In Vitro and In Vivo Inhibitory Effects of Gaseous Chlorine Dioxide against Fusarium oxysporum f. sp. batatas Isolated from Stored Sweetpotato: Study II.

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.

In Vitro and In Vivo Inhibitory Effects of Gaseous Chlorine Dioxide Against Diaporthe batatas Isolated from Stored 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.

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

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.

Continuous alkaline pretreatment of Miscanthus sacchariflorus using a bench-scale single screw reactor.

Miscanthus sacchariflorus 'Goedae-Uksae 1' (GU) was developed as an energy crop of high productivity in Korea. For the practical use of GU for bioethanol production, a bench-scale continuous pretreatment system was developed. The reactor performed screw extrusion, soaking and thermochemical pretreatment at the following operating conditions: 3 mm particle size, 22% moisture content, 140 °C reaction temperature, 8 min residence time, 15 g/min biomass feeding and 120 mL/min NaOH input. As a result of minimizing NaOH concentration and enzyme dosage, 90.8±0.49% glucose yield was obtained from 0.5 M NaOH-pretreated GU containing 3% glucan with 10 FPU cellulase/g cellulose at 50 °C for 72 h. The separate hydrolysis and fermentation of 0.5 M NaOH-pretreated GU containing 10% glucan with 10-30 FPU for 102 h produced 43.0-49.6 g/L bioethanol (theoretical yield, 75.8-87.6%). Thus, this study demonstrated that continuous pretreatment using a single screw reactor is effective for bioethanol production from Miscanthus biomass.

The optimized CO2-added ammonia explosion pretreatment for bioethanol production from rice straw.

A CO2-added ammonia explosion pretreatment was performed for bioethanol production from rice straw. The pretreatment conditions, such as ammonia concentration, CO2 loading level, residence time, and temperature were optimized using response surface methodology. The response for optimization was defined as the glucose conversion rate. The optimized pretreatment conditions resulting in maximal glucose yield (93.6 %) were determined as 14.3 % of ammonia concentration, 2.2 MPa of CO2 loading level, 165.1 °C of temperature, and 69.8 min of residence time. Scanning electron microscopy analysis showed that pretreatment of rice straw strongly increased the surface area and pore size, thus increasing enzymatic accessibility for enzymatic saccharification. Finally, an ethanol yield of 97 % was achieved via simultaneous saccharification and fermentation. Thus, the present study suggests that CO2-added ammonia pretreatment is an appropriate process for bioethanol production from rice straw.