A Novel Disease of Mung Bean, Phytophthora Stem Rot Caused by a New Forma Specialis of Phytophthora vignae

An emerging soil-borne disease resembling Phytophthora stem rot was observed on mung bean plants grown in Anhui, China. To identify the causal agent, diseased plants and soil samples from 13 fields were collected to isolate the pathogen. Twenty-two Phytophthora isolates were recovered from the samples and conducted for detailed identification. Based on morphological and molecular characterizations, all the isolates were consistently identified as Phytophthora vignae. Phylogenetic analysis using eight nuclear loci sequences of the internal transcribed spacer (ITS) region, rRNA gene large subunit (LSU), a partial sequence of the beta-tubulin (β-tubulin) gene, the translation elongation factor 1 alpha (EF1-α), the 60S ribosomal protein L10 (60SL10), enolase (Enl) gene, the heat shock protein 90 (HSP90), and the triose phosphate isomerase/glyceraldehyde-3-phosphate dehydrogenase (TigA) and a mitochondrial locus cytochrome c oxidase subunit I (cox1) revealed that the mung bean isolates group in the same clade as P. vignae and its two formae speciales, P. vignae f. sp. adzukicola and P. vignae f. sp. vignae. A host specificity test showed that the mung bean isolates of P. vignae are pathogenic towards mung bean with a much stronger virulence and towards adzuki bean with a relatively weak virulence, but non-pathogenic to the other tested legume crops, soybean, cowpea, pea, common bean, faba bean, and chickpea. The host range of mung bean isolates significantly differs from that of the P. vignae f. sp. adzukicola and f. sp. vignae, based on our results and the previous studies. Thus, the pathogen causing Phytophthora stem rot of mung bean is proposed as a new forma specialis of P. vignae, designated as P. vignae f. sp. mungcola.

Development of specific primers for Fusarium oxysporum causing damping off of Lilium formolongi

Primers specific for the hypothetical forma specialis of Fusarium oxysporum were designed to amplify DNA from this pathogenic fungus that infects plants including lilies. The F. oxysporum sequence between the transposal elements han and hop was used for primer design. Three primer pairs designed from this region were confirmed as specific for 24 isolates of F. oxysporum pathogenic to lilies, except for one pathogenic isolates as extraordinary. No amplification was observed from F. oxysporum non-pathogenic to lily, from 12 forma specialis, and 14 fungi and oomycetes concerned with Liliaceae plants. We propose that specific primers designed from this region will be useful to detect isolates of F. oxysporum that are pathogenic to lilies.

Identifikasi Infraspesifik Fusarium oxysporum asal Subtrat Nonpisang dan Kemampuan Pindah Inangnya ke Tanaman Pisang

Infra-specific Identification of Fusarium oxysporum from Nonbanana Substrates and Its Ability to Move Hosts to Banana PlantsFusarium oxysporum has various life style, i.e. saprobe, endophyte and pathogen. Plant pathogenic F. oxysporum are divided into many forma specialis (f. sp.) depending on the host, for instance F. oxysporum f. sp. cubense (Foc), a causal agent of Panama disease of banana. The study aimed to determine the infraspecific identity of F. oxysporum from non-banana host and evaluate its ability to jump banana plants. Infraspecific identity was determined through a molecular approach using 3 specific primers to recognize TR4 race (TR4 F/R, TR4 F/R1, and FocSc-1/ FocSc-2), while the host’s transfer ability was tested on 2 banana cultivars namely cv. Ambon and Tanduk. Thirteen strain studied i.e IPBCC 88,012, IPBCC 07,528, IPBCC 07,561, IPBCC 08,562, IPBCC 08,568, IPBCC 10.674, IPBCC 14.1236, IPBCC 14.1237, IPBCC 14.1238 and IPBCC 14.1239 were TR4 Foc; IPBCC 07,338 and IPBCC 14.1242 are race Foc 4. The pathogenicity test of Foc IPBCC 88,012, 07,328, 08,561, 10,674 and 14.1236 derived from cucumbers, soil, agarwood sapwood, insect nests and quinine tree endophytes showed that these strains were able to move to banana plant. This shows that Foc may not host-specific and the infaspecific term forma specialis is therefore debatable.

Current Status of Fusarium oxysporum Formae Speciales and Races

The Fusarium oxysporum species complex includes both plant pathogenic and nonpathogenic strains, which are commonly found in soils. F. oxysporum has received considerable attention from plant pathologists for more than a century owing to its broad host range and the economic losses it causes. The narrow host specificity of pathogenic strains has led to the concept of formae speciales, each forma specialis grouping strains with the same host range. Initially restricted to one plant species, this host range was later found to be broader for many formae speciales. In addition, races were identified in some formae speciales, generally with cultivar-level specialization. In 1981, Armstrong and Armstrong listed 79 F. oxysporum formae speciales and mentioned races in 16 of them. Since then, the known host range of F. oxysporum has considerably increased, and many new formae speciales and races have been identified. We carried out a comprehensive search of the literature to propose this review of F. oxysporum formae speciales and races. We recorded 106 well-characterized formae speciales, together with 37 insufficiently documented ones, and updated knowledge on races and host ranges. We also recorded 58 plant species/genera susceptible to F. oxysporum but for which a forma specialis has not been characterized yet. This review raises issues regarding the nomenclature and the description of F. oxysporum formae speciales and races.

Reaction of pea selections to Fusarium oxysporum f.sp. pisi (races 1, 2, 5, 6) and Fusarium solani

Forma specialis (f.sp.) pisi of Fusarium oxysporum infestates pea but on other crop does not cause. Physiological races of this fungus (races 1, 2, 3 and 6) are tested on differentiation selections of pea. In the mixture with Fusarium solani there was better differentiated the reaction of single races. Own method is based on the artificial infection of the pea with the mixture of conidia and mycelial fragments of the race of Fusarium oxysporum f.sp. pisi and Fusarium solani. The roots of germinating pea are partially shortened on the top and poured with the suspension of fungi. After the germinating the infected pea is placed into Perlit (the substance for the cultivation). The pea was watered after that. During 3 years of our work we tested namely many new selections from the breeding station in Lužany. It seems that some of them should be used for new selection of realy resistant varieties. In the year 1999 there were new selection relatively resistant: 595/32, 682/37, 238/847, in the year 2000 no resistant selections were gained and in the year 2001 there were like resistant evaluated these selections: 633/1409 and 1456/1919.

Fusarium oxysporumf. sp.mori, a New Forma Specialis Causing Fusarium Wilt of Blackberry

Fusarium oxysporum has recently been identified as the cause of a wilt disease affecting blackberry in California and Mexico. Thirty-six isolates of F. oxysporum obtained from symptomatic blackberry plants in California and Mexico were comprised of nine distinct somatic compatibility groups (SCGs). Phylogenetic analysis of a concatenated data set, consisting of sequences of the translation elongation factor 1-α and β-tubulin genes and the intergenic spacer of the ribosomal DNA, identified nine three-locus sequence types, each of which corresponded to an SCG. Six SCGs were present only in California, two only in Mexico, and one in both California and Mexico. An isolate associated with the most common SCG in California was tested for pathogenicity on blueberry, raspberry, strawberry, and lettuce. All blueberry, raspberry, and lettuce plants that were inoculated remained healthy, but two of the five strawberry cultivars tested developed symptoms. The three strawberry cultivars that were resistant to the blackberry pathogen were also resistant to F. oxysporum f. sp. fragariae, the cause of Fusarium wilt of strawberry. We propose to designate strains of F. oxysporum that are pathogenic to blackberry as Fusarium oxysporum f. sp. mori forma specialis nov.

Use of Comparative Genomics-Based Markers for Discrimination of Host Specificity in Fusarium oxysporum

ABSTRACTThe polyphyletic nature of manyformae specialesofFusarium oxysporumprevents molecular identification of newly encountered strains based on conserved, vertically inherited genes. Alternative molecular detection methods that could replace labor- and time-intensive disease assays are therefore highly desired. Effectors are functional elements in the pathogen-host interaction and have been found to show very limited sequence diversity between strains of the sameforma specialis, which makes them potential markers for host-specific pathogenicity. We therefore compared candidate effector genes extracted from 60 existing and 22 newly generated genome assemblies, specifically targeting strains affecting cucurbit plant species. Based on these candidate effector genes, a total of 18 PCR primer pairs were designed to discriminate between each of the seven Cucurbitaceae-affectingformae speciales. When tested on a collection of strains encompassing different clonal lineages of theseformae speciales, nonpathogenic strains, and strains of otherformae speciales, they allowed clear recognition of the host range of each evaluated strain. WithinFusarium oxysporumf. sp.melonismore genetic variability exists than anticipated, resulting in threeF. oxysporumf. sp.melonismarker patterns that partially overlapped with the cucurbit-infectingFusarium oxysporumf. sp.cucumerinum,Fusarium oxysporumf. sp.niveum,Fusarium oxysporumf. sp.momordicae, and/orFusarium oxysporumf. sp.lagenariae. ForF. oxysporumf. sp.niveum, a multiplex TaqMan assay was evaluated and was shown to allow quantitative and specific detection of template DNA quantities as low as 2.5 pg. These results provide ready-to-use marker sequences for the mentionedF. oxysporumpathogens. Additionally, the method can be applied to find markers distinguishing other host-specific forms ofF. oxysporum.IMPORTANCEPathogenic strains ofFusarium oxysporumare differentiated intoformae specialesbased on their host range, which is normally restricted to only one or a few plant species. However, horizontal gene transfer between strains in the species complex has resulted in a polyphyletic origin of host specificity in many of theseformae speciales. This hinders accurate and rapid pathogen detection through molecular methods. In our research, we compared the genomes of 88 strains ofF. oxysporumwith each other, specifically targeting virulence-related genes that are typically highly similar within eachforma specialis. Using this approach, we identified marker sequences that allow the discrimination ofF. oxysporumstrains affecting various cucurbit plant species through different PCR-based methods.