Ji Hee Han

Virulence of Entomopathogenic Fungi Metarhizium anisopliae and Paecilomyces fumosoroseus for the Microbial Control of Spodoptera exigua

Abstract The beet armyworm Spodoptera exigua (Lepidoptera: Noctuidae) is difficult to control using chemical insecticides because of the development of insecticide resistance. Several pest control agents are used to control the beet armyworm. Entomopathogenic fungi are one of the candidates for eco-friendly pest control instead of chemical control agents. In this study, among various entomopathogenic fungal strains isolated from soil two isolates were selected as high virulence pathogens against larva of beet armyworm. Control efficacy of fungal conidia was influenced by conidia concentration, temperature, and relative humidity (RH). The isolates Metarhizium anisopliae FT83 showed 100% cumulative mortality against second instar larvae of S. exigua 3 days after treatment at 1 × 107 conidia/mL and Paecilomyces fumosoroseus FG340 caused 100% mortality 6 days after treatment at 1 × 104 conidia/mL. Both M. anisopliae FT83 and P. fumosoroseus FG340 effectively controlled the moth at 20~30°C. M. anisopliae FT83 was significantly affected mortality by RH: mortality was 86.7% at 85% RH and 13.4% at 45% RH. P. fumosoroseus FG340 showed high mortality as 90% at 45% RH and 100% at 75% RH 6 days after conidia treatments. These results suggest that P. fumosoroseus FG340 and M. anisopliae FT83 have high potential to develop as a biocontrol agent against the beet armyworm.

Influence of Additives on the Yield and Pathogenicity of Conidia Produced by Solid State Cultivation of an Isaria javanica Isolate

Abstract Recently, the Q biotype of tobacco whitefly has been recognized as the most hazardous strain of Bemisia tabaci worldwide, because of its increased resistance to some insecticide groups. As an alternative control agent, we selected an Isaria javanica isolate as a candidate for the development of a mycopesticide against the Q biotype of sweet potato whitefly. To select optimal mass production media for solid-state fermentation, we compared the production yield and virulence of conidia between 2 substrates (barley and brown rice), and we also compared the effects of various additives on conidia production and virulence. Barley was a better substrate for conidia production, producing 3.43 × 1010 conidia/g, compared with 3.05 × 1010 conidia/g for brown rice. The addition of 2% CaCO3 + 2% CaSO4 to barley significantly increased conidia production. Addition of yeast extract, casein, or gluten also improved conidia production on barley. Gluten addition (3% and 1.32%) to brown rice improved conidia production by 14 and 6 times, respectively, relative to brown rice without additives. Conidia cultivated on barley produced a mortality rate of 62% in the sweet potato whitefly after 4-day treatment, compared with 53% for conidia cultivated on brown rice. The amendment of solid substrate cultivation with additives changed the virulence of the conidia produced; the median lethal time (LT50) was shorter for conidia produced on barley and brown rice with added yeast extract (1.32% and 3%, respectively), KNO3 (0.6% and 1%), or gluten (1.32% and 3%) compared with conidia produced on substrates without additives.

Biological Control of Aphid Using Fungal Culture and Culture Filtrates of Beauveria bassiana

Abstract Aphids are one of the most destructive pests in crop production such as pepper, cucumber, and eggplants. The importance of entomopathogenic fungi as alternative pest control agents is increasing. Conidia of entomopathogenic fungi are influenced by environmental conditions, such as temperature and relative humidity, and cause slow and fluctuating mortality. These factors have prevented wider application and use of biocontrol agents. For investigation of means of mitigation of such problems, we conducted bioassays with 47 fungal culture filtrates in order to evaluate the potential of secondary metabolites produced by entomopathogenic fungi for use in aphid control. Among 47 culture filtrates cultured potato dextrose broth, filtrate of Beauveria bassiana Bb08 showed the highest mortality (78%) against green peach aphid three days after treatments. Filtrate of Bb08 cultured in Adamek’s medium showed higher toxicity as 100% to third instar nymphs of the aphid compared with seven other filtrates cultured in different broths amended with colloidal chitin or oil. The culture filtrates and fungal cultures from media amended with colloidal chitin or oil had lower control efficacies than filtrates without these additives in three different media. These results indicate that the fungal culture fluid or culture filtrate of B. bassiana Bb08 cultured in Adamek’s medium has potential for development as a mycopesticide for aphid control.

Selection of Carbon, Nitrogen Source and Carrier for Mass Production of Beauveria bassiana

For mass production of entomopathogenic fungus Beauveria bassiana 149, isolated from moth larva, by two-phase fermentation, we performed selection of carbon and nitrogen sources for liquid culture and examined solid fermentation on carrier, ingredient, temperature, and water content. Spore production with rice powder, corn powder, and starch from sweet potato was higher than that of sucrose and dissolvable starch for liquid fermentation as first-phase fermentation. As a nitrogen source, addition of peptone and yeast powder showed higher spore production than , fish powder, and soybean powder. The isolate produced more conidia in sawdust + wheat bran + corn powder, sawdust + wheat bran and rice shell + wheat bran as carrier and ingredient than vermiculite as carrier. Conidia production of B. bassiana 149 in solid-phase fermentation was twice higher at 30 than 20. Conidia yield was higher at 60% and 70% water content ( and ) than 40% and 50% (and ), respectively.

Biological control of Paraconiothyrium minitans CM2 on Lettuce Sclerotinia Rot Caused by Sclerotinia sclerotiorum

A mycoparasite, Paraconiothyrium minitans CM2 was selected for biological control of sclerotinia rot of lettuce caused by Sclerotinia sclerotiorum. The experiment was carried out in a lettuce greenhouse in Yangpyeong from March to April.. When lettuce sclerotinia rot showed in the early stage of occurrence, Conidial suspension of the mycoparasite was weekly treated once to three times onto soil surface around lettuce plants. Incidence of sclerotinia rot in the once-application plot of the mycoparasite (1 × 10 7 spores/ml) and in the benomyl(WP)-treated plot was 11.0% and 2.7%, respectively, whereas that of control was 31.0%. Incidence of twice- and three- appli- cation plots of the isolate was 7.9% and 12.8%, respectively. For increasing the effect of the mycoparasite, the experiment for the timing of application of P. minitans CM2 was carried out in a lettuce greenhouse in Yangpyeong and Suwon. Control efficacy against lettuce sclerotinia rot in the soil-drenching plots of P. minitans CM2 (5 × 10 6 spores/ml) in the planting was 75.3~84.7%, and control effect by treatment of the isolate at the pot drenching+the soil-drenching plots in the early stage of disease occurrence was 63.8~58.0%. As the results, P. minitans CM2 could be a prospective biofungicide for biological control of sclerotinia rot of lettuce.

Effect of Spent Mushroom Substrates of Hericium erinaceum on Plant Pathogens of Tomato

Water extract from spent mushroom substrate of Hericium erinaceus inhibited the mycelial growth of seven strain of tomato pathogenic fungi including Phytophthora capsici and the growth of Ralstonia solanacearum. Control efficacy of tomato bacterial wilt by treatment of 33.3% and 50% water extract from spent mushroom substrate of Hericium erinaceus was showed 58.3%, 83.3%, respectively.

Selection of Bacillus amyloliquefaciens M27 for Biocontrol on Lettuce Sclerotinia Rot

For selection of effective antagonists for control Sclerotinia rot of lettuce, 29 bacteria were isolated from soil in Korea. The bacterial isolates M27 and RM43 identified as Bacillus sp, were selected as prospective agents for inhibiting mycelial growth of Sclerotinia sclerotiorum and Sclerotinia minor. Among the selected isolates, Bacillus amyloliquefaciens M27 effectively suppressed incidence of Sclerotinia rot by Sclerotinia sclerotiorum and Sclerotinia minor in the lettuce nursery.

Influence of Fungicide on the Spore Germination and Mycelial Growth of Beauveria bassiana GHA

This study was conducted to test effect of fungicides on the spore germination and mycelial growth of BotaniGard(Beauveria bassiana GHA). Eight fungicides, which are using for plant disease control in cucumber cultivation, with different concentration were mixed with conidia of GHA isolate for 0.5, 2, and 4 hours. The fungicides trifluminazol, fenarimol, ethaboxam, copper hydroxide and tetraconazol did significantly not inhibit on spore germination and mycelial growth. The trifluminazol, propineb and tetraconazol on high concentrations inhibited the mycelial growth of GHA. However, mixing time of fungicide with conidia of GHA did not affect in spore germination and mycelial growth. These results suggest that fungicide effect needed be checked before mycopesticide is applied in the field.

Selection of Bacillus amyloliquefaciens CC110 for Biological Control of Cucumber Downy Mildew Caused by Pseudoperonospora cubensis

In order to select antagonists for biological control of downy mildew of cucumber, 126 bacteria were isolated from cucumber plants collected from several locations in Korea. Among them, Five isolates were selected as potential biocontrol agents of cucumber downy mildew using a leaf disc bioassay method. In preventive and curative effect tests, the isolate CC110 was found to be effective to control downy mildew on cucumber showing diseased area by 0% whereas that of control was 15.0~18.0%. A bacterium isolate CC110 was identified as Bacillus amyloliquefaciens subsp. plantarum based on phylogenetic analysis using gyrB gene sequence. The culture liquid of isolate CC110 in TSB media were more effective for the control of the disease than those cultured in LB, NB, and KB media in leaf disk bioassay. when undiluted liquid, two-fold, five-fold diluted culture broth, and undiluted liquid, two-fold, five-fold diluted filtrate of isolate CC110 in TSB media were treated, diseased area of cucumber powdery mildew were 0%, 3.0%, 8.0%, 0%, 4.0% and 7.0%, respectively, whereas diseased area in the control was 21.0%. In the cucumber seedling tests, when the culture broth of isolate CC110 in TSB media was treated, diseased area were 35.0%, whereas that of control was 82.0%. When B. amyloliquefaciens CC110 was treated four times at five-day interval in the vinylhouse test, the control effect of cucumber downy mildew was higher than that treated three at seven-day interval.

Biological Control of Paraconiothyrium minitans S134 on Garlic White Rot Caused by Sclerotium cepivorum

Sclerotium cepivorum is a causal agent of white rot disease on different plants including Allium species such as garlic. A mycoparasite, Paraconiothyrium minitans S134 was selected for biological control of sclerotinia rot of garlic caused by S. cepivorum. The experiment was carried out in a garlic field in Taean from October in 2011 to June in 2012. Spore suspension of the mycoparasite was treated twice onto soil surface around garlic plants in sowing in 2011 and late Feb. in 2012, and disease rating was made June in 2012. Incidence of white rot in the twice-application plot of the mycoparasite ( spores/mL) and in the fluquinconazole (WP)-treated plot was 6.8% and 0.4%, respectively, whereas that of control was 19.5%. As the results, P. minitans S134 could be a prospective biofungicide for biological control of white rot of garlic.