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Chlorine dioxide (ClO2) has been widely used as an effective disinfectant to control fungal contamination during postharvest crop storage. In this study, Fusarium oxysporum f. sp. batatas SP-f6 from the black rot symptom of sweetpotato was isolated and identified using phylogenetic analysis of elongation factor 1-α gene; we further examined the in vitro and in vivo inhibitory activities of ClO2 gas against the fungus. In the in vitro medium tests, fungal population was significantly inhibited upon increasing the concentration and exposure time. In in vivo tests, spore suspensions were drop-inoculated onto sweetpotato slices, followed by treatment using various ClO2 concentrations and treatment times to assess fungus-induced disease development in the slices. Lesion diameters decreased at the tested ClO2 concentrations over time. When sweetpotato roots were dip-inoculated in spore suspensions prior to treatment with 20 and 40 ppm of ClO2 for 0–60 min, fungal populations significantly decreased at the tested concentrations for 30–60 min. Taken together, these results showed that ClO2 gas can effectively inhibit fungal growth and disease development caused by F. oxysporum f. sp. batatas on sweetpotato. Therefore, ClO2 gas may be used as a sanitizer to control this fungus during postharvest storage of sweetpotato.

Chlorine dioxide (ClO2) can be used as an alternative disinfectant for controlling fungal contamination during postharvest storage. In this study, we tested the in vitro and in vivo inhibitory effects of gaseous ClO2 against Diaporthe batatas SP-d1, the causal agent of sweetpotato dry rot. In in vitro tests, spore suspensions of SP-d1 spread on acidified potato dextrose agar were treated with various ClO2 concentrations (1-20 ppm) for 0-60 min. Fungal growth was significantly inhibited at 1 ppm of ClO2 treatment for 30 min, and completely inhibited at 20 ppm. In in vivo tests, spore suspensions were drop-inoculated onto sweetpotato slices, followed by ClO2 treatment with different concentrations and durations. Lesion diameters were not significantly different between the tested ClO2 concentrations; however, lesion diameters significantly decreased upon increasing the exposure time. Similarly, fungal populations decreased at the tested ClO2 concentrations over time. However, the sliced tissue itself hardened after 60-min ClO2 treatments, especially at 20 ppm of ClO2. When sweetpotato roots were dip-inoculated in spore suspensions for 10 min prior to treatment with 20 and 40 ppm of ClO2 for 0-60 min, fungal populations decreased with increasing ClO2 concentrations. Taken together, these results showed that gaseous ClO2 could significantly inhibit D. batatas growth and dry rot development in sweetpotato. Overall, gaseous ClO2 could be used to control this fungal disease during the postharvest storage of sweetpotato.

Tomato chlorosis virus (ToCV) is a whitefly-transmitted and phloem-limited crinivirus. In 2013, severe interveinal chlorosis and bronzing on tomato leaves, known symptoms of ToCV infection, were observed in greenhouses in Korea. To identify ToCV infection in symptomatic tomato plants, RT-PCR with ToCV-specific primers was performed on leaf samples collected from 11 tomato cultivating areas where ToCV-like symptoms were observed in 2013 and 2014. About half of samples (45.18%) were confirmed as ToCV-infected, and the complete genome of 10 different isolates were characterized. This is the first report of ToCV occurring in Korea. The phylogenetic relationship and genetic variation among ToCV isolates from Korea and other countries were also analysed. When RNA1 and RNA2 are analysed separately, ToCV isolates were clustered into three groups in phylogenetic trees, and ToCV Korean isolates were confirmed to belong to two groups, which were geographically separated. These results suggested that Korean ToCV isolates originated from two independent origins. However, the RNA1 and RNA2 sequences of the Yeonggwang isolate were confirmed to belong to different groups, which indicated that ToCV RNA1 and RNA2 originated from two different origins and were reassorted in Yeonggwang, which is the intermediate point of two geographically separated groups.

The full-genome sequences of fourteen isolates of Broad bean wilt virus 2 (BBWV2), collected from broad bean, pea, spinach, bell pepper and paprika plants in Korea during the years 2006–2012, were determined and analyzed comparatively along with fifteen previously reported BBWV2 genome sequences. Sequence analyses showed that RNA-1 and RNA-2 sequences of BBWV2 Korean isolates consisted of 5950–5956 and 3568–3604 nucleotides, respectively. Full-length genome sequence-based phylogenetic analyses revealed that the BBWV2 Korean isolates could be divided into three major groups comprising GS-I (isolates BB2 and RP7) along with isolate IP, GS-II (isolates BB5, P2, P3 and RP3) along with isolate B935, and GS-III including 16 BBWV2 Korean isolates. Interestingly, GS-III appears to be newly emerged and predominant in Korea. Recombination analyses identified two recombination events in the analyzed BBWV2 population: one in the RNA-1 of isolate K and another one in the RNA-2 of isolate XJ14-3. However, no recombination events were detected in the other 21 Korean isolates. On the other hand, out of 29 BBWV2 isolates, 16 isolates were found to be reassortants, of which each RNA segment (i.e. RNA1 and RNA2) was originated from different parental isolates. Our findings suggested that reassortment rather than recombination is a major evolutionary force in the genetic diversification of BBWV population in Korea.