Histopathology and quantification of green fluorescent protein-tagged Fusarium oxysporum f. sp. luffae isolate in resistant and susceptible Luffa germplasm

Fusarium oxysporum f. sp. luffae (Folu) is a severe plant pathogen that causes vascular wilt and root rot in Luffa plants worldwide. A green fluorescent protein (GFP)-tagged isolate of Folu (Fomh16-GFP) was utilized to investigate the infection progress and colonization of Fomh16-GFP in resistant (LA140) and susceptible (LA100) Luffa genotypes. Seven days post-inoculation (dpi), it was observed that Fomh16-GFP had successfully invaded and colonized the vascular bundle of all LA100 parts, including the roots, hypocotyl, and stem. Pathogen colonization continued to increase over time, leading to the complete wilting of plants by 14-17 dpi. In LA140, the Fomh16-GFP isolate colonized the roots and hypocotyl vascular system at 7 dpi. Nevertheless, this colonization was restricted in the hypocotyl and decreased significantly, and no fungal growth was detected in the vascular system at 21 dpi. Thus, the resistant genotype might trigger a robust defense mechanism. In addition, while the pathogen was present in LA140, the inoculated plants did not exhibit any symptoms until 28 dpi. Quantitative PCR was utilized to measure the Fomh16-GFP biomass in various parts of LA100 and LA140 at different time points. The findings indicated a positive correlation between the quantity of Fomh16-GFP DNA and disease development in LA100. Alternatively, a high amount of Fomh16-GFP DNA was identified in the roots of LA140. Nonetheless, no significant correlations were found between DNA amount and disease progression in LA140. Aqueous extracts from LA140 significantly reduced Fomh16-GFP spore germination, while no significant reduction was detected using LA100 extracts.IMPORTANCEFusarium wilt of Luffa, caused by Fusarium oxysporum f. sp. luffae (Folu), causes great losses in Luffa plants worldwide. This study used a green fluorescent protein (GFP)-tagged isolate of Folu (Fomh16-GFP) to investigate the infection progress and colonization dynamics of Fomh16-GFP in the resistant and susceptible Luffa genotypes, which could be important in understanding the resistance mechanism of Folu in Luffa plants. In addition, our work highlights the correlations between DNA amount and disease progression in resistant plants using real-time PCR. We observed a positive correlation between the quantity of Fomh16-GFP DNA and disease progression in LA100, while no significant correlation was found in LA140. These results could be valuable to further investigate the resistance mechanism of Luffa genotypes against Folu. Gaining a better understanding of the interaction between Folu and Luffa plants is crucial for effectively managing Fusarium wilt and enhancing resistance in Luffa rootstock and its varieties.

Species diversity and major host/substrate associations of the genus Akanthomyces (Hypocreales, Cordycipitaceae)

Akanthomyces, a group of fungi with rich morphological and ecological diversity in Cordycipitaceae (Ascomycota, Hypocreales), has a wide distribution amongst diverse habitats. By surveying arthropod-pathogenic fungi in China and Southeast Asia over the last six years, nine Akanthomyces spp. were found and identified. Five of these were shown to represent four known species and an undetermined species of Akanthomyces. Four of these were new species and they were named A.kunmingensis and A.subaraneicola from China, A.laosensis from Laos and A.pseudonoctuidarum from Thailand. The new species were described and illustrated according to the morphological characteristics and molecular data. Akanthomycesaraneogenus, which was isolated from spiders from different regions in China, Thailand and Vietnam, was described as a newly-recorded species from Thailand and Vietnam. The phylogenetic positions of the nine species were evaluated, based on phylogenetic inferences according to five loci, namely, ITS, nrLSU, TEF, RPB1 and RPB2. In this study, we reviewed the research progress achieved for Akanthomyces regarding its taxonomy, species diversity, geographic distribution and major host/substrate associations. The morphological characteristics of 35 species in Akanthomyces, including four novel species and 31 known taxa, were also compared.

Phylogeny and species delimitations in the economically, medically, and ecologically important genus Samsoniella (Cordycipitaceae, Hypocreales)

Samsoniella is a ubiquitous genus of cosmopolitan arthropod-pathogenic fungi in the family Cordycipitaceae. The fungi have economic, medicinal, and ecological importance. Prior taxonomic studies of these fungi relied predominantly on phylogenetic inferences from five loci, namely, the nuclear ribosomal small and large subunits (nr SSU and nr LSU), the 3' portion of translation elongation factor 1 alpha (3P_TEF), and RNA polymerase II subunits 1 and 2 (RPB1 and RPB2). Despite many new species being described, not all of the recognized species inside this group formed well-supported clades. Thus, the search for new markers appropriate for molecular phylogenetic analysis of Samsoniella remains a challenging problem. In our study, we selected the internal transcribed spacer regions of the rDNA (ITS rDNA) and seven gene regions, namely, 3P_TEF, the 5' portion of translation elongation factor 1 alpha (5P_TEF), RPB1, RPB2, γ-actin (ACT), β-tubulin (TUB), and a gene encoding a minichromosome maintenance protein (MCM7), as candidate markers for species identification. Genetic divergence comparisons showed that the ITS, RPB2, ACT, and TUB sequences provided little valuable information with which to separate Samsoniella spp. In contrast, sequence data for 3P_TEF, 5P_TEF, RPB1, and MCM7 provided good resolution of Samsoniella species. The phylogenetic tree inferred from combined data (5P_TEF + 3P_TEF + RPB1 + MCM7) showed well-supported clades for Samsoniella and allowed for the delimitation of 26 species in this genus. The other two species (S.formicae and S.lepidopterorum) were not evaluated, as they had abundant missing data.

Phylogeny and systematics of the genus Clonostachys

Introduction

Clonostachys, a genus with rich morphological and ecological diversity in Bionectriaceae, has a wide distribution among diverse habitats.

Methods and Results

In the present study, a phylogenetic framework is reconstructed for the family Bionectriaceae focusing on Clonostachys through increased taxon-sampling using the nrLSU sequence. Through surveying Clonostachys in China, Vietnam, and Thailand over the past 3 years, seven Clonostachys spp. were found and identified. Two new species, C. chuyangsinensis and C. kunmingensis, are described and illustrated based on morphological characteristics and molecular data. The phylogenetic positions of the seven species were evaluated based on four genomic loci (ITS, nrLSU, TUB2, and TEF1).

Discussion

Moreover, the genetic divergence comparisons of Clonostachys species for three markers (ITS, TUB2, and TEF1) are also provided. The results indicated that the TEF1 sequence data provided the best resolution for distinguishing species of Clonostachys, followed by sequence data for the TUB2 and ITS regions.

Sensitivity of Colletotrichum gloeosporioides species complex (CGSC) isolated from strawberry in Taiwan to benzimidazole and strobilurin

Colletotrichum gloeosporioides species complex (CGSC) is the major pathogen causing strawberry anthracnose in Taiwan. Benzimidazoles and strobilurins are common fungicides used to control strawberry anthracnose. A total of 108 CGSC isolates were collected from five major strawberry-producing areas in Taiwan. The half-maximal effective concentration (EC₅₀) values of most CGSC isolates for benomyl (59 isolates), carbendazim (70 isolates), and thiabendazole (63 isolates) were higher than 500 µg a.i./mL. Strobilurin tests showed that the EC₅₀ values of most CGSC isolates for azoxystrobin (66 isolates), kresoxim-methyl (42 isolates), and trifloxystrobin (56 isolates) were higher than 500 µg a.i./mL. However, most CGSC isolates were sensitive to pyraclostrobin at 100 µg a.i./mL. Fungicide tests indicated that CGSC isolates show multi-resistance to benzimidazoles and strobilurins. Benzimidazole-resistant isolates were associated with a point mutation in codon 198 of the β-tubulin gene, and strobilurin-resistant isolates did not correspond with mutation in the cyt b gene or alternative oxidase activity.

Colonization of human opportunistic Fusarium oxysporum (HOFo) isolates in tomato and cucumber tissues assessed by a specific molecular marker

Fusarium oxysporum is a large complex cosmopolitan species composed of plant pathogens, human opportunistic pathogens, and nonpathogenic isolates. Many plant pathogenic strains are known based on host plant specificity and the large number of plant species attacked. F. oxysporum is an opportunistic pathogen in humans with a compromised immune system. The objectives of this study were: (1) to develop a specific marker to detect human opportunistic F. oxysporum (HOFo) isolates; (2) to determine whether or not HOFo isolates can colonize and cause disease symptoms in plants; and (3) to assess Taiwan isolates sensitivity to two agro-fungicides. The primer pair, Primer 5/ST33-R, specifically amplifying Taiwan and international reference HOFo isolates was developed and used to detect and assess the distribution of a Taiwan isolate in inoculated tomato plants and tomato and cucumber fruit. Taiwan HOFo isolate MCC2074 was shown to colonize tomato roots, hypocotyls, and cotyledons, but did not show any visible symptoms. Four days after surface inoculation of tomato and cucumber fruit with the same isolate, MCC2074 was detected in the pericarp and locular cavities of both tomato and cucumber fruit and in columella of tomato fruit. Three Taiwan HOFo isolates were found to be moderately sensitive to azoxystrobin and highly sensitive to difenconazole.