• Research in Plant Disease
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• v.29 no.4
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• pp.433-439
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• 2023

Bacterial leaf blight in carrot is one of the most important diseases in the worldwide. In the past decade, its introduction into Korea is causing great concern due to the potential damage to carrot crops domestically. This bacterial disease is caused by Xanthomonas hortorum pv. carotae (Xhc). This study aimed to isolate and identify bacterial strains from the soil of carrot farms in Jeju Island. The bacterial isolates showing characteristics similar with those of Xhc were selected when cultured on artificial media. Through DNA sequencing and analysis based on NCBI data, some of the selected bacterial strains were identified as Xhc. Furthermore, the bacterial strains caused the typical symptom of bacterial leaf blight after inoculation on carrot leaves. The results of this study showed the potential establishment of Xhc in the soil of Jeju Island and it may be valuable data for establish a strategy preventing the domestic spread of carrot bacterial leaf blight in the future.

• Research in Plant Disease
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• v.29 no.3
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• pp.251-257
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• 2023

In order to examine the pathogenicity of Alternaria dauci, the causal agent of carrot leaf blight, it is necessary to standardize sporulation conditions to ensure the optimal quantity and quality of spore inoculum. Therefore, in this study, the effects of the growth medium, aeration treatment, and UV treatment with 12-hr photoperiod on the sporulation of A. dauci KACC42997 were investigated. A. dauci KACC42997 was pre-cultured for 7 days in a potato dextrose agar medium at 25℃ in the dark condition. When the pre-culture, after removing aerial mycelia, was re-incubated for 5 days, with simultaneous aeration treatment and 12-hr cycle UV treatment at 20℃, the largest number of spores was produced. One hundred seventy isolates of A. dauci were isolated from major carrot growing regions such as Pyeongchang, Gumi and Jeju and tested for sporulation under the conditions established in this study. Except for 20 strains, all strains produced spores. Statistically significant differences in the extent of sporulation were found among local populations of A. dauci isolates, but no difference was observed in their pathogenicity on carrots.

• The Plant Pathology Journal
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• v.39 no.4
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• pp.409-416
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• 2023

Bacterial leaf blight of carrots caused by Xanthomonas hortorum pv. carotae (Xhc) is an important worldwide seed-borne disease. In 2012 and 2013, symptoms similar to bacterial leaf blight were found in carrot farms in Jeju Island, Korea. The phenotypic characteristics of the Korean isolation strains were similar to the type strain of Xhc. Pathogenicity showed symptoms on the 14th day after inoculation on carrot plants. Identification by genetic method was multi-position sequencing of the isolated strain JJ2001 was performed using four genes (danK, gyrB, fyuA, and rpoD). The isolated strain was confirmed to be most similar to Xhc M081. Furthermore, in order to analyze the genetic characteristics of the isolated strain, whole genome analysis was performed through the next-generation sequencing method. The draft genome size of JJ2001 is 5,443,372 bp, which contains 63.57% of G + C and has 4,547 open reading frames. Specifically, the classification of pathovar can be confirmed to be similar to that of the host lineage. Plant pathogenic factors and determinants of the majority of the secretion system are conserved in strain JJ2001. This genetic information enables detailed comparative analysis in the pathovar stage of pathogenic bacteria. Furthermore, these findings provide basic data for the distribution and diagnosis of Xanthomonas hortorum pv. carotae, a major plant pathogen that infects carrots in Korea.

• Research in Plant Disease
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• v.29 no.4
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• pp.405-413
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• 2023

Bacterial blight of carrot caused by Xanthomonas hortorum pv. carotae (Xhc) is one of the serious diseases of carrot, of which control measures has not been still established in the domestic farm. In this study, in order to select effective sterilizer for bacterial blight of carrots, three antibiotics such as streptomycin, oxolinic acid, kasugamycin, two copper compounds like copper hydroxide and copper sulfate basic and three rhizobacteria Burkholderia gladioli MRL408-3, Pseudomonas fluorescens TRH415-2 and Bacillus cereus KRY505-3 were selected to investigate their direct antibacterial effects using artificial media, aiming to identify effective pesticides against Xhc. Among them, treated medium with antibiotics such as streptomycin, oxolinic acid, and the antagonistic rhizobacteria MRL408-3 were formed inhibition zone. The agrochemicals and the rhizobacteria MRL408-3, which showed antibacterial effects on carrot leaves, pre-treated on the carrot leaves and then inoculated with Xhc. High control effects were shown on the carrot leaves pre-treated with both streptomycin and oxolinic acid. Scanning electron microscopy images of the carrot leaf surfaces showed that the population of bacteria decreased significantly on leaves pre-treated with streptomycin and oxolinic acid. From these results, it can be inferred that antibiotics like streptomycin and oxolinic acid exhibit superior control effects compared to other agents. This study provides valuable insights towards establishing an effective control system for bacterial blight of carrot.

• Research in Plant Disease
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• v.17 no.1
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• pp.95-98
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• 2011

This research was carried out to selection of desirable cultivar for organic cultivation of carrot in Korea. The assay of disease resistance, insect tolerance and rate of bolting were investigated on 32 cultivars of genetic resources of carrot. This experiment was carried out at experimental field and greenhouse of Gangneung-Wonju National University. 'PI 223360' was resistant against powdery mildew. Ten cultivars including 'Oxheart Carrot Heirloom' were moderately resistant, 22 cultivars including 'Long Impeator #58' were susceptible to powdery mildew. Although there was no resistant cultivar against black rot and leaf blight, our results showed that several cultivars have moderate resistance. Thirteen cultivars including 'Oxheart Carrot Heirloom' were having insect (Erythroplusia pyropia) tolerance and 'SA 102' and 'Scarlet Keeper Carrot Rare' were susceptible. According to the investigation of bolting, 6 cultivars including 'Hongsim Ouchon Carrot' were early bolting and 4 cultivars including 'Japanese Imperial Long Carrot' were moderate bolting. Other cultivars were identified as late bolting. From above results, we confirmed that 'Oxheart Carrot Heirloom' was suitable cultivar for organic cultivation among 32 genetic resources of carrot.

• The Plant Pathology Journal
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• v.15 no.2
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• pp.112-118
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• 1999

Eleven species of Pythium were isolated from leaf blight symptoms on creeping bentgrass (Agrostis palustirs Huds.), Kentucky bluegrass (Poa pratenisis L.) and zoysiagrasses (Zoysia japonica Steud., and Z. matrella (L.) Merr.) planted on golf courses in Korea. Mycelial growth on potato carrot agar medium under various temperature conditions indicated that Pythium species obtained in this study could be divided into four groups based on their responses to temperature conditions. P. vanterpoolii was found to favor low temperature conditions with the optimum temperature of $25^{\circ}$, whereas P. aphanidermatum and P. myriotylum favored relatively high temperature conditions with the optimum temperature of $35^{\circ}$. Other species including P. arrhenomanes, P. catenulatum, P. graminicola, P. oligandrum, P. rostratum, P. torulosum, and P. ultimum were the intermediate group with the optimum temperature of 25~$35^{\circ}$. P. periplocum was similar to the intermediate group but the minimum temperature for its mycelial growth was $15^{\circ}$, which was approximately $5^{\circ}$ above that for the intermediate Pythium spp.group. In the pathogenicity tests conducted in the lab using potted plants, P. aphanidermatum, P.a arrhenomanes, P. catenulatum, P. graminicola, P. myriotylum, P. periplocum, P. rostratum, P. torulosum, P. ultimum, and P. vanterpoolii were found to be pathogenic to creeping bentgrass and Kentucky bluegrass. P. aphanidermatum, P. catenulatum, and P. graminicola were frequently isolated from leaf blight symptoms of creeping bentgrass and Kentucky bluegrass in golf courses during the warm and humid periods in July-August. On the other hand, P. vanterpoolii and P. torulosum were frequently isolated during the cool and humid periods in March-May, suggesting both species might be the major causes of leaf blight occurring in the spring time. Zoysiagrass was susceptible to P. arrhenomanes and the heterothallic Pythium sp. (Ht-F), showing stem and crown rot of turf-grasses at poorly drained areas under coool and humid or rainy conditions. P. oligandrum and the heterothallic Pythium sp. (Ht-L) isolated from creeping bentgrass were avirulent to all species of turfgrasses tested in this study.

• Research in Plant Disease
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• v.17 no.3
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• pp.364-368
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• 2011

Gray mold caused by Botrytis cinerea was found on a carrot seedling in a greenhouse and a field at Daegwallryeong, Gangwon Province in 2007-2009. Symptoms included irregular, brown, blight, or chlorotic halo on leaves and petioles of the carrots. Fungal conidia were globose to subglobose or ellipsoid, hyaline or pale brown, nonseptate, one celled, $7.2-18.2{\times}4.5-11\;{\mu}m$ ($12.1{\times}8.3\;{\mu}m$) in size, and were formed on botryose heads. B. cinerea colonies were hyaline on PDA, and then turned gray and later changed dark gray or brown when spores appeared. The fungal growth stopped at $35^{\circ}C$, temperature range for proper growth was $15-25^{\circ}C$ on MEA and PDA. Carrots inoculated with $1{\times}10^5$ ml conidial suspension were incubated in a moist chamber at $25{\pm}1^{\circ}C$ for pathogenicity testing. Symptoms included irregular, brown, water-soaked rot on carrot roots and irregular, pale brown or dark brown, water-soaked rot on leaves. Symptoms were similar to the original symptoms under natural conditions. The pathogen was reisolated from diseased leaves, sliced roots, and whole roots after inoculation. As a result, this is the first report of carrot gray mold caused by B. cinerea in Korea.

• Research in Plant Disease
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• v.26 no.2
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• pp.61-71
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• 2020

With 32 fungicides, it was examined the inhibitory effects on the mycelial growth of Alternaria dauci KACC42997 causing Alternaria leaf blight of carrot. Showing the results of the agar dilution method, the fungicides belonging to C2, C5, G1, E2, and E3 group were excellent in inhibiting mycelial growth. Protective fungicides belonging to M group, except for iminoctadine tris-albesilate, and pyraclostrobin belonging to C3 group were effective in inhibiting spore germination of pathogens. The fungicides included into C2 group inhibiting succinate dehydrogenase activity and the G1 group inhibiting demethylase activity showed the excellent inhibitory effect on mycelial growth but the inhibitory effect of spore germination was very low. However, fluazinam belonging to C5 group was excellent in inhibiting spore germination as well as mycelial growth. Especially, when 100 ㎍/ml of fluxapyroxad belonging to the C2 group was treated, 47.1% of spore formation was inhibited on the medium. In comparison of the resistance factors of 3 fungicide groups, as G, C, and E group, in populations of A. dauci isolates collected from Gumi, Pyeongchang, and Jeju, resistance factor in the population of Jeju was the lowest. However, two isolates resistant to fludioxonil belonging to E2 group were found in the isolate group of Pyeongchang, and both showed cross-resistance to iprodione and procymidone.

• The Korean Journal of Mycology
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• v.25 no.4 s.83
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• pp.276-290
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• 1997

Eleven species of Pythium were identified from 125 isolates collected from leaf blight lesions on creeping bentgrass (Agrostis palustris Huds.), Kentucky bluegrass (Poa pratensis L.), and zoysiagrasses (Zoysia japonica Steud., and Z. matrella (L.) Merr.) at 35 golf courses in Korea in $1990{\sim}1996$. The identified species included P. aphanidermatum, P. arrhenomanes, P. catenulatum, P. graminicola, P. myriotylum, P. oligandrum, P. periplocum, P. rostratum, P. torulosum, P. ultimum var. ultimum, and P. vanterpoolii. Mycological characteristics of sporangia, oogonia, antheridia, and oospores observed on the sucrose-asparagine bentgrass leaf culture medium were described for each species. Of the species, P. arrhenomanes, P. catenulatum, P. gmminicola, P. oligandrum, P. periplocum, P. rostratum, P. torulosum and P. vanterpoolii were reported for the first time in Korea. P. myriotylum, P. rostratum, P. torulosum and P. vanterpoolii showed characteristic colony patterns on the potato-carrot agar medium, which can be used as criteria for species identification of Pythium.

• Research in Plant Disease
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• v.17 no.2
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• pp.148-154
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• 2011

This study was conducted to control the seed borne pathogens (Alternaria spp.) of carrot and to examine the seed germination rate by using 13 environment friendly agricultural materials instead of conventional chemicals for organic cultivation. The growth inhibiting effects on pathogens showed the different responses according to each agricultural material and effective 7 materials against seed borne pathogens were selected. Among 7 materials, the carrot seeds sterilized with plant extracts, Tanger Stop and Land Saver were not germinated at all. The germination rate of seeds sterilized with other materials showed the similar levels with reference chemical (Benlate-T) and non-treated seeds. Infection rates of seeds sterilized with seaweed extract, Bellopper for controlling A. radicina and plant extract, Ssial-100 for A. dauci were similar or low infection rate compared with reference chemical. The germination rate and root length of seeds sterilized with Bellopper and Ssial-100 was similar or superior to those of chemical sterilized seeds. The optimal condition seemed to be a little bit different depending on the concentration of materials. As a result, the sterilization of carrot seeds by using the environment friendly materials could be effectively utilized as a technology to inhibit the infection of seed-borne pathogens.