Young-Nam Yoon

The Effect of Seed-borne Mycoflora from Sorghum and Foxtail Millet Seeds on Germination and Disease Transmission

Abstract The seed-borne mycoflora of sorghum and foxtail millet collected from different growing areas in South Korea were isolated and taxonomically identified using dry inspection, standard blotter and the agar plate method. We investigated the in vitro and in vivo germination rates of disinfected and non-disinfected seeds of sorghum and foxtail millet using sterilized and unsterilized soil. The percent recovery of seed-borne mycoflora from the seed components of sorghum and foxtail millet seeds was determined and an infection experiment using the dominant species was evaluated for seedling emergence and mortality. A higher number of seed-borne fungi was observed in sorghum compared to that of foxtail millet. Eighteen fungal genera with 34 fungal species were identified from the seeds of sorghum and 13 genera with 22 species were identified from the seeds of foxtail millet. Five dominant species such as Alternaria alternata, Aspergillus flavus, Curvularia lunata, Fusarium moniliforme and Phoma sp. were recorded as seed-borne mycoflora in sorghum and 4 dominant species (Alternaria alternata, Aspergillus flavus, Curvularia lunata, Fusarium moniliforme) were observed in foxtail millet. The in vitro and in vivo germination rates were higher using disinfected seeds and sterilized soil. More seed-borne fungi were recovered from the pericarp compared to the endosperm and seed embryo. The percent recovery of seed-borne fungi ranged from 2.22% to 60.0%, and Alternaria alternata, Curvularia lunata and 4 species of Fusarium were isolated from the endosperm and embryo of sorghum and foxtail millet. Inoculation of the dominant seed-borne fungi showed considerable mortality of seedlings. All the transmitted seed-borne fungi might well be a primary source of infection of sorghum and foxtail millet crops.

Large-scale screening of rice accessions to evaluate resistance to bakanae disease

Bakanae disease is an important fungal disease in the world. No rice (Oryza sativa L.) varieties have been found to be completely resistant to this disease. To facilitate accurate, uniform and simultaneous screening of many rice accessions, we developed an inoculation method for microconidia of Fusarium fujikuroi using a tissue embedding cassette and seedling tray. Standards for evaluating the inoculated rice seedlings as healthy or unhealthy were also established. The method was fast and reproducible for accurately evaluating resistance to bakanae disease in rice.

One-step multiplex reverse transcription-polymerase chain reaction for the simultaneous detection of three rice viruses.

Rice stripe virus (RSV), Rice black-streaked dwarf virus (RBSDV), and Rice dwarf virus (RDV) are major rice-infecting viruses in Korea that can cause serious crop losses. A one-step multiplex reverse transcription-polymerase chain reaction (mRT-PCR) was developed for the simultaneous detection of these rice viruses. Three sets of specific primers targeted to the capsid protein coding genes of RSV, RBSDV, and RDV were used to amplify fragments that were 703 bp, 485 bp, and 252 bp, respectively. The one-step mRT-PCR assay proved to be a sensitive and rapid method for detecting the three rice viruses. This method could be used to facilitate better control of rice viruses.

Effects of a Mungbean Cultivar, Jangannogdu on Nymphal Development, Adult Longevity and Oviposition of Soybean Stink Bugs

Nymphal development, adult longevity, and oviposition of six different species of stink bugs were compared on seeds of a soybean cultivar, Taekwangkong, and two mung bean cultivars, Kyungseonnogdu and Jangannogdu in the insect rearing room (, 16L:8D). Nymphs of six species of stink bugs normally developed on Taekwangkong seed. While nymphs of Riptortus clavatus, Halyomorpha halys, and Dolycoris baccarum developed on seeds of Kyungseonnogdu and Jangannogdu normally, all nymphs of Plautia stali, Piezodorus hybneri and Nezara antennata died after 4th instars on Kyungseonnogdu and after 3rd instars on Jangannogdu. Each instar period tended to be increased as nymphal stages were progressed. Nymphal period was shortest on Taekwangkong seed, followed by Kyungseonnogdu and Jangannogdu, irrelevant to stink bugs species. Emergence rate, adult longevity, and preoviposition period of 6 stink bugs were different depending on the reared seeds. Of 6 different species examined, Riptortus clavatus, Halyomorpha halys, and Dolycoris baccarum which fed on Jangannodu did not emerge, Plautia stali, Piezodorus hybneri, and Nezara antennata which fed on Jangannodu did not oviposit.

Complete Genome Sequences of Grapevine Yellow Speckle Viroid 1 and Hop Stunt Viroid Assembled from the Transcriptome of Ixeridium dentatum Plants.

ABSTRACT Here, we report complete genome sequences of grapevine yellow speckle viroid 1 (GYSVd1) and hop stunt viroid (HSVd), members of the family Pospiviroidae, assembled from the transcriptome data generated from Ixeridium dentatum plants. To our knowledge, this is the first report of GYSVd1 and HSVd in I. dentatum.

Attractiveness of stink bugs to color, height and location of aggregation pheromone trap.

Attractiveness of stink bugs to various colors, heights and locations of fish-net traps incorporated with aggregation pheromones was determined. Bean bug, Riptortus pedestris Fabricius, was most attracted to yellow color trap, followed by white, black, green, blue and brown. R. pedestris and one-banded stink bug, Piezodorus hybneri Gmelin, were most attracted to fish-net traps placed 80 cm above the ground regardless of sexes of two species of stink bugs. Between the sexes, however, R. pedestris females were more attracted to 40 and 80 cm above the ground than the males at those heights although the attraction was not significantly different at 120 and 160 cm heights. P. hybneri females tended to be attracted to 40 and 80 cm height traps but the attraction was the opposite at 120 and 160 cm heights. The highest attraction of R. pedestris was observed in a perilla field with no significant difference in the soybean field and border area in which no crop were cultivated between the perilla and soybean fields. R. pedestris was also more attracted to the sweet persimmon orchard than the soybean and medicinal crops fields, which was a significant difference between the two fields.

Change in Occurrence of Rice stripe virus Disease

We surveyed the occurrence of Rice stripe virus (RSV) disease in 672 fields from 29 rice representative area in July 2012 as nationwide survey for RSV occurrence since 2008. We confirmed occurrence of virus disease in 18 areas, in west coast region including Secheon, Taean, Buwan and Cheorwon. RSV incidence rates of plant in Sacheon and Buan were less than 0.01% and 0.15%, respectively, showing similar rate with the nationwide survey carried out in 2008, whereas incidence rate of field declined from 19.9% in 2008 to 4.9% in 2012. Earlier, RSV occurred largely across the southern region of Korea. In 2001, RSV disease was found in Gangwha and Gyeonggi-do, the northern region of Korea. In 2007, RSV appeared in west coast; Buan in Jeollabuk-do and Seocheon in Choongnam-do. After migration of the vector, small brown plant hopper, from China in 2009, RSV is becoming a pandemic.

Selection of Bactericides for Controlling Soybean Bacterial Pustule

Bacterial pustule of soybean (Glycines max) caused by Xanthomonas axonopodis pv. glycines is one of the most prevalent bacterial diseases of soybean. This bacterium shows strong pathogenicity to the plants and distributes throughout Korea. However, no good control measures including bactericides and resistant cultivars are available to control the disease in Korea. Therefore, this study was conducted to develop chemical control method against soybean bacterial pustule. The present study was undertaken to find out the growth inhibitory effect bactericides (8 antibiotics, 2 copper compounds, quinoline, 18 agro-chemicals) on bacterial pustule pathogen. Antibiotics test showed that tetracycline and streptomycin sulfate significantly suppressed the growth of bacterial pustule pathogen. Also, application of oxolinic acid was found to be effective for pathogen inhibition. However, vancomycin, polymyxin B sulfate and copper compounds did not show the positive suppressive effect on growth of the pathogen. Among the eighteen agro-chemicals, streptomycin sulfate + oxytetracyclin (18.8 + 1.5%) WP, oxytetracycline (17%) WP and oxolinic acid (20%) WP were found to be effective for the inhibition of the pathogen in vitro. The selected 5 agro-chemicals were also applied on soybean in field and their control effects against the soybean bacterial pustule were tested. The foliar application of streptomycin sulfate + oytetracyclin WP and oxytetracycline WP on the naturally infected soybean (Taekwangkong) showed high control value (above 70%). Therefore, it is concluded that the bactericides used in this study showed strong inhibitory effect to soybean bacterial pustule and they can be recommend to farmers to control the disease.

New Alternate Host of Rice stripe virus - `Deulmuksae`

Rice stripe virus (RSV) is one of Tenuivirus Group, which is carried by small brown planthopper. There is an outbreak of RSV in South Korea at 20Ot, and 2007. The infection caused by RSV had been investigated on weeds around the rice cultivated areas 13 region and 26 site including Jeonbuk Buan and Chungnam Seocheon. There have a doubt as to alternate host of RSV is total 15 Family and 50 Species including Gramineae 24 species of Duksaepul (Alopecurus aequalis), H. sativum var. vulgare etc.. There is identified the infected RSV in Festuca myuros, Alopecurus aequalis, Hordeum sativum var. vulgare, Trisetum bifidum, Echinochloa crus-galli var. crus-galli, Digitaria ciliaris among this species. Deulmuksae is the overwintering exotic weed which sprout in Autumn and wither in Spring and commonly growed as green manure crop or cover crop. In order to identify the infection rate furthermore, 111 samples which were collected at Buan Gyehwa-myeon region, and 50 samples from Seocheon Maseo-myeon in June, 2008, were ELISA tested. The results are 32 positives from Buan, 28.8% infection rate, 8 positives from Seocheon 16.0% infection rate. RSV infection of Deulmuksae is not reported currently, and follow report first describes the Deulmuksae as an alternate host of RSV.

Viruliferous Rate of the Small Brown Planthopper in the Maize Field Infected with Rice black-streaked dwarf virus

The Rice black-streaked dwarf virus (RBSDV) infected 99-100% of a -maize field in Mungyeong City in 2007. Adjacent to the area is a Persimmon orchard where barley crops were grown under the trees as green manure crops and for soil amendments. The barley acted as winter host to the small brown plant hoppers (SBPH) enabling the insects to survive and pass the winter season. The existence of RBSDV was detected and confirmed by RT-PCR using S9 specific primer. Samples of the insect vector SBPH were collected in the area on May 3, June 7 and, August 4 and the results of the RT-PCR analysis revealed viruliferous insect rates of 2.9, 4.8, and 4.4%, respectively. These observed viruliferous insect rates were similar with those detected in RBSDV infected rice fields.