Molecular characterization of Acidovorax citrulli strain NIHHS15-280 causing bacterial fruit blotch disease in Korea and screening of resistance sources in melon (original) (raw)
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Tropical Plant Pathology, 2014
Melon and watermelon bacterial fruit blotch, incited by Acidovorax citrulli, is limited to some areas in Brazil but causes important losses, mainly in melon-producing regions. Although genetic diversity has been observed among strains belonging to the species, they are considered a homogeneous group based on the fact that they show only slight physiological or nutritional differences. The objective of this study was to compare Brazilian strains from melon and watermelon by means of biochemical, pathogenicity, serological and molecular assays. Fifteen biochemical tests, cross inoculation between strains and hosts, ELISA and repetitive sequence analysis (rep-PCR) with the primers REP, ERIC and BOX were conducted. No differences were revealed by nutritional characterization or serology, but cross inoculation showed different pathogenicity groups, which could explain high aggressiveness of the bacteria to melon crops in some regions. Molecular analysis by BOX-PCR clustered strains according to their geographical origin, while ERIC-and REP-PCR, analyzed together, indicated genetic diversity, but without geographical or host origin relationships. One test that could be used to verify the pathogenicity of strains by inoculating detached leaf petioles, showing results in 36 h, is proposed here.
European Journal of Plant Pathology, 2009
Bacterial fruit blotch (BFB) of cucurbits, caused by Acidovorax avenae subsp. citrulli, is a serious threat to the watermelon and melon industries. To date, there are no commercial cultivars of cucurbit crops resistant to the disease. Here we assessed the level of tolerance to bacterial fruit blotch of various commercial cultivars as well as breeding and wild lines of melon, using seed-transmission assays and seedling-inoculation experiments. Selected cultivars were also tested in a greenhouse experiment with mature plants. All tested cultivars/lines were found to be susceptible to the pathogen, and most of them showed different responses (relative tolerance vs. susceptibility) in the different assays; however, some consistent trends were found: cv. ADIR339 was relatively tolerant in all tested assays, and cv. 6407 and wild lines BLB-B and EAD-B were relatively tolerant in seed-transmission assays. We also provide evidence supporting a strong correlation between the level of susceptibility of a cultivar/line and the ability of the pathogen to adhere to or penetrate the seed. To the best of our knowledge, this is the first attempt to assess melon cultivars/lines for bacterial fruit blotch response.
Plant disease, 2005
The gram-negative bacterium Acidovorax avenae subsp. citrulli, formerly Pseudomonas pseudoalcaligenes subsp. citrulli, is the causal agent of bacterial fruit blotch (BFB) of cucurbits (22,30). Although the disease was first reported in 1965 in watermelon seedlings of several plant introduction lines in Georgia, in the United States (24), BFB gained importance after devastating outbreaks in watermelon fields in the Mariana Islands (28), Indiana (13), and Florida (23) in the late 1980s. Since then, BFB has emerged as a major threat to watermelon in the southeastern and midwestern United States. In recent years, significant economic losses caused by A. avenae subsp. citrulli on other cultivated cucurbits, including melon, cucumber, squash, and pumpkin, have been reported in many parts of the world, including the United States,
Colonization dynamics of Acidovorax citrulli in melon
Tropical Plant Pathology, 2010
The aim of this work was to investigate the ability of Acidovorax citrulli, the causal agent of bacterial fruit blotch (BFB) of cucurbits, to colonize melon tissues. Under greenhouse conditions leaves and seeds were inoculated with a spontaneous mutant of A. citrulli (group I) resistant to rifampicin (Ac1 Rif), and samples of hypocotyls, cotyledonary leaves, roots, leaves and stems were processed at three-day intervals. When the 1 st pair of melon leaves had been inoculated, A. citrulli was only detected until the 10 th pair of leaves (1.3 x 10 3 CFU g-1 of leaf) and the consecutive stem (3.3 x 10 3 CFU g-1 of stem) on the 30 th day. However, after seed inoculation A. citrulli colonized the hypocotyl, roots, cotyledonary leaves, leaves and stems and was only detected until the 4 th pair of leaves (1.62 x 10 2 CFU g-1 of leaf) and the consecutive stem (9.1 x 10 1 CFU g-1 of stem) on the 24 th day post-inoculation. In conclusion, A. citrulli colonized different parts of the melon plant over time, depending on its initial location, leaves or seed. This confirms what has been observed in the field, that expanded leaves and stems are the main inoculum sources for melon blossoms and fruit, therefore providing scientific bases for developing more effective strategies for BFB management.
Hortscience, 2011
Bacterial fruit blotch (BFB) caused by the bacterium Acidovorax avenae subsp. citrulli (Aac) is a seed-borne disease that threatens most cucurbit crops. Although limited resistance has been found in a small number of Plant introductions (PIs) in watermelon (Citrullus spp.), there are no reports of high levels of resistance in germplasm lines of Cucumis spp. In this study, 332 Cucumis spp. PIs were screened for resistance to Aac using a newly developed seed vacuum-infusion assay. Significant differences in the reaction of the PI to BFB were observed. The majority of lines were found to be extremely susceptible to the disease. However, several PIs with lower levels of resistance were also identified. Variability in the reaction of plants within each PI was also observed. Of the 332 PI tested, 16 were selected for additional evaluation using a standard spray inoculation tests. PI 353814, PI 381171, PI 536573, and PI 614401, all belonging to C. melo, and PI 504558 (C. ficifolius) were found to have significantly greater levels of resistance than susceptible control cultivars or other PIs in two independent spray inoculation tests. Germplasm lines developed from these PIs may be useful as sources of resistance to BFB in Cucumis breeding programs.
Selection of watermelon genotypes for resistance to bacterial fruit blotch
Euphytica, 2013
Bacterial fruit blotch, caused by Acidovorax citrulli, is a serious threat to the watermelon crop in Brazil. To date, there are no disease-resistant varieties, thus requiring research seeking sources of resistance. To select genotypes with potential use in the management of fruit blotch, the resistance level of watermelon genotypes belonging to the Cucurbits Germplasm Active Bank for the Brazilian Northeast (Banco Ativo de Germoplasma de Cucurbitáceas para o Nordeste Brasileiro-BAG) of Embrapa Semiárido was evaluated at different plant developmental stages: seeds (74 genotypes), seedlings and plants before flowering (29 genotypes) as well as plants during flowering and fruiting (seven genotypes). The genotypes were evaluated for the incidence or severity of the disease, which was estimated with the aid of descriptive scales. Additionally, A. citrulli transmission was determined in seeds derived from symptomatic and asymptomatic fruits. No watermelon genotype was immune to fruit blotch, and the majority showed variations in resistance responses. However, the genotypes BGCIA 979, BGCIA 34 and Sugar Baby showed high levels of resistance at most stages of plant development, thereby suggesting that these genotypes possess fruit blotch resistance genes that could be used in breeding programs. Seeds from symptomatic and asymptomatic fruits of the seven tested genotypes showed transmission rates of A. citrulli up to 35.3 % and 8.7 %, respectively. These results confirm that asymptomatic fruits can harbor contaminated seeds that are responsible for the transmission of the bacteria.
Occurrence, isolation, and identification of Acidovorax citrulli from Melon in Turkey
Plant Protection Science, 2014
During February and August of 2010 and 2011, disease symptoms were detected in melon (Cucumis melo cv. Surmeli) fields and commercial nurseries in Adana and Mersin provinces (Eastern Mediterranean Region, Turkey). Lesions on leaves and fruits were observed in nearly 75 and 85 acres production areas of melon in 2010 and 2011, respectively. Initial symptoms were water-soaked irregular spots, light brown to reddish spots advancing through veins on leaves, small water-soaked lesions, greasy, dark olive green colour areas on the surfaces of melon fruit followed by brown lesions, softening, and cracks. Thirty-five non-fluorescent, slow-growing, round, cream and Gram-negative bacterial isolates were isolated from symptomatic plant materials. The pathogenicity of the isolates was proved using melon seedlings and fruits. According to classical, serological, and molecular assays, the causal organism was identified as Acidovorax citrulli. To the best of our knowledge, this is the first report ...
A study was carried out on the fruit rot of watermelon (Citrullus lanatus (Thunb.) Matsum. Nakai) in Ilorin, Nigeria between February and May, 2008. A large area planted to watermelon in Obbo-ille, a town near Ilorin, Kwara State was severely infected with both leaf and fruit blotches. Both diseases occurred together in all infected watermelon stands. Leaf and fruit samples were taken to the laboratory at the University of Ilorin, for investigation. A bacterial isolate identified as Pseudomonas pseudoalcaligenes Stanier (= Acidovorax avenae) was recovered from both infected leaf and fruit samples. Koch's postulates were performed on both samples using a suspension of the culture isolate. Symptoms were produced on artificially inoculated leaves and fruits and P. pseudoalcaligenes was also re-isolated. This organism was, therefore, identified as the causal organism of bacterial fruit and leaf blotch in watermelon in Ilorin, Kwara State of Nigeria.
An improved assay for detection of Acidovorax citrulli in watermelon and melon seed
Seed Science and Technology, 2009
Acidovorax citrulli (Ac), the causal agent of a bacterial seedling blight and fruit blotch, has emerged as a serious seedborne pathogen of watermelon and melons worldwide. Although attempts have been made to develop a simple routine laboratory seed assay to detect the organism in seeds, none is routinely used. Seeds contaminated with Ac remain a problem for the seed industry. We describe a combined agar plating, real-time PCR assay for detection of Ac in watermelon and melon seeds. The bacteria were extracted by soaking seeds in buffer containing vancomycin and assayed by dilution plating onto semiselective ethanol bromcresol purple /brilliant blue R (EBB) agar and onto EBB agar containing ampicillin (EBBA), by direct real-time PCR, and by realtime BIO-PCR (enrichment PCR). Using extracts of 1,000 healthy seeds spiked with a pure culture suspension of cells of Ac, the BIO-PCR assay using EBBA agar detected Ac in extracts containing as few as one cell per ml. When replicates of 1,000 healthy seeds were spiked with a single naturally infected seed, all the laboratory assays, including plating onto EBB and EBBA agar, direct PCR, and BIO-PCR were positive. This combined agar plating, real-time PCR protocol should prove useful as a routine assay for detection of Ac in watermelon and melon seeds, even in those samples containing relatively high levels of saprophytic bacteria.