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Garlic (Allium sativum L.) is one of the oldest horticultural crops and an important element for cuisines worldwide, especially in Korea. After isolating several black aspergilli from brownish lesions with black spores on garlic bulbs, we identified a representative isolate GL-125 through molecular analysis of its internal transcribed spacer (ITS)1-5.8S rRNA-ITS2 region, β-tubulin gene, and calmodulin gene. Morphological features of GL-125 were also compared with those of the Aspergillus awamori type strain NRRL 4948T. As a result, GL-125 was identified as A. awamori by neighbor-joining and maximum-likelihood methods with the examined gene sequences. The macro-morphological (colony growth and color) and micro-morphological (stripes, vesicles, metulae, phialides, and conidia) features of GL-125 were also similar, compared with those of NRRL 4849T. Furthermore, we conducted pathogenicity tests for GL-125 and NRRL 4948T against garlic cloves, using pin-prick inoculation with spore suspensions. Both GL-125 and NRRL 4948T were pathogenic on garlic cloves producing brown to pinkish sunken, water-soaking lesions with white mycelia and black spores in the center. These isolates were successfully re-isolated from the lesions, thereby fulfilling Koch's postulates, whereas no fungal mycelia were isolated from water-inoculated cloves (control). The identities of the re-isolated mycelia were re-confirmed by sequence analyses of the previously examined genes. To the best of our knowledge, this is the first report of A. awamori as a fungal pathogen of garlic.

In 2009 and 2010, the effect of delayed planting on bacterial pustule (Xanthomonas axonopodis pv. glycines) and wildfire (Pseudomonas syringae pv. tabaci) in four soybean cultivars was evaluated in fields in Suwon and Naju, Korea. Soybean was planted on 15 May as the first (traditional) planting date; then, planting was delayed at approximately 15-day intervals (three times) after the first planting. In plots planted approximately 15 or 30 days after the traditional planting date, the disease incidence in highly (Saeolkong and Taegwangkong) and moderately (Pungsannamulkong) susceptible cultivars was significantly reduced under moderate disease pressure, but disease reduction in highly susceptible cultivars was sometimes diminished especially against bacterial pustule under high disease pressure. Altered planting date had no effect on disease incidence in the least susceptible (resistant) cultivar (Cheongja-3-ho), regardless of disease pressure. Consistent differences in disease occurrence were not observed between planting locations. The results from this study indicate that delayed soybean planting reduced the bacterial disease incidence and differentially affected resistant and susceptible cultivars. Thus, planting resistant cultivars at the optimal planting date is desirable, but in the case of susceptible cultivars, delayed planting could be considered along with application of other control measures such as agrochemicals.

The efficacy of resistance in tomato plants, induced by rhizobacteria isolated from Jeju Island in Korea, against late blight disease caused by Phytophthora infestans was tested. Among the bacterial isolates tested, pre-inoculation with four isolates induced an effective defense against late blight. The four isolates, TRH423-3, TRH427-2, KRJ502-1 and KRY505-3, were identified as Burkholderia gladioli, Miamiensis avidus, Acinetobacter quenomosp and Bacillus cereus, respectively, by sequencing the ribosomal intergenic spacer region. They also promoted the growth of tomato seedlings. To illustrate resistance mechanisms, the infection process by P. infestans was examined using a fluorescence microscope. There were no noticeable differences in the rate of germination and appressorium formation between the untreated and pre-inoculated plants. However, callose was more frequently formed at the penetration sites on the leaves of pre-inoculated plants than the untreated plants, suggesting that these rhizobacterial isolates induce defense responses against P. infestans.

In this study, we evaluated and compared the virulence of Magnaporthe oryzae isolates sensitive and resistant to the phosphorothiolate fungicides, edifenphos and iprobenfos on rice plants treated with or without fungicides. Monoconidial isolates of M. oryzae sensitive and resistant to the fungicides were selected from our previous relative mycelial growth assay of 1080 isolates on fungicide-amended media. When six-leaf stage rice plants treated with different concentrations of the fungicides were inoculated with four resistant and four sensitive isolates of M. oryzae , the lowest concentrations showing virulence differences were twice the minimum inhibitory concentrations (MICs) of edifenphos (40 μg a.i. ml −1 ) and iprobenfos (110 μg a.i. ml −1 ). Therefore, two MICs were used as discriminatory concentrations for further virulence tests of 20 sensitive and 20 resistant isolates of M. oryzae . Isolates resistant to edifenphos produced greater disease severity and susceptible lesion number per leaf area (SLNLA) than sensitive isolates on rice plants regardless of treatments. Reduction of disease severity and SLNLA was greater for sensitive than resistant isolates on edifenphos-treated plants compared to untreated controls. Similar results were obtained with iprobenfos, but disease severity or SLNLA of resistant isolates were not affected by iprobenfos compared to untreated controls. In this study, it was evident that resistant isolates of M. oryzae were more virulent than sensitive isolates on rice plants and were less affected by the phosphorothiolate fungicides. Therefore, rice blast management programs should consider a potential adaptation in M. oryzae populations for increased phosphorothiolate-fungicide resistance.

In this study, the sensitivity of Magnaporthe oryzae isolates from different geographic areas in Korea to two phosphorothiolate (PTL) fungicides, edifenphos and iprobenfos, was determined. A total of 1080 M. oryzae isolates were collected from rice-cultivating fields in 11 locations throughout Korea in 1997 and 1998. The minimum inhibitory concentrations (MICs) of edifenphos (20 μg a.i. ml −1 ) and iprobenfos (55 μg a.i. ml −1 ) against seven representative sensitive isolates of M. oryzae were determined from the dose-response curves, and the MICs were then used as single discriminatory concentrations for the detection of fungicide resistance. Of the 1080 tested isolates, the isolates less sensitive to edifenphos and iprobenfos were 57 and 84%, respectively, and 53% of the isolates were less sensitive to both fungicides. Approximately 11% of all tested isolates showed no growth at the MICs of the tested fungicides. Isolates with a relative mycelial growth of 0.05 to edifenphos occurred at the greatest frequency (33%); isolates with a relative growth of 0.3 to iprobenfos occurred at the greatest frequency (23%). The frequency distribution of isolates sensitive to either edifenphos or iprobenfos varied with geographic location. The two-sample median test yielded high medians in the Kwangju and Chonju isolates for edifenphos, and in the Kwangju, Donghae, and Yangyang isolates for iprobenfos, but low medians in the Kangnung isolates for edifenphos and in the Kangnung, Gwangju, and Chunchon isolates for iprobenfos, respectively, as compared to the isolates from the other locations. Analysis of Spearman's rank correlation test showed a significantly positive relationship ( r = 0.490, P M. oryzae populations collected from different geographic areas in Korea, and isolates less sensitive to these fungicides exhibit cross-resistance with each other.

This research was conducted to develop a sequential screening procedure for bacteria antagonistic against Phytophthora capsici, and to evaluate control efficacy by candidate antagonistic bacteria selected by this procedure against Phytophthora blight of pepper in the field. A total of 231 bacterial strains were isolated from soils and roots of cucumber, pepper, and tomato plants grown in fields at 12 locations in Korea in 2000 and 2001. From these, 88 strains were pre-selected using a radicle assay. These strains were then screened in a seedling assay with 2-week-old pepper seedlings inoculated with 1000 zoospores of P. capsici g−1 potting mixture, a concentration which caused complete death of the seedlings. Based on the results of this screen, 15 potentially antagonistic strains with at least 50% control efficacy of seedling infection by P. capsici were selected and further tested in 5-week-old pepper plants. In the in planta trials, four bacterial strains, KJ1R5, KJ2C12, KJ9C8, and 11S16, consistently showed significant (P=0.05) disease suppression against P. capsici infection and were examined as candidate biocontrol agents for their antagonistic effects in the field by artificial inoculation in 2001 and 2002. Plants treated with the bacterial strains KJ1R5, KJ2C12, and KJ9C8 had significantly (P=0.05) lower disease severity and incidence than untreated controls in at least one test. These field test results have demonstrated that the radicle and seedling assays are very effective as part of the screening procedure to select candidate antagonistic bacteria against P. capsici on pepper. Therefore, effective biocontrol agents for Phytophthora blight of pepper could be selected through the sequential screening procedure developed in this study.

A severe epidemic of basal stem rot of the cactus Hylocereus trigonus occurred in 2001, in greenhouses of Goyang City, South Korea, possibly due to continuous cultivation in soil beds. Fusarium oxysporum was isolated and its pathogenicity was demonstrated. Inoculation of mycelial plugs on stem disks of cactus showed brown discoloration. Inoculation of a spore suspension of F. oxysporum (1.40×104 or 1.24×108 spores ml−1) on the underground basal stems of cactus plants, followed by incubation at 28 °C in a growth chamber, led to the development of brown spots identical to the original symptoms after 3 months. The effect of amendment with spent mushroom sawdust, calcium cyanamide, straw and solarization on the development of the disease was studied. In a greenhouse study, amendment with spent mushroom sawdust compost to the disease-conducive soil reduced the disease incidence to 3–12%, as compared to 44–59% with the unamended disease-conducive soil. Autoclaved spent mushroom sawdust compost did not reduce the disease incidence. The bacterial (1.95×1011 cfu g−1) and fungal population (9.50×107 cfu g−1) of spent mushroom sawdust was significantly higher than those (2.0×109 cfu g−1 and 0.13×105 g−1 for bacteria and fungi, respectively) of disease-conducive soil. Also, disease-suppressive soil had a higher fungal population (1.25×105 cfu g−1) compared to disease-conducive soil (0.13×105 cfu g−1). This trend was repeated in the second experiment. Solarization with and without calcium cyanamide of disease-conducive soil reduced effectively pathogen population and disease development, resulting in 16–53% disease incidence, as compared to 81% in the untreated control. Rice straw as an organic amendment did not have synergistic effect on disease control when it was used along with calcium cyanamide for solarization. The results indicate that the control of basal stem rot with spent mushroom sawdust compost may be due to biological activity, and that solarization with calcium cyanamide is a highly effective tool for controlling basal stem rot.