., and were surveyed in the high ranges of Idukki district, Kerala during 2010–2011. The diseases were noticed in different areas to varying degrees. Root rot was found to be most severe, followed by pseudostem rot, rhizome rot and panicle wilt. The Fusarium infections were prevalent throughout the year (January–December) and varied from 1.5 to 10.6%. Even though the pathogen was isolated from different plant parts, during pathogenicity studies, all the isolates could cross-infect other plant parts too. Twenty different isolates of F. oxysporum were obtained from diseased samples, and five morphologically distinct isolates were analysed with Randomly Amplified Polymorphic DNA (RAPD) markers to study the genetic variability, if any, among them. PCR amplification of total genomic DNA with random oligonucleotide primers generated unique banding patterns, depending upon primers and isolates. Nine oligunucleotide primers were selected for the RAPD assays, which resulted in 221 bands for the five isolates of F. oxysporum. The number of bands obtained was entered into an NTSYS, and the results showed moderate genetic variability among F. oxysporum isolates causing root rot, rhizome rot, panicle wilt and pseudostem rot, collected from different locations. The dendrogram of different isolates into groups resulted in one major cluster at 0.61 similarity index comprising of four isolates (CRT 3, CRR 3, CPW 2 and CSR 1) and one isolate (CRT 5) formed in a separate cluster. Among the five isolates of F. oxysporum, CRT 5 was entirely different from the other four isolates. The isolates also differ according to the geographical area, as revealed from the genetic variability observed in different root rot isolates (CRT 3 and CRT 5). It is inferred that despite moderate variability, F. oxysporum, infecting small cardamom in Idukki district of Kerala, consists of a single clonal lineage.     

Effect of mycorrhiza and biofertilisers on reducing the incidence of Fusarium root and pod rot diseases of peanut

Pathogenicity tests of twenty-six fungal isolates were tested on peanut plants (Giza 5 cv.) and the results revealed that, Fusarium oxysporum isolate (No. I) followed by F. solani (No. II) then F. moniliforme (No III) significantly caused highest incidence of root rot disease. Also, F. moniliforme (No III) followed by F. solani (No II) then F. oxysporum (No I) gave the highest incidence of pod rot disease. The effectiveness of vescular arbuscular-mycorrhiza (VAM) at different application rates on the incidence of root rot, pod rot diseases and plant growth parameters of peanut was studied. All soil treatments with each rate of VAM significantly reduced root and pod rot diseases compared with control (rate 0%). The best reduction in the severity of both diseases with VAM was found at the rate of 3%. Application of rhizobacterin, microbin and cerialin biofertilisers at the different concentrations decreased the severity of both root rot and pod rot severity diseases compared with non-treated seeds. The greatest reduction in both diseases was achieved at a concentration of 8/100?g seeds. The highest number of pods and fresh weight (g) was achieved in seed supplemented with each biofertiliser at concentration of 8/100?g seed.     

Molecular characterization of Rhizoctonia solani isolates the incitant of soybean root rot

Rhizoctonia solani isolates used in this investigation were identified as anastomosis-4 (AG-40), collected from different localities from Assiut governorate in Egypt. Pathogenicity test of seven isolates of R. solani was evaluated on soybean Giza 111 cultivar under greenhouse conditions. All tested isolates were able to infect soybean plants causing root rot with different degrees of severities, isolate No. 1, 2 and 3 showed significantly highest root rot severity, while isolate No. 5 gave the lowest percentage of root rot rating. The sodium dodecyl sulphate polyacrylamide gel electrophoresis patterns were used to compare three isolates of R. solani. There are no variations among R. solani isolates except a few exceptions according to their protein patterns. DNA markers obtained from all isolates showed genetic similarity among different isolates obtained from different geographical regions barring few exceptions. Correlation between DNA patterns of R. solani isolates and their virulence was detected, but no correlation with anastomosis groups (AG).     

Development of a bioassay to assess resistance to Fusarium oxysporum (Schlecht.) in asparagus (Asparagus officinalis L.)

Fusarium oxysporum is one of the major pathogens causing root and crown rot in asparagus. Breeding of cultivars resistant to F. oxysporum would be the most efficient strategy for pathogen control. In this study, a bioassay was developed for screening seedling resistance. The non‐destructive bioassay comprises inoculation with a highly aggressive F. oxysporum isolate, incubation in a climate chamber and quantification of disease symptoms by a digital image analysing system and a PTA‐ELISA. This bioassay is simple to implement and demonstrated high reproducibility. Subsequently, it was used to determine the resistance behaviour of 16 asparagus genotypes to F. oxysporum. The asparagus cultivars revealed different levels of susceptibility, whereas the wild relative A. densiflorus was confirmed to be resistant.     

Effect of Placement and Sequence of Inoculation with Fusarium oxysporum on its Interaction with Meloidogyne arenaria on Subterranean Clover

The effect of the placement of inoculum of Fusarium oxysporum at two soil depths, and the sequences of inoculations with Meloidogyne arenaria and Fusarium oxysporum on root growth and development of root disease in Trifolium subterraneum L. (subterranean clover) were investigated. The timing of infection and the proximity of root tips of the host root system to infection by M. arenaria and F. oxysporum appeared to be the major determining factors of root growth and of disease development in plants exposed to the pathogens. Immediate contact of roots with F. oxysporum (where the fungus was placed at seed level of 10 mm depth) appeared to result in more severe effects on roots in the presence of the nematode than later infection by the fungus placed at 30 mm depth. The production of galls by the nematode and early infection by F. oxysporum at 10 mm depth resulted in a severe inhibition of root growth, particularly of the lateral roots. But no such growth inhibition was evident when F. oxysporum and M. arenaria were introduced together at the lower depth of 30 mm. The lowest density of M. arenaria inoculum was sufficient to cause severe root rot if F. oxysporum was present at the host seed level. With the fungus at 30 mm depth, however, the expression of root rot appeared to be influenced by the inoculum level of the nematode. In sequential inoculation with F. oxysporum or M. arenaria, the organism added 2 weeks later had little or no effect on root development. The first organism (M. arenaria or F. oxysporum) to infect the germinated seedlings was the main cause of root growth inhibition. The organism that came into contact with the roots 2 weeks later had little or no effect on the roots. Concurrent infection by F. oxysporum and M. arenaria resulted in less M. arenaria gall production on the tap root system than those added with the nematode alone or in advance of the fungus.     

Isolation and characterization of mutants of <Emphasis Type="Italic">Pseudomonas maltophila</Emphasis> PM-4 altered in chitinolytic activity and antagonistic activity against root rot pathogens of clusterbean (<Emphasis Type="Italic">Cyamopsis tetragonoloba</Emphasis>)

Pseudomonas maltophila PM-4, an antagonist of pathogenic fungi including Rhizoctonia bataticola, R. solani, Fusarium oxysporum and Sclerotinia sclerotiorum associated with root rot of clusterbean (Cyamopsis tetragonoloba) was mutagenized with Tn5. Hyperchitinase producing mutants showing large zone of colloidal chitin dissolution were identified on medium containing calcoflor dye as an indicator. A mutant P-48 producing 137% higher chitinase activity than the parent strain PM-4 was identified. Seed bacterization of clusterbean (Cyamopsis tetragonoloba) with P-48 controlled the root rot upto 40.8% in the presence of conglomerate of all the four fungal pathogens Rhizoctonia bataticola, R. solani, F. oxysporum and Sclerotinia sclerotiorum.     

First report of Plectosphaerella plurivora causing root rot disease in Panax notoginseng in China

Panax notoginseng is a highly valuable herb, but root rot disease severely impairs its development and decreases the yield and quality of roots. In this study, a fungal isolate (3A-2-2) was obtained from P. notoginseng seedlings with root rot symptoms and was identified as Plectosphaerella plurivora based on morphological characteristics and molecular analysis. The fungal isolate 3A-2-2 could cause root rot disease and be re-isolated, fulfilling Koch's postulates. This is the first study to report on root rot disease caused by P. plurivora on P. notoginseng in China.     

Control of pathogenic fungi on Panax notoginseng by volatile oils from the food ingredients Allium sativum and Foeniculum vulgare

To screen natural drugs with strong inhibitory effects against pathogenic fungi related to P. notoginseng, the antifungal activities of garlic and fennel EOs were studied by targeting P. notoginseng disease-associated fungi, and the possible action mechanisms of garlic and fennel EOs as plant fungicides were preliminarily discussed. At present, the antifungal mechanism of EOs has not been fully established. Therefore, understanding the antifungal mechanism of plant EOs is helpful to address P. notoginseng diseases continuous cropping disease-related obstacles and other agricultural cultivation problems. First, the Oxford cup method and chessboard were used to confirm that the EOs and oxamyl had a significant inhibitory effect on the growth of Fusarium oxysporum. F. oxysporum is the main pathogen causing root rot of P. notoginseng and the preliminary study on the antifungal mechanisms of the EOs against F. oxysporum showed that the inhibition of EOs mainly affects cell membrane permeability and cell processes and affects the enzyme activities of micro-organism, to achieve antifungal effects. Finally, an in vivo model verified that both two EOs could significantly inhibit the occurrence of root rot caused by F. oxysporum.     

Identification of Fusarium species causing basal rot of onion in East Azarbaijan province,Iran and evaluation of their virulence on onion bulbs and seedlings

One of the economically important diseases of onion is the basal rot caused by various Fusarium species. Identification of the pathogenic species prevalent in a region is indispensable for designing management strategies, especially to develop resistant cultivars. Eighty Fusarium isolates are obtained from red onion bulbs on infected fields of East Azarbaijan province. Inoculating the onion bulbs with 38 selective isolates indicated that 17 isolates were pathogenic on onion. According to the morphological and molecular characteristics, these isolates were identified as F. oxysporum, F. solani, F. proliferatum and F. redolens. This is the first report of F. redolens on onion in Iran. On the other hand, the virulence of each pathogenic isolate was evaluated on onion bulbs and seedlings. F. oxysporum which causes severe rot and damping-off was considered as a highly virulent species in both conditions. While, F. proliferatum was considered as the most destructive on onion bulbs. Rot ability of F. solani was not considerable, and only the 4S isolate caused pre- and post-emergence damping-off more than 50%. Finally, F. redolens with less pathogenicity on onion bulbs was identified as the most virulent isolate on onion seedlings, which was explanatory of its importance on farm.     

Biological control of Fusarium oxysporum f. sp. radicis-cucumerinum by some Trichoderma harzianum isolates

The purpose of this study was to investigate the effects of isolates T₂₂, T₉ and T₆ of Trichoderma harzianum on isolate F₄₂ of Fusarium oxysporum f. sp. radicis-cucumerinum. The effect of T. harzianum isolates on controlling disease was examined under greenhouse conditions. Results showed that these three isolates, respectively, had the high effect on inhibition of pathogen growth. In examining the severity of disease in the greenhouse, it was found that isolate T₂₂ had the greatest effect on controlling the pathogen. The results of volatile compounds showed that these isolates, respectively, were effective in reducing mycelial growth of isolate F₄₂. The highest peroxidase activity was observed on the fourth day in isolate T₆ and the highest phenylalanine ammonia lyase enzyme activity was observed on the fifth day in isolate T₂₂. Based on the results, isolate of T₂₂ showed the greatest effect on the induction of resistance against F₄₂ and may be a successful agent for biological control of root and stem rot of cucumber.     

Potential of endophytic Streptomyces spp. for biocontrol of Fusarium root rot disease and growth promotion of tomato seedlings

Sixteen endophytic actinobacteria isolated from roots of native plants were evaluated for their antagonistic potential against soil-borne phytopathogenic fungi. Among them, three strong antagonistic isolates were selected and characterised for in vitro plant-growth-promoting and biocontrol traits, including production of hydrogen cyanide, indole-3-acetic acid and siderophores, chitinase and β-1,3-glucanase activities, and inorganic phosphate solubilisation. In all trials, the strain Streptomyces sp. SNL2 revealed promising features. The selected actinobacteria were investigated for the biocontrol of Fusarium oxysporum f. sp. radicis lycopersici and for growth promotion of tomato (Solanum lycopersicum L. cv. Aïcha) seedlings in autoclaved and non-autoclaved soils. All seed-bacterisation treatments significantly reduced the root rot incidence compared to a positive control (with infested soil), and the isolate SNL2 exhibiting the highest protective activity. It reduced the disease incidence from 88.5% to 13.2%, whereas chemical seed treatment with Thiram® provided 14.6% disease incidence. Furthermore, isolate SNL2 resulted in significant increases in the dry weight, shoot and root length of seedlings. 16S rDNA sequence analysis showed that isolate SNL2 was related to Streptomyces asterosporus NRRL B-24328^T (99.52% of similarity). Its interesting biocontrol potential and growth enhancement of tomato seedlings open up attractive uses of the strain SNL2 in crop improvement.     

The effects of traits of Bacillus megaterium onseed and root colonization and their correlation withthe suppression of Rhizoctonia root rot of soybean

Bacillus megaterium strainB153-2-2 is a potential bacterial biocontrol agentagainst Rhizoctonia solani isolate 2B12(ISG-2B). To study the role of antagonism (Ant),chemotaxis (Che), motility (Mot), and sporulation(Spo) of the biocontrol agent during seed and rootcolonization and the correlation between rootcolonization and the suppression of soybean (Glycine max) root rot caused by R. solani,strain B153-2-2(Che⁺Mot⁺Ant⁺⁺Spo⁺⁺) and the sevenderived mutants with altered antagonism, chemotaxis,motility, and/or sporulation were used. The bacterialcells were introduced into soil separately either asa soybean seed coating or soil application. Two soilmixtures defined as coarse and fine soil were used. The bacterial cell chemotactic response to soybeanroot and seed exudates and antagonism to R.solani were significantly (p = 0.05) correlatedwith root and seed colonization in some but not alltreatments. The sporulation-defective mutants had lowcell populations immediately after application and,therefore, reduced root colonization. The differencesin root colonization diminished among the mutants andstrain B153-2-2 when R. solani was present inthe soil or, as seedlings grew older. Soybean seedlingroots grown in coarse soil had significantly greatercolonization by B153-2-2 or its mutants and a lowerdisease index than that in fine soil. There was asignificant positive correlation (r ² = 0.78)between root colonization by strain B153-2-2 or itsmutants and suppression of Rhizoctonia root rot.     

Characterization of Fusarium oxysporum f.sp. cepae from Onion in Turkey Based on Vegetative Compatibility and rDNA RFLP Analysis

Seventy‐five isolates of Fusarium oxysporum f.sp. cepae, the causal agent of basal plate rot on onion, were obtained from seven provinces of Turkey. The isolates were characterized by vegetative compatibility grouping (VCGs) and restriction fragment length polymorphism (RFLP) analysis of the nuclear ribosomal DNA intergenic spacer region (IGS). Forty‐eight vegetative compatibility groups were found, each containing a single isolate. Only one isolate formed strong heterokaryons with the reference isolates of VCG 0423. Five isolates were heterokaryon self‐incompatible. Restriction fragment analysis with six different enzymes revealed 13 IGS types among 75 F. oxysporum isolates from Turkey as well as 16 reference isolates from Colorado, USA. The majority of single‐member VCGs produced identical RFLP banding patterns with minor deviations, considerably different from those of the reference VCG isolates. These results suggested that isolates of F. oxysporum f.sp. cepae in Turkey derived from distinct clonal lineages and mutations at one or more vegetative compatibility loci restrict heterokaryon formation.     

Differential responses of molecular mechanisms and physiochemical characters in wild and cultivated soybeans against invasion by the pathogenic Fusarium oxysporum Schltdl

Cultivated soybean (Glycine max) was derived from the wild soybean (Glycine soja), which has genetic resources that can be critically important for improving plant stress resistance. However, little information is available pertaining to the molecular and physiochemical comparison between the cultivated and wild soybeans in response to the pathogenic Fusarium oxysporum Schltdl. In this study, we first used comparative phenotypic and paraffin section analyses to indicate that wild soybean is indeed more resistant to F. oxysporum than cultivated soybean. Genome‐wide RNA‐sequencing approach was then used to elucidate the genetic mechanisms underlying the differential physiological and biochemical responses of the cultivated soybean, and its relative, to F. oxysporum. A greater number of genes related to cell wall synthesis and hormone metabolism were significantly altered in wild soybean than in cultivated soybean under F. oxysporum infection. Accordingly, a higher accumulation of lignins was observed in wild soybean than cultivated soybean under F. oxysporum infection. Collectively, these results indicated that secondary metabolites and plant hormones may play a vital role in differentiating the response between cultivated and wild soybeans against the pathogen. These important findings may provide future direction to breeding programs to improve resistance to F. oxysporum in the elite soybean cultivars by taking advantage of the genetic resources within wild soybean germplasm.     

First Report of <i>Fusarium striatum</i> Causing Root Rot Disease of <i>Panax notoginseng</i> in Yunnan,China

Panax notoginseng is a traditional Chinese medicinal plant. Root rot of P. notoginseng is one of the most serious diseases affecting P. notoginseng growth and causes wilted leaves, fewer lateral roots and rotten roots. Root rot is a soil-borne disease, and mainly occurs from June to August in Yunnan Province when the temperatures are high and the air is humid. In this study, the endophytic fungal genus Fusarium isolate E-2018.1.22-#3.2 was obtained from a P. notoginseng embryo. Fusarium isolate E-2018.1.22-#3.2 was identified as Fusarium striatum based on morphological characteristics and molecular analysis. The fungus was found to have conidiophores and macroconidia, and its ITS, LSU and TEF-1α genes shared 100%, 99.2% and 99% identities with the homologous genes of Fusarium striatum, respectively. Isolate F. striatum E-2018.1.22-#3.2 can cause root rot symptoms, including black, soft roots, fewer lateral roots and leaf wilt, in 93% of the experimental P. notoginseng plants, and could be re-isolated, fulfilling Koch’s postulates. When the P. notoginseng plants were treated with the fungicide pyraclostrobin, isolate F. striatum E-2018.1.22-#3.2 was unable to cause root rot. We have therefore demonstrated that F. striatum E-2018.1.22-#3.2 is able to cause root rot disease in P. notoginseng. This is the first report of root rot disease caused by F. striatum on P. notoginseng in China.     

Integrated and biological control of gladiolus corm rot and wilt caused by Fusarium oxysporum f.sp. gladioli

An isolate of Trichoderma virens Miller, Giddens & Foster, carboxin and a combination of both were evaluated for the control of gladiolus corm rot and wilt caused by Fusarium oxysporum f.sp. gladioli in glasshouse and field experiments. All treatments significantly reduced disease incidence in both glasshouse and field conditions. T. virens gave control at least as good as carboxin in all experiments. Control was significantly improved in two field experiments by combining the biological and chemical treatments.     

Induction of defense-related proteins in tomato roots treated with Pseudomonas fluorescens Pf1 and Fusarium oxysporum f. sp. lycopersici

Pseudomonas fluorescens isolate Pf1 was found to protect tomato plants from wilt disease caused by Fusarium oxysporum f. sp. lycopersici. Induction of defense proteins and chemicals by P. fluorescens isolate Pf1 against challenge inoculation with F. oxysporum f. sp. lycopersici in tomato was studied. Phenolics were found to accumulate in bacterized tomato root tissues challenged with F. oxysporum f. sp. lycopersici at one day after pathogen challenge. The accumulation of phenolics reached maximum at the 5^th day after pathogen challenge. In pathogen-inoculated plants, the accumulation started at the 2^nd day and drastically decreased 4 days after the pathogen inoculation. Activities of phenylalanine ammonia-lyase (PAL), peroxidase (PO) and polyphenol oxidase (PPO) increased in bacterized tomato root tissues challenged with the pathogen at one day after pathogen challenge and activities of PAL and PO reached maximum at the 4^th day while activity of PPO reached maximum at the 5^th day after challenge inoculation. Isoform analysis revealed that a unique PPO1 isoform was induced and PO1 and PPO2 isoforms were expressed at higher levels in bacterized tomato root tissues challenge inoculated with the pathogen. Similarly, -1,3 glucanase, chitinase and thaumatin-like proteins (TLP) were induced to accumulate at higher levels at 3-5 days of challenge inoculation in bacterized plants. Western blot analysis showed that chitinase isoform Chi2 with a molecular weight of 46 kDa was newly induced due to P. fluorescens isolate Pf1 treatment challenged with the pathogen. TLP isoform with molecular weight of 33 kDa was induced not only in P. fluorescens isolate Pf1-treated root tissues challenged with the pathogen but also in roots treated with P. fluorescens isolate Pf1 alone and roots inoculated with the pathogen. These results suggest that induction of defense enzymes involved in phenylpropanoid pathway and accumulation of phenolics and PR-proteins might have contributed to restriction of invasion of F. oxysporum f. sp. lycopersici in tomato roots.     

Chemical control of root disease of Douglas–fir seedlings in relation to fungus and nematode populations

Seed treatment with thiram reduced post–emergence damping–off, while fumigating forest nursery soils with methyl bromide or DD improved Douglas-fir seedling emergence, shoot and root growth, and decreased the incidence of root disease. At an old site, where corky root develops, the benefits from these fumigants were associated with fewer (a) Xiphinema bakeri and (b) isolates of Cylindrocarpon radicicola. At a new site, decrease in Fusarium root rot and increase in shoot growth were related to reduction of populations of Paratylenchus and Pratylenchus, respectively. In unfumigated soils, Fusarium oxysporum was isolated from diseased and healthy roots.