Fusarium and Neocosmospora Species Associated with Rot of Cactaceae and Other Succulent Plants

Identification and screening of fungicides against Piper nigrum basal Fusarium wilt disease in Hainan, China

Fusarium wilt has occurred in the main Piper nigrum cultivation regions, which seriously affects the yield and quality of P. nigrum. To identify the pathogen of this disease, the diseased roots were collected from a demonstration base in Hainan Province. The pathogen was obtained by tissue isolation method and confirmed by pathogenicity test. Based on the morphological observation, sequence analyses of TEF1-α nuclear gene, Fusarium solani was identified as the pathogen causing P. nigrum Fusarium wilt and induced symptoms on inoculated plants, including chlorosis, necrotic spots, wilt, drying, and root rot. The experiments for the antifungal activity showed that all the 11 fungicides selected in this study showed certain inhibitory effects on the colony growth of F. solani, where 2% kasugamycin AS, 45% prochloraz EW, 25 g·L-1 fludioxonil SC and 430 g·L-1 tebuconazole SC exhibited relative higher inhibitory effects with EC50 as 0.065, 0.205, 0.395, and 0.483 mg·L-1 , respectively, and were selected to perform SEM analysis and test in seeds in vitro. The SEM analysis showed that kasugamycin, prochloraz, fludioxonil, and tebuconazole might have exerted their antifungal effect by damaging F. solani mycelia or microconidia. These preparations were applied as a seed coating of P. nigrum Reyin-1. The kasugamycin treatment was most effective in reducing the harmful impact of F. solani on the seed germination. These results presented herein provide useful guidance for the effective control of P. nigrum Fusarium wilt.

Molecular Variability of the Fusarium solani Species Complex Associated with Fusarium Wilt of Melon in Iran

Species of the Fusarium solani species complex (FSSC) are responsible for the Fusarium wilt disease of melon (Cucumis melo), a major disease of this crop in Iran. According to a recent taxonomic revision of Fusarium based primarily on multilocus phylogenetic analysis, Neocosmospora, a genus distinct from Fusarium sensu stricto, has been proposed to accommodate the FSSC. This study characterized 25 representative FSSC isolates from melon collected in 2009-2011 during a field survey carried out in five provinces of Iran. Pathogenicity assays showed the isolates were pathogenic on different varieties of melon and other cucurbits, including cucumber, watermelon, zucchini, pumpkin, and bottle gourd. Based on morphological characteristics and phylogenetic analysis of three genetic regions, including nrDNA internal transcribed spacer (ITS), 28S nrDNA large subunit (LSU) and translation elongation factor 1-alpha (tef1), Neocosmospora falciformis (syn. F. falciforme), N. keratoplastica (syn. F. keratoplasticum), N. pisi (syn. F. vanettenii), and Neocosmospora sp. were identified among the Iranian FSSC isolates. The N. falciformis isolates were the most numerous. This is the first report of N. pisi causing wilt and root rot disease in melon. Iranian FSSC isolates from different regions in the country shared the same multilocus haplotypes suggesting a long-distance dispersal of FSSC, probably through seeds.

Soybean continuous cropping affects yield by changing soil chemical properties and microbial community richness

In agroecosystems, different cropping patterns cause changes in soil physicochemical properties and thus in microbial communities, which in turn affect crop yields. In this study, the yields of soybean continuous cropping for 5 years (C5), 10 years (C10), and 20 years (C20) and of soybean-corn rotational cropping (R) treatments were determined, and samples of the tillage layer soil were collected. High-throughput sequencing technology was used to analyze the diversity and composition of the soil bacterial and fungal communities. The factors influencing microbial communities, along with the effects of these communities and those of soil chemical indexes on yield, were further evaluated. The results showed that the community richness index of bacteria was higher in C20 than in R and that of fungi was highest in C5. The differences in the bacterial and fungal communities diversity indexes were not significant among the different continuous cropping treatments, respectively. The soil microbial community composition of all continuous cropping treatments differed significantly from R. The dominant bacterial phylum was Actinobacteriota and the dominant fungal phylum was Ascomycota. The relative abundance of Fusarium did not differ significantly among the continuous cropping treatments, while that of the plant pathogen fungi Lectera sp., Plectosphaerella sp., and Volutella sp. increased with continuous cropping years. Soil pH, SOM, N, and TP had significant effects on both bacterial and fungal communities, and TK and C/N had highly significant effects on fungal communities. The yield of C5 was significantly lower than that of R, and the differences in yield between C10, C20, and R were not significant. TN, TP, and pH had significant effects on yield, and fungal community abundance had a greater negative effect on yield than bacterial community abundance.

Stilbocrea banihashemiana sp. nov. a New Fungal Pathogen Causing Stem Cankers and Twig Dieback of Fruit Trees

Stem cankers and twig dieback were the most serious disease of fig (Ficus carica) and loquat (Eriobotrya japonica) noticed in a survey of fruit tree orchards in the Fars Province, Iran. Isolates of Bionectriaceae were consistently recovered from symptomatic fig and loquat trees. Phylogenetic analyses of multiple nuclear loci, internal transcribed spacer regions (ITS) of rDNA, RNA polymerase II subunit 2 (rpb2), and translation elongation factor 1-α (tef1), combined with morphological observations, revealed that isolates could be referred to a still unknown taxon, which was formally described as Stilbocrea banihashemiana sp. nov. Phylogenetically, isolates from fig and loquat trees clustered in a well-supported monophyletic group within the Stilbocrea clade of Bionectriaceae, closely related to S. walteri. Stilbocrea banihashemiana sp. nov. was characterized by the lack of stilbella-like asexual structure in both natural substrates and pure cultures and produced two morphologically distinct types of conidia, globose and cylindrical, formed on short and long simple phialides. In pathogenicity tests, S. banihashemiana sp. nov. induced stem cankers in both fig and loquat, wood discoloration in fig and twig dieback in loquat. Pathogenicity tests also showed that the potential host range of this novel pathogen includes other economically relevant horticultural trees.

Co-infection of Fusarium aglaonematis sp. nov. and Fusarium elaeidis Causing Stem Rot in Aglaonema modestum in China

Aglaonema modestum (A. modestum) (Araceae) is an evergreen herbage, which is intensively grown as an ornamental plant in South China. A new disease was observed in A. modestum from 2020 to 2021 in Guangdong province, China. The disease symptoms associated with plants were initial leaf wilt, stem rot, and resulting plant death, leading to severe economic losses. In total, six Fusarium isolates were obtained from diseased plants. The putative pathogen was identified using both morphological characteristics and molecular phylogenetic analysis of calmodulin A (cmdA), RNA polymerase largest subunit 1 (rpb1), RNA polymerase II (rpb2), translation elongation factor-1α (tef1-α), and beta-tubulin (β-tubulin) sequences. Two Fusarium species were identified, namely, one new species, Fusarium aglaonematis (F. aglaonematis) belonging to Fusarium fujikuroi species complex. In addition, Fusarium elaeidis (F. elaeidis) belonging to the Fusarium oxysporum (F. oxysporum) species complex was also identified. Pathogenicity assays were conducted by inoculating each species into potted A. modestum plants and co-inoculating two species. The results showed that two Fusarium species could infect plants independently and can infect them together. Co-infection of these two species enhanced the disease severity of A. modestum. Compared to single inoculation of F. elaeidis, severity was higher and disease development was quicker when plants were only inoculated with F. aglaonematis. In addition, these two Fusarium species could infect Aglaonema plants without wounds, while inoculation with a physical injury increased disease severity. This is the first report of co-infection by F. aglaonematis and F. elaeidis causing stem rot on A. modestum worldwide. This study will be an addition to the knowledge of Fusarium diseases in ornamental plants. These results will provide a baseline to identify and control diseases associated with A. modestum.

Molecular and Pathogenic Characterization of Fusarium Species Associated with Corm Rot Disease in Saffron from China

Saffron (Crocus sativus L.) is a commercial spice crop well-known throughout the world, valued for culinary, colorant, and pharmaceutical purposes. In China, Fusarium nirenbergiae was detected as causative agent of saffron corm rot, the most pervasive disease for the first time in 2020. In the present study, 261 Fusarium-like isolates were recovered from 120 rotted corms in four saffron producing fields at Zhejiang, Shanghai, and Yunnan provinces, China, in 2021. A combination of morpho-cultural features and multilocus sequence analysis (MLSA) of the concatenated rpb2 (DNA-directed RNA polymerase II largest subunit) and tef1 (translation elongation factor 1-α) partial sequences showed that the isolates from saffron belong to Fusarium nirenbergiae as well as F. commune, and F. annulatum with isolation frequencies of 58.2%, 26.8%, and 14.9%, respectively. Notably, F. commune was more prevalent than F. annulatum in the collected samples. Pathogenicity tests confirmed that both species were pathogenic on saffron corm. This is the first report of F. annulatum and F. commune causing corm rot of saffron, globally. Outcomes of the current research demonstrate that Fusarium spp. associated with saffron corm rot are more diverse than previously reported. Furthermore, some plants were infected by two or more Fusarium species. Our findings broaden knowledge about Fusarium spp. that inflict corm rot and assist the development of control measures.