Concept: Fusarium oxysporum
Banana (Musa spp.) is a staple food for more than 400 million people. Over 40% of world production and virtually all the export trade is based on Cavendish banana. However, Cavendish banana is under threat from a virulent fungus, Fusarium oxysporum f. sp. cubense tropical race 4 (TR4) for which no acceptable resistant replacement has been identified. Here we report the identification of transgenic Cavendish with resistance to TR4. In our 3-year field trial, two lines of transgenic Cavendish, one transformed with RGA2, a gene isolated from a TR4-resistant diploid banana, and the other with a nematode-derived gene, Ced9, remain disease free. Transgene expression in the RGA2 lines is strongly correlated with resistance. Endogenous RGA2 homologs are also present in Cavendish but are expressed tenfold lower than that in our most resistant transgenic line. The expression of these homologs can potentially be elevated through gene editing, to provide non-transgenic resistance.
Antimicrobial peptides are a potent group of defense active molecules that have been utilized in developing resistance against a multitude of plant pathogens. Floral defensins constitute a group of cysteine-rich peptides showing potent growth inhibition of pathogenic filamentous fungi especially Fusarium oxysporum in vitro. Full length genes coding for two Petunia floral defensins, PhDef1 and PhDef2 having unique C-terminal 31 and 27 amino acid long predicted prodomains, were overexpressed in transgenic banana plants using embryogenic cells as explants for Agrobacterium-mediated genetic transformation. High level constitutive expression of these defensins in elite banana cv. Rasthali led to significant resistance against infection of Fusarium oxysporum f. sp. cubense as shown by in vitro and ex vivo bioassay studies. Transgenic banana lines expressing either of the two defensins were clearly less chlorotic and had significantly less infestation and discoloration in the vital corm region of the plant as compared to untransformed controls. Transgenic banana plants expressing high level of full-length PhDef1 and PhDef2 were phenotypically normal and no stunting was observed. In conclusion, our results suggest that high-level constitutive expression of floral defensins having distinctive prodomains is an efficient strategy for development of fungal resistance in economically important fruit crops like banana.
Autotoxicity of cucumber root exudates or decaying residues may be the cause of the soil sickness of cucumber. However, how autotoxins affect soil microbial communities is not yet fully understood.
Arbuscular mycorrhizal fungi (AMF) and their bioprotective aspects are of great interest in the context of sustainable agriculture. Combining the benefits of AMF with the utilisation of plant species diversity shows great promise for the management of plant diseases in environmentally compatible agriculture. In the present study, AMF were tested against Fusarium oxysporum f. sp. lycopersici with tomato intercropped with either leek, cucumber, basil, fennel or tomato itself. Arbuscular mycorrhizal (AM) root colonisation of tomato was clearly affected by its intercropping partners. Tomato intercropped with leek showed even a 20 % higher AM colonisation rate than tomato intercropped with tomato. Positive effects of AMF expressed as an increase of tomato biomass compared to the untreated control treatment could be observed in root as well as in shoot weights. A compensation of negative effects of F. oxysporum f. sp. lycopersici on tomato biomass by AMF was observed in the tomato/leek combination. The intercropping partners leek, cucumber, basil and tomato had no effect on F. oxysporum f. sp. lycopersici disease incidence or disease severity indicating no allelopathic suppression; however, tomato co-cultivated with tomato clearly showed a negative effect on one plant/pot with regard to biomass and disease severity of F. oxysporum f. sp. lycopersici. Nonetheless, bioprotective effects of AMF resulting in the decrease of F. oxysporum f. sp. lycopersici disease severity were evident in treatments with AMF and F. oxysporum f. sp. lycopersici co-inoculation. However, these bioprotective effects depended on the intercropping partner since these effects were only observed in the tomato/leek and tomato/basil combination and for the better developed plant of tomato/tomato. In conclusion, the effects of the intercropping partner on AMF colonisation of tomato are of great interest for crop plant communities and for the influences on each other. The outcome of the bioprotective effects of AMF resulting in the decrease on F. oxysporum f. sp. lycopersici disease severity and/or compensation of plant biomass does not depend on the degree of AM colonisation but more on the intercropping partner.
Genetic analysis and chromosome mapping of resistance to Fusarium oxysporum f. sp. niveum (FON) race 1 and race 2 in watermelon (Citrullus lanatus L.)
- Molecular breeding : new strategies in plant improvement
- Published about 5 years ago
Fusarium wilt (FW) caused by Fusarium oxysporum f. sp. niveum (FON) is the major soilborne disease of watermelon (Citrullus lanatus L.). The development and deployment of resistant cultivars is generally considered to be an effective approach to control FW. In this study, an F8 population consisting of 103 recombinant inbred lines derived from a cross between the cultivar 97103 and a wild accession PI 296341-FR was used for FON race 1 and race 2 fungal inoculations. One major QTL on chromosome 1 for FON race 1 resistance was detected with a logarithm of odds of 13.2 and explained phenotypic variation R (2) = 48.1 %; two QTLs of FON race 2 resistance on chromosomes 9 and 10 were discovered based on the high-density integrated genetic map we constructed. The nearest molecular marker should be useful for marker-assisted selection of FON race 1 and race 2 resistance. One receptor kinase, one glucan endo-1,3-β-glucosidase precursors and three acidic chitinase located in the FON-1 QTL genomic region. In Qfon2.1 QTL region, one lipoxygenase gene, five receptor-like kinases and four glutathione S-transferase genes are discovered. One arginine biosynthesis bifunctional protein, two receptor kinase proteins and one lipid-transfer protein located in Qfon2.2 QTL region. Based on SNP analysis by using 20 re-sequenced accessions of watermelon and 231-plant F2 population generated from Black Diamond × Calhoun Grey, we developed a SNP marker Chr1SNP_502124 for FON-1 detection.
Streptomyces griseus S4-7 was originally isolated from the strawberry rhizosphere as a microbial agent responsible for Fusarium wilt suppressive soils. S. griseus S4-7 shows specific and pronounced antifungal activity against Fusarium oxysporum f. sp. fragariae. In the Streptomyces genus, the whi transcription factors are regulators of sporulation, cell differentiation, septation, and secondary metabolites production. wblE2 function as a regulator has emerged as a new group in whi transcription factors. In this study, we reveal the involvement of the wblE2 transcription factor in the plant-protection by S. griseus S4-7. We generated ΔwblE, ΔwblE2, ΔwhiH, and ΔwhmD gene knock-out mutants, which showed less antifungal activity both in vitro and in planta. Among the mutants, wblE2 mutant failed to protect the strawberry against the Fusarium wilt pathogen. Transcriptome analyses revealed major differences in the regulation of phenylalanine metabolism, polyketide and siderophore biosynthesis between the S4-7 and the wblE2 mutant. The results contribute to our understanding of the role of streptomycetes wblE2 genes in a natural disease suppressing system.
Banana (Musa spp.) is one of the world’s most important fruits. In 2011, 145 million metric tons worth an estimated $44 billion were produced in over 130 countries. Fusarium wilt (aka Panama disease) is one of the most destructive diseases of this crop. It devastated the ‘Gros Michel’-based export trades before the mid-1900s, and threatens the Cavendish cultivars that were used to replacement it; in total, the latter cultivars are now responsible for ca 45% of all production. An overview of the disease and its causal agent, Fusarium oxysporum f. sp. cubense (Foc), is presented below. Despite a substantial positive literature on biological, chemical or cultural measures, management is largely restricted to excluding Foc from noninfested areas and using resistant cultivars where the pathogen has established. Resistance to Fusarium wilt is poor in several breeding targets, including important dessert and cooking cultivars. Better resistance to this and other diseases is needed. The history and impact of Fusarium wilt is summarized with an emphasis on tropical race 4 (TR4), a Cavendish-killing variant of the pathogen that has spread dramatically in the Eastern Hemisphere.
The primary mechanism underlying antagonism among microorganisms is the production of antagonistic substances called antibiotics that inhibit the growth of pathogens. In this study, the antagonistic substances produced by the Bacillus amyloliquefaciens strain NJN-6 that had antifungal activity against Fusarium oxysporum were extracted and identified. The active antifungal substance was extracted from dried leavening with ultrasound-assisted extraction (UAE), using n -butanol as the extractant. HPLC/ESI-MS was performed to investigate the components of the extracts. The results of the study showed that the antimicrobial substances consisted of three homologues of the iturin A family with molecular weights of 1043, 1057 and 1071 Da and of two homologues of the fengycin family with molecular weights of 1477 and 1491 Da. The effects of ultrasonic treatment time, extraction time and extractant volume, three major methodological parameters, were also studied to determine the optimal conditions for extraction. Compared with traditional extraction techniques, UAE is a simple, cheap and environmentally friendly method that represents a new option for the isolation and identification of lipopeptides and other active compounds. These antifungal substances extracted and identified from Bacillus amyloliquefaciens NJN-6 will help us to understand its biocontrol mechanism against Fusarium oxysporum. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).
Host-specific forms of Fusarium oxysporum infect the roots of numerous plant species. I present a novel application of familiar methodology to visualize and quantify F. oxysporum in roots. Infection in the roots of Arabidopsis thaliana, tomato, and cotton was detected with colorimetric reagents that are substrates for Fusarium spp.-derived arabinofuranosidase and N-acetyl-glucosaminidase activities and without the need for genetic modification of either plant host or fungal pathogen. Similar patterns of blue precipitation were produced by treatment with 5-bromo-4-chloro-3-indoxyl-α-l-arabinofuranoside and 5-bromo-4-chloro-3-indoxyl-2-acetamido-2-deoxy-β-d-glucopyranoside, and these patterns were consistent with prior histological descriptions of F. oxysporum in roots. Infection was quantified in roots of wild-type and mutant Arabidopsis using 4-nitrophenyl-α-l-arabinofuranoside. In keeping with an expectation that disease severity above ground is correlated with F. oxysporum infection below ground, elevated levels of arabinofuranosidase activity were measured in the roots of susceptible agb1 and rfo1 while a reduced level was detected in the resistant eir1. In contrast, disease severity and F. oxysporum infection were uncoupled in tir3. The distribution of staining patterns in roots suggests that AGB1 and RFO1 restrict colonization of the vascular cylinder by F. oxysporum whereas EIR1 promotes colonization of root apices.
Plant roots react to pathogen attack by the activation of general and systemic resistance, including the lignification of cell walls and increased release of phenolic compounds in root exudate. Some fungi have the capacity to degrade lignin using ligninolytic extracellular peroxidases and laccases. Aromatic lignin breakdown products are further catabolized via the β-ketoadipate pathway. In this study, we investigated the role of 3-carboxy-cis,cis-muconate lactonizing enzyme (CMLE), an enzyme of the β-ketoadipate pathway, in the pathogenicity of Fusarium oxysporum f. sp. lycopersici towards its host, tomato. As expected, the cmle deletion mutant cannot catabolize phenolic compounds known to be degraded via the β-ketoadipate pathway. In addition, the mutant is impaired in root invasion and is nonpathogenic, even though it shows normal superficial root colonization. We hypothesize that the β-ketoadipate pathway in plant-pathogenic, soil-borne fungi is necessary to degrade phenolic compounds in root exudate and/or inside roots in order to establish disease.