On-Sook Hur

Evaluation of Resistance to Ralstonia solanacearum in Tomato Genetic Resources at Seedling Stage

Bacterial wilt of tomatoes caused by Ralstonia solanacearum is a devastating disease that limits the production of tomato in Korea. The best way to control this disease is using genetically resistant tomato plant. The resistance degree to R. solanacearum was evaluated for 285 tomato accessions conserved in the National Agrobiodiversity Center of Rural Development Administration. These accessions of tomato were originated from 23 countries. Disease severity of tomato accessions was investigated from 7 days to 14 days at an interval of 7 days after inoculation of R. solanacearum under greenhouse conditions. A total of 279 accessions of tomato germplasm were susceptible to R. solanacearum, resulting in wilt and death in 70 to 90% of these plants. Two tomato accessions were moderately resistant to R. solanacearum. Only four accessions showed high resistance against R. solanacearum. No distinct symptom of bacterial wilt appeared on the resistant tomato germplasms for up to 14 days after inoculation of R. solanacearum. Microscopy of resistant tomato stems infected with R. solanacearum revealed limited bacterial spread with thickening of pit membrane and gum production. Therefore, these four resistant tomato germplasms could be used in tomato breeding program against bacterial wilt.

Evaluation of Genetic Diversity of Red Pepper Landraces (Capsicum annuum L.) from Bulgaria Using SSR Markers

The amount of genetic variability of a species is essential for its survival and adaptation in different environments, and studies of genetic diversity using molecular markers are necessary to understand the genetic structure of a population and to orientate effective strategies of germplasm conservation. The aim of current study was to determine the SSR markers that can be used rapidly and reliably to evaluated the pepper of Bulgaria landraces, and applied the markers to assessment of introduce genetic diversity of the pepper germplasm. We used 22 polymorphic microsatellite markers to analysis of genetic diversity within 61 pepper collection of Bulgaria landraces germplasm, all SSR primers pairs produced 82 polymorphic and reproducible amplification fragments. Results showed a relatively low level of genetic diversity among pepper accessions from Bulgaria for both molecular and morphological markers. An average value of polymorphic information contents (PIC) were 0.334 with a range of 0.061 to 0.63. The mean values of observed (HO) and gene diversity (GD) were 0.383 and 0.154, respectively, indicating a considerable amount of polymorphism within this collection. A genetic distance-based phylogeny grouped into three distinct groups according to genetic difference among the accessions. An average day of flowering time was 56.9 days with a range of 48 to 65 days. The average of fruit length and width were 6.9cm with a range 2.6 to 13.9cm, and 1.9cm with a range 0.5 to 4.2cm, respectively.

Evaluation of Resistance to Colletotrichum acutatum in Pepper Genetic Resources

Resistance of pepper (Capsicum spp.) to anthracnose (Colletotrichum acutatum) was evaluated during regeneration of Capsicum spp. in National Agrobiodiversity Center. Disease severity of 896 pepper accessions (430 accessions of C. annuum, 219 accessions of C. baccatum, 14 accessions of C. chacoense, 153 accessions of C. chinense, 70 accessions of C. frutescens, 2 accessions of C. pubescens, and unidentified 8 accessions) was investigated at 14 days after inoculation in 28 C humid chamber. Forty nine accessions of pepper germplasm were resistant to C. acutatum. Among them, nine accessions were highly resistant to C. acutatum without wounding spray inoculation. Four accessions belonged to the species C. baccatum, one accession to C. chacoense, and four accessions to C. frutescens. Forty two resistant candidate accessions were inoculated with pin-prick wounding using a syringe needle. Five accessions were resistant as a less than 3% of disease severity to C. acutatum with wounding inoculation 5 days after inoculation. All resistant accessions were C. baccatum. These five pepper germplasm might be used as breeding resources for the anthracnose resistance breeding program.

QTL mapping and GWAS reveal candidate genes controlling capsaicinoid content in Capsicum

Summary Capsaicinoids are unique compounds produced only in peppers (Capsicum spp.). Several studies using classical quantitative trait loci (QTLs) mapping and genomewide association studies (GWAS) have identified QTLs controlling capsaicinoid content in peppers; however, neither the QTLs common to each population nor the candidate genes underlying them have been identified due to the limitations of each approach used. Here, we performed QTL mapping and GWAS for capsaicinoid content in peppers using two recombinant inbred line (RIL) populations and one GWAS population. Whole‐genome resequencing and genotyping by sequencing (GBS) were used to construct high‐density single nucleotide polymorphism (SNP) maps. Five QTL regions on chromosomes 1, 2, 3, 4 and 10 were commonly identified in both RIL populations over multiple locations and years. Furthermore, a total of 109 610 SNPs derived from two GBS libraries were used to analyse the GWAS population consisting of 208 C. annuum‐clade accessions. A total of 69 QTL regions were identified from the GWAS, 10 of which were co‐located with the QTLs identified from the two biparental populations. Within these regions, we were able to identify five candidate genes known to be involved in capsaicinoid biosynthesis. Our results demonstrate that QTL mapping and GBS‐GWAS represent a powerful combined approach for the identification of loci controlling complex traits.

First Report of Fusarium Wilt Caused by Fusarium proliferatum on Safflower

annual plant of the family Asteraceae. Safflower has been widely cultivated in Korea, India, China, Egypt, Southern Europe, North America, and Australia (Lee, 1980). Safflower seeds contain α-linoleic acid, which used as cooking oil and clinically for the treatment of cataclasis, osteoporosis and rheumatoid arthritis in Korea (Kang et al., 1999; Kim, 1992; Lee et al., 2002). In addition, its flower has been utilized for folk medicine as an analgesic, antithrombotic and antihypertensive crude drug, as well as natural dye and food colorants (Han, 1988). It has been reported that main pathogens on safflower are Alternaria alternata (leaf spot), Botrytis cinerea (gray mold), Colletotrichum acutatum (Anthracnose), Fusarium oxysporum (Fusarium wilt), Phytophthora cactorum (Phytophthora root rot), Puccinia carthami (rust), Sclerotium rolfsii (collar rot), and Sphaerotheca fuliginea (powdery mildew) worldwide (Farr and Rossman, 2016). Recently, we observed wilt symptoms on safflower grown in green house in Jeonju, Korea, thus leading to identify the causal agent of the wilt disease in this study.

First Report on Pink Rot of Sunflower (Helianthus annuus) Caused by Trichothecium roseum in Korea

년생 초본식물로 북아메리카 중·서부 지역이 원산지이다 (Heiser, 1951). 땅콩, 콩, 유채 등과 더불어 4대 유지작물 중의 하나로 해바라기씨에는 지방유, 필수아미노산이 풍부하여 혈액순환을 도와주며 비타민 함량이 많아 영양학적으로 우수한 식품으로 권장된다(Baudet과 Mossé, 1977; Škorić 등, 2008; Warner, 2005). 세계적으로 해바라기에서 발병되는 주요 병원으로는 풋 마름병(Ralstonia solanacearum), 검은무늬병(Alternaria spp.), 잿빛곰팡이병(Botrytis cinerea), 노균병(Plasmopara spp.), 녹 병(Puccinia helianthi), 균핵병(Sclerotinia sclerotiorum), 잎마름 병(Septoria helianthi), 흰가루병(Sphaerotheca fusca) 등이 있 다(Farr과 Rossman, 2016). 해바라기 재배포장에서 해바라기 꽃 부분이 감염이 되어 화뢰(head) 부분이 갈변되었으며 줄기까지 퍼져서 검게 변 하였다. 병든 화뢰의 종자로부터 병원균을 순수분리하여 균주를 분리하였으며, 해바라기에 인공접종하여 병원성을 확인하였다. 따라서 본 연구는 해바라기에서 종자의 썩음 병을 일으키는 병의 병징, 균학적 특징, 병원성 검정 및 염기 서열 분석결과를 보고하고자 한다.

Screening of Pumpkin (Cucurbita spp.) Germplasm for Resistance to Powdery Mildew at Various Stages of Seedlings Growth

Powdery mildew is one of the world’s most widespread and damaging diseases of cucurbits (Kousik et al., 2008). It is caused by several species of the Erysiphaceae including Podosphaera xanthii (syn. Sphaerotheca fulginea) (McGrath and Thomas, 1996; Thomas et al., 1984). This disease acts as a sink for plant photosynthates causing reduction in plant growth, premature foliage loss, and consequently a reduction in yield. The yield loss is proportional to the severity of the disease and the length of time that plants have been infected (Mossler and Nesheim, 2005). It also results the reduced vigor of the seedlings and death of the seedlings in some instances (Kousik et al., 2008). In Korea, S. fuliginea is the most prevalent pathogen of powdery mildew in cucurbits (Shin, 2000). To date, seven races of P. xanthii (syn. S. fuliginea) have been identified using melon (Cucumis melo L.) differentials (Cohen et al., 2004; Pitrat et al., 1998; Thomas et al., 1984). Variability within races 1 and 2 in P. xanthii populations was described using 32 melon cultigens with the potential for the existence of 28 races (McCreight, 2006). Physiological races of this pathogen have not been classified for other cucurbits because of the lack of differentials and fully resistant germplasm (Cohen et al., 2004). A powdery mildew isolate from one cucurbit can infect all other tested cucurbit spp. (Hammett, 1977) and Cohen et al. (2004) has provided detail description of the cucurbit powdery mildew pathogen and race classification system. In the past, screening and selection studies against powResearch Article Open Access Res. Plant Dis. 22(3): 133-144 (2016) http://dx.doi.org/10.5423/RPD.2016.22.3.133