Narayan Chandra Paul

Prevalence, Characterization, and Mycotoxin Production Ability of Fusarium Species on Korean Adlay (Coix lacrymal-jobi L.) Seeds

Adlay seed samples were collected from three adlay growing regions (Yeoncheon, Hwasun, and Eumseong region) in Korea during 2012. Among all the samples collected, 400 seeds were tested for fungal occurrence by standard blotter and test tube agar methods and different taxonomic groups of fungal genera were detected. The most predominant fungal genera encountered were Fusarium, Phoma, Alternaria, Cladosporium, Curvularia, Cochliobolus and Leptosphaerulina. Fusarium species accounted for 45.6% of all species found; and, with phylogenetic analysis based on the combined sequences of two protein coding genes (EF-1α and β-tubulin), 10 Fusarium species were characterized namely, F. incarnatum (11.67%), F. kyushuense (10.33%), F. fujikuroi (8.67%), F. concentricum (6.00%), F. asiaticum (5.67%), F. graminearum (1.67%), F. miscanthi (0.67%), F. polyphialidicum (0.33%), F. armeniacum (0.33%), and F. thapsinum (0.33%). The Fusarium species were then examined for their morphological characteristics to confirm their identity. Morphological observations of the species correlated well with and confirmed their molecular identification. The ability of these isolates to produce the mycotoxins fumonisin (FUM) and zearalenone (ZEN) was tested by the ELISA quantitative analysis method. The result revealed that FUM was produced only by F. fujikuroi and that ZEN was produced by F. asiaticum and F. graminearum.

Fusarium root rot caused by Fusarium solani on sweet potato (Ipomoea batatas) in South Korea

Abstract Fusarium species are important post-harvest pathogens of sweet potato worldwide. A root rot disease was observed on sweet potato (Ipomoea batatas) at storage houses in different locations in South Korea during 2016–2017. The disease was characterized by circular lesions with dark and light brown concentric rings along with cavities in the inner part of the root. Seven isolates were recovered from diseased samples. Two representative isolates were cultured on potato dextrose agar and the morphology was studied. Macroconidia were cylindrical and slightly curved with blunt and rounded apical cells. The size of the macroconidia was 28.3 (15.0–44.3) × 5.8 (4.2–8.3) μm. The microconidia were fusiform to ovoid, variable in size and aseptate or rarely with single septa. Microconidial size varied from 9.2 (5.2–16.1) × 3.6 (2.6–4.5) μm. The fungal isolates were identified as Fusarium solani (Martius) Appel & Wollenweber emend. Snyder & Hansen on the basis of the morphological and cultural characteristics. The isolates were confirmed as F. solani on the basis of molecular identification by rDNA–ITS and translation elongation factor (EF 1-α) gene sequence analysis. The pathogenicity of the organism was confirmed by fulfilling Koch’s postulates. To our knowledge, this is the first report of F. solani root rot of sweet potato in South Korea.

Phylogenetic Placement and Morphological Characterization of Sclerotium rolfsii (Teleomorph: Athelia rolfsii) Associated with Blight Disease of Ipomoea batatas in Korea

Abstract In this study, we aimed to characterize fungal samples from necrotic lesions on collar regions observed in different sweetpotato growing regions during 2015 and 2016 in Korea. Sclerotia appeared on the root zone soil surface, and white dense mycelia were observed. At the later stages of infection, mother roots quickly rotted, and large areas of the plants were destroyed. The disease occurrence was monitored at 45 and 84 farms, and 11.8% and 6.8% of the land areas were found to be infected in 2015 and 2016, respectively. Fungi were isolated from disease samples, and 36 strains were preserved. Based on the cultural and morphological characteristics of colonies, the isolates resembled the reference strain of Sclerotium rolfsii. Representative strains were identified as S. rolfsii (teleomorph: Athelia rolfsii) based on phylogenetic analysis of the internal transcribed spacer and large subunit genes along with morphological observations. To test the pathogenicity, sweetpotato storage roots were inoculated with different S. rolfsii strains. ‘Yulmi’ variety displayed the highest disease incidence, whereas ‘Pungwonmi’ resulted in the least. These findings suggested that morphological characteristics and molecular phylogenetic analysis were useful for identification of S. rolfsii.

First report of powdery mildew caused by Podosphaera sp. on Cynanchum auriculatum

Powdery mildew symptoms were observed on the upper surface of leaves of Cynanchum auriculatum in Eumseong, Korea in October 2015. Microscopic observations and molecular characteristics determined this fungus as Podosphaera sp., which is reported for the first time on Cynanchum auriculatum.