scholarly journals First Report of Vine Decline of Mature Watermelon Plants Caused by Olpidium bornovanus

Plant Disease ◽  
2014 ◽  
Vol 98 (6) ◽  
pp. 852-852
Author(s):  
M. E. Stanghellini ◽  
M. Mohammadi ◽  
D. M. Mathews ◽  
S. Adkins
Keyword(s):  
Vascular Tissue ◽  
Citrullus Lanatus ◽  
Morphological Characteristics ◽  
Epidermal Cells ◽  
Soil Conditions ◽  
Root Pathogen ◽  
Olpidium Bornovanus ◽  
Resting Spores ◽  
Vine Decline ◽  
Structural Roots

In late May 2013, collapse of mature watermelon plants (Citrullus lanatus L.) at first harvest occurred in several drip-irrigated commercial fields in the Coachella Valley, California. Above-ground symptoms consisted of chlorosis, wilting, and death of leaves starting at the crown and progressing rapidly towards the tip of vines. Structural roots of collapsed plants appeared healthy but feeder roots exhibited a brownish discoloration. Microscopic examination revealed that almost all epidermal cells of feeder roots contained either sporangia or resting spores of a fungus tentatively identified, based upon morphological characteristics, as Olpidium bornovanus (Sahtiy.) Karling. No other fungi or fungal-like organisms were microscopically observed in or isolated from structural roots, feeder roots, or vascular tissue of collapsed plants. Leaf, root, and peduncle samples from collapsed plants were tested for Melon necrotic spot virus (MNSV), a virus known to be transmitted by O. bornovanus, and Squash vein yellowing virus (SqVYV), a whitefly-transmitted ipomovirus known to cause watermelon vine decline (1). No MNSV was detected using previously described methods (3). No SqVYV was detected by testing total RNA from symptomatic plants (RNeasy Plant Mini Kit, Qiagen, Valencia, CA) with reverse transcription-PCR using previously described primers and methods (1,2). Genomic DNA was extracted from zoospores of the fungus which were obtained from a single-sporangial isolate maintained on watermelon seedlings. Analysis of ITS 1 and 2 gene sequences and a subsequent search in NCBI GenBank revealed a 99% identity to nucleotide sequences for O. bornovanus (Accession Nos. AB205215 and AB665758). To confirm Koch's postulates, roots of three 5-day-old watermelon seedlings were inoculated by exposure to zoospores (~1 × 105) in a beaker for 2 min and then transplanted into pots containing vermiculite. Pots were irrigated daily and incubated in a growth chamber (25°C, 12-h photoperiod). Controls consisted of non-inoculated watermelon seedlings. The experiment was repeated twice. Within 15 days of inoculation, all inoculated plants were stunted, and roots of stunted plants were brown and most root epidermal cells were filled with either sporangia or resting spores of O. bornovanus. Within 30 days of inoculation, 40 to 60% of the inoculated plants died in all three experiments. No other microorganisms were microscopically observed in or isolated from necrotic roots. Control plants remained symptomless over the duration of the study. Although O. bornovanus has been reported as a root pathogen of melons in greenhouse conditions (3), this is the first worldwide report of the fungus as a root pathogen of watermelons and its association with a late season vine decline in the field. Near-saturated soil conditions resulting from a daily irrigation regime during the latter part of the growing season apparently favored extensive root colonization by this indigenous and opportunistic zoosporic fungus, suggesting that growers should exercise care regarding the duration and frequency of irrigation events. References: (1) S. Adkins et al. Phytopathology 97:145, 2007. (2) S. Adkins et al. Plant Dis. 1119, 2008. (3) M. E. Stanghellini et al. Plant Dis. 94:163, 2010.

scholarly journals Adaptability and leaf anatomical features in oil palm seedlings produced by embryo rescue and pre-germinated seeds

2010 ◽  
Vol 22 (3) ◽  
pp. 209-215 ◽  
Author(s):  
Zanderluce G. Luis ◽  
Kadja Milena G. Bezerra ◽  
Jonny Everson Scherwinski-Pereira
Keyword(s):  
Oil Palm ◽  
Embryo Rescue ◽  
Morphological Characteristics ◽  
Growth Conditions ◽  
Epidermal Cells ◽  
In Vitro Cultivation ◽  
Vascular Bundles ◽  
Anatomical Plasticity ◽  
Germinated Seeds

Changes in the leaf structure of plants grown in different conditions have been reported, such as increase in size and density of stomata and reduction in stomatal control, amount of epicuticular wax, and mesophyll thickness, with a high diversity of intercellular spaces. However, these changes are highly variable depending on the physiological and morphological characteristics of each species. The objective of this work was to analyze the adaptability and anatomical plasticity of oil palm seedlings produced after embryo rescue and pre-germinated seeds. Expanded leaves were prepared for evaluation of morphometric data and anatomical structures. It was verified that the environmental conditions in vitro negatively influenced the stomata density, epidermal and hypodermal thickness, and the values for the expansion cells and leaf mesophile. Anatomically, the oil palm leaves present the same tissues composition in both growth conditions, with uniseriate epidermal cells, and tetracitic stomata occurring in both epidermal surfaces. Epidermal cells from in vitro plants are thinner than ones from greenhouse. The midrib of leaves from greenhouse plants are more developed and is composed by only one central vascular bundle, while plants from in vitro cultivation developed three to four collateral vascular bundles.

scholarly journals First Report of Monosporascus cannonballus on Melon in Mexico

Plant Disease ◽  
2012 ◽  
Vol 96 (7) ◽  
pp. 1068-1068 ◽  
Author(s):  
Y. I. Chew-Madinaveitia ◽  
A. Gaytán-Mascorro ◽  
T. Herrera-Pérez
Keyword(s):  
Citrullus Lanatus ◽  
The United States ◽  
Internal Transcribed Spacer Region ◽  
Oat Hulls ◽  
Monosporascus Cannonballus ◽  
First Report ◽  
The North ◽  
Root Necrosis ◽  
Vine Decline ◽  
Melon Seeds

In 2009, 2010, and 2011, melon plants (Cucumis melo L.) exhibited vine decline in commercial fields in the Municipality of Viesca, State of Coahuila, in the north-central region of Mexico known as La Comarca Lagunera. Symptoms included wilting, leaf yellowing, and vine collapse prior to harvest. Diseased plants showed necrotic root lesions and loss of secondary and tertiary roots. Numerous perithecia containing asci and ascospores typical of Monosporascus cannonballus Pollack & Uecker (3) were found in the root system. M. cannonballus is a typical fungus of hot semiarid climates such as La Comarca Lagunera in which daytime temperatures above 40°C are frequent during the melon growing season. Small root pieces were disinfected with 1.5% sodium hypochlorite for 1 min and plated onto potato dextrose agar (PDA) medium with 0.5 g l–1 streptomycin sulfate and incubated for 7 days at 25°C under dark conditions. The mycelium of the fungus colony was initially white, turning gray about 3 weeks later and yielding black perithecia with one ascospore per asci. The internal transcribed spacer region of ribosomal DNA of isolate 4 was sequenced and submitted to GenBank with Accession No. JQ51935. Pathogenicity of this isolate was confirmed on melon plants (cv. Cruiser) in the greenhouse at 25 to 32°C. Fungus inoculum was produced in a sand-oat hull medium (0.5 l of sand, 45 g of oat hulls, and 100 ml of distilled water), and incubated at 25°C for 50 days (1). Melon seeds were sown in sterile sand in 20-cm diameter and 12-cm depth polyurethane containers, and the inoculum was added to produce a concentration of 20 CFU g–1. Sowing was done in five inoculated containers and thinned to two plants per container, each container representing a replication. Plants were also grown in five noninoculated containers that were used as controls. After 50 days under greenhouse conditions, plants were evaluated for disease symptoms. Melon plants inoculated with M. cannonballus exhibited root necrosis as opposed to healthy roots observed in noninoculated plants. M. cannonballus was reisolated from symptomatic plants, confirming Koch's postulates. M. cannonballus causes root rot and vine decline on melon and has been reported in Brazil, Guatemala, Honduras, India, Iran, Israel, Italy, Japan, Libya, the Netherlands (plants from Russia), Pakistan, Saudi Arabia, Spain, Taiwan, Tunisia, and the United States. M. cannonballus was reported in 1996 in southeastern Mexico in the State of Colima, where watermelon (Citrullus lanatus (Thunb.) Matsum.& Nakai) showed wilting and plant collapse prior to harvest (2). However, to our knowledge, this is the first report of M. cannonballus on melon in Mexico. This is relevant because La Comarca Lagunera region is one of the major melon producing areas in Mexico and M. cannonballus is a pathogen that may cause yield losses of up to 100%. References: (1) B. D. Bruton et al. Plant Dis. 84:907, 2000. (2) R. D. Martyn et al. Plant Dis. 80:1430, 1996. (3) F. G. Pollack and F. A. Uecker. Mycologia 66:346, 1974.

scholarly journals First Report of Erysiphe cichoracearum Infecting Hedera canariensis var. azorica in Italy

Plant Disease ◽  
1999 ◽  
Vol 83 (2) ◽  
pp. 198-198
Author(s):  
C. Nali
Keyword(s):  
New York ◽  
Powdery Mildew ◽  
Citrullus Lanatus ◽  
Ornamental Plants ◽  
Morphological Characteristics ◽  
Hedera Helix ◽  
Cucumis Sativus L ◽  
First Report ◽  
Erysiphe Cichoracearum ◽  
English Ivy

A powdery mildew disease of variegated ivy (Hedera canariensis L. var. azorica) was observed on the Tyrrhenian coast in Tuscany (Italy) in spring 1998. Symptoms began as small, nearly circular reddish spots that later enlarged and coalesced. The hyaline mycelium produced abundant, ellipsoid conidia in long chains that ranged from 20 to 40 μm in length and from 12 to 25 μm in width. Cleistothecia were globose (100 to 120 μm diameter), dark brown (when mature) with a basal ring of mycelioid appendages, and contained several (up to 20) ovate asci, each generally containing two ascospores. Ascospores were hyaline, one-celled, ellipsoid (20 to 35 μm in length and 10 to 20 μm in width). The morphological characteristics of this fungus were those given for Erysiphe cichoracearum DC. Infection also was found on English ivy (Hedera helix L.). It is reported that this species is, occasionally, subject to powdery mildew caused by E. cichoracearum (1). Conidia from infected leaves were shaken onto leaves of melon (Cucumis melo L.), cucumber (Cucumis sativus L.), watermelon (Citrullus lanatus [Thunb.] Matsum. & Nakai), lettuce (Lactuca sativa L.), tomato (Lycopersicon esculentum Mill.), tobacco (Nicotiana tabacum L.) and variegated and English ivy. After 7 days, the disease was observed on cucumber, melon, watermelon, tobacco, and variegated ivy. Examination confirmed that test plants were infected with E. cichoracearum. This is the first report of E. cichoracearum on variegated ivy in Italy. Reference: (1) P. P. Pirone. 1970. Diseases and Pests of Ornamental Plants. The Ronald Press, New York.

Melon necrotic spot virus. [Distribution map].

2010 ◽  
Author(s):  
Keyword(s):  
Cucumis Melo ◽  
Citrullus Lanatus ◽  
Necrotic Spot ◽  
Distribution Map ◽  
Spot Virus ◽  
Melon Necrotic Spot Virus ◽  
Olpidium Bornovanus ◽  
Virus Distribution ◽  
New Distribution ◽  
Distribution In Europe

Abstract A new distribution map is given for Melon necrotic spot virus (Tombusviridae: Carmovirus). The hosts include melon (Cucumis melo), cucumber (Cucumis sativus) and watermelon (Citrullus lanatus). Information is given on the geographical distribution in Europe (France, Greece, Crete, Italy, Sardinia, Netherlands, Norway, Spain, Canary islands, mainland Spain, Sweden, UK, England and Wales), Asia (China, Jiangsu, Iran, Israel, Japan, Hokkaido, Honshu, Kyushu, Shikoku, Korea Republic, Syria and Turkey), Africa (Tunisia), North America (Canada, Ontario, Mexico, USA, California) Central America and Caribbean (Guatemala, Honduras and Panama) and South America (Uruguay). The virus is transmitted by the fungal vector Olpidium bornovanus (syn. O. radicale) (Chytridiomycota: Olpidiaceae).

scholarly journals WEEDS AS POTENTIAL HOSTS FOR FUNGAL ROOT PATHOGENS OF WATERMELON

2019 ◽  
Vol 32 (1) ◽  
pp. 1-6 ◽  
Author(s):  
Rui Sales Júnior ◽  
Ana Paula Medeiros dos Santos Rodrigues ◽  
Andreia Mitsa Paiva Negreiros ◽  
Márcia Michelle de Queiroz Ambrósio ◽  
Hailton da Silva Barboza ◽  
...  
Keyword(s):  
Root Rot ◽  
Citrullus Lanatus ◽  
Phytopathogenic Fungi ◽  
Soilborne Pathogens ◽  
Weed Species ◽  
Amaranthus Spinosus ◽  
Trianthema Portulacastrum ◽  
Different Types ◽  
Vine Decline ◽  
Boerhavia Diffusa

ABSTRACT Many watermelon (Citrullus lanatus) diseases are caused by soilborne pathogens in Brazil and worldwide. The goal of this study was to identify and quantify the frequency of phytopathogenic fungi associated with watermelon root rot and vine decline that were also present in the roots of weeds in the major watermelon production regions in the state of Rio Grande do Norte, Brazil. We collected root samples from 10 of the most prevalent weed species in 16 watermelon producing areas. The plants were identified and their frequencies in the fields were calculated. The fungi found in the weed roots were isolated and the main genera associated with watermelon vine decline were identified. We identified 13 weed species belonging to nine botanical families. The weed species with the highest frequencies found in the field were Amaranthus spinosus (25.0%), Trianthema portulacastrum (18.8%), Commelina sp. (18.8%), and Boerhavia diffusa (12.5%). The fungi Macrophomina, Rhizoctonia, and Monosporascus were isolated from the roots of the weed plants. While Macrophomina was isolated from 12 different types of plants, Rhizoctonia and Monosporascus were isolated from four and two different plant species, respectively.

Genetic analysis of partial resistance to vine decline in watermelon [Citrullus lanatus (Thunb.) Matsum&Nakai]

2020 ◽  
Vol 73 (2) ◽  
pp. 361-365
Author(s):  
Siddharood Maragal ◽  
K. Arpitha ◽  
Muttanna Revadi ◽  
Sourav Mahapatra ◽  
K. N. Avinash ◽  
...  
Keyword(s):  
Genetic Analysis ◽  
Partial Resistance ◽  
Citrullus Lanatus ◽  
Vine Decline

scholarly journals First Report of Clubroot on Capsella bursa-pastoris Caused by Plasmodiophora brassicae in Sichuan Province of China

Plant Disease ◽  
2014 ◽  
Vol 98 (5) ◽  
pp. 687-687 ◽  
Author(s):  
L. Ren ◽  
X. P. Fang ◽  
C. C. Sun ◽  
K. R. Chen ◽  
F. Liu ◽  
...  
Keyword(s):  
Plasmodiophora Brassicae ◽  
Tap Water ◽  
Disease Incidence ◽  
Morphological Characteristics ◽  
Pcr Amplification ◽  
Sichuan Province ◽  
Clubroot Disease ◽  
Cruciferous Vegetable ◽  
First Report ◽  
Resting Spores

Shepherd's purse (Capsella bursa-pastoris (L.) Medicus) is an edible and wild medicinal plant widely distributed in China. This plant has been cultivated in Shanghai, China, since the end of the 19th century. Infection of C. bursa-pastoris by Plasmodiophora brassicae, the causal agent of clubroot disease on Brassica spp. has been reported in Korea (2), but is not known to occur in China. In February of 2011, stunted and wilted shepherd's purse (SP) plants were observed in a field planted to oilseed rapes (B. napus) in Sichuan Province of China. Symptomatic SP plants also exhibited root galls. Disease incidence was 6.2% and 100% for SP and B. napus, respectively. Root galls on diseased SP plants were collected for pathogen identification. Many resting spores were observed when the root galls were examined under a light microscope. The resting spores were circular in shape, measuring 2.0 to 3.1 μm in diameter (average 2.6 μm). PCR amplification was conducted to confirm the pathogen. DNA was extracted from root galls and healthy roots (control) of SP. Two primers, TC2F (5′-AAACAACGAGTCAGCTTGAATGCTAGTGTG-3′) and TC2R (5′-CTTTAGTTGTGTTTCGGCTAGGATGGTTCG-3′) were used to detect P. brassicae (1). No PCR amplifications were observed with the control DNA as template. A fragment of the expected size (approximately 520 bp) was obtained when DNA was amplified from diseased roots of SP. These results suggest that the pathogen in the galled roots of SP is P. brassicae. Pathogenicity of P. brassicae in SP was tested on plants of both SP and Chinese cabbage (CC) (B. campestris ssp. pekinensis). A resting spore suspension prepared from naturally infected SP roots was mixed with a sterilized soil in two plastic pots, resulting in a final concentration of 5 × 106 spores/g soil. Soil treated with the same volume of sterile water was used as a control. Seeds of SP and CC were pre-germinated on moist filter paper for 2 days (20°C) and seeded into the infested and control pots, one seed per pot for planted for CC and four seeds per pot for SP. The pots were placed in a chamber at 15 to 25°C under 12 h light and 12 h dark. Plants in each pot were uprooted after 4 weeks and the roots of each plant were washed under tap water and rated for clubroot disease. No disease symptoms were observed in the control treatments of SP or CC. Plants of both species showed symptoms of clubroot, with the disease incidence of 62.5% and 100% on SP and CC, respectively. The pathogen was isolated from diseased roots of each plant and confirmed as P. brassicae based on morphological characteristics and PCR detection. To our knowledge, this is the first report of clubroot disease on C. bursa-pastoris in Sichuan Province of China. This finding suggests that it may be necessary to manage C. bursa-pastoris in cruciferous vegetable (cabbage, turnip) and oilseed rape production fields. References: (1) T. Cao et al. Plant Dis. 91:80, 2007. (2) W. G. Kim et al. Microbiology 39:233, 2011.

Histopathology of infection of bean with Pythium myriotylum compared with infection with other Pythium species

1975 ◽  
Vol 53 (17) ◽  
pp. 1786-1795 ◽  
Author(s):  
Roberta L. Dow ◽  
Robert D. Lumsden
Keyword(s):  
Cell Walls ◽  
Vascular Tissue ◽  
Tap Water ◽  
Pythium Ultimum ◽  
Epidermal Cells ◽  
Pythium Species ◽  
Pythium Myriotylum ◽  
Zoospore Production ◽  
Aerial Hyphae ◽  
Small Clusters

Clusters of abundant appressoria formed from branching hyphae of mycelial inoculum of Pythium myriotylum on the surface of bean hypocotyls and roots. Pythium aphanidermatum usually produced single appressoria, but sometimes small clusters of appressoria. Pythium ultimum produced only single appressoria. Early pathogenesis of all species was characterized by rapid radial growth of hyphae in the epidermal cells, which was more rapid than in the cortex. These hyphae were constricted at the host cell walls. Invaded tissue and adjacent cells stained differently from healthy cells with all isolates. Aerial hyphae were produced from vesicles below the cuticle or within epidermal cells soon after infection was established. Safranin-staining materials were observed in the xylem, phloem, and tannin sacs. Zoospores of P. myriotylum and P. aphanidermatum germinated and produced long prepenetration hyphae, which branched and formed single appressoria. Oospores of P. myriotylum, P. aphanidermatum, and P. ultimum, after germination, produced branched hyphae and single appressoria. Penetration, rapid advance through epidermal cells, and ramification of cortical and vascular tissue were identical with those of mycelial inoculum. Sporangia of all three species formed intercellularly and intracellulary within 48 h and predominantly in the epidermis and upper cortex. Oogonia were produced intercellularly and intracellularly in 4 day s throughout the tissue, but mainly in the inner two thirds of the cortex. Sporangia of P. myriotylum and P. aphanidermatum in infected bean hypocotyls germinated within 3 h when flooded with tap water and produced zoospores within 6 h. When similar tissue was air-dried for 3 days or rapidly dried for 3 h. there was neither germination nor zoospore production.

scholarly journals First Report of Fusarium oxysporum f. sp. lycopersici Race 3 Causing Fusarium Wilt on Tomato in Korea

Plant Disease ◽  
2013 ◽  
Vol 97 (10) ◽  
pp. 1377-1377 ◽  
Author(s):  
H.-W. Choi ◽  
S. K. Hong ◽  
Y. K. Lee ◽  
H. S. Shim
Keyword(s):  
Fusarium Wilt ◽  
Dna Sequences ◽  
Vascular Tissue ◽  
Elongation Factor ◽  
Morphological Characteristics ◽  
Spore Suspension ◽  
Vascular Bundles ◽  
Laboratory Manual ◽  
First Report ◽  
Blastn Analysis

In July 2010, fusarium wilt symptoms of tomato (Lycopersicon esculentum Mill.) plants were found in two commercial greenhouses in the Damyang area of Korea. Approximately 1% of 7,000 to 8,000 tomato plants were wilted and chlorotic in each greenhouse. The vascular tissue was usually dark brown and the discoloration extended to the apex. Fragments (each 5 × 5 mm) of the symptomatic tissue were surface-sterilized with 1% NaOCl for 1 min, then rinsed twice in sterilized distilled water (SDW). The tissue pieces were placed on water agar and incubated at 25°C for 4 to 6 days. Nine Fusarium isolates were obtained from four diseased plants, of which three isolates were identified as F. oxysporum based on morphological characteristics on carnation leaf agar medium and DNA sequences of the translation elongation factor 1-alpha (EF-1α) gene (2). Macroconidia were mostly 3- to 5-septate, slightly curved, and 28 to 53 × 2.8 to 5.2 μm. Microconidia were abundant, borne in false heads or short monophialides, generally single-celled, oval to kidney shaped, and 5 to 23 × 3 to 5 μm. Chlamydospores were single or in short chains. The EF-1α gene was amplified from three isolates by PCR assay using ef1 and ef2 primers (3), and the amplification products were sequenced. The nucleotide sequences obtained were deposited in GenBank (Accession Nos. KC491844, KC491845, and KC491846). BLASTn analysis showed 99% homology with the EF-1α sequence of F. oxysporum f. sp. lycopersici MN-24 (HM057331). Pathogenicity tests and race determination were conducted using root-dip inoculation (4) on seedlings of tomato differential cultivars: Ponderosa (susceptible to all races), Momotaro (resistant to race 1), Walter (resistant to races 1 and 2), and I3R-1 (resistant to all races). A spore suspension was prepared by flooding 5-day-old cultures on potato dextrose agar with SDW. Plants at the first true-leaf stage were inoculated by dipping the roots in the spore suspension (1 × 106 conidia/ml) for 10 min. Inoculated plants were transplanted into pots containing sterilized soil, and maintained in the greenhouse at 25/20°C (12/12 h). Twenty-four seedlings of each cultivar were arranged into three replications. An equal number of plants of each cultivar dipped in water were used as control treatments. Disease reaction was evaluated 3 weeks after inoculation, using a disease index on a scale of 0 to 4 (0 = no symptoms, 1 = slightly swollen and/or bent hypocotyl, 2 = one or two brown vascular bundles in the hypocotyl, 3 = at least two brown vascular bundles and growth distortion, 4 = all vascular bundles brown and the plant either dead or very small and wilted). All isolates caused symptoms of fusarium wilt on all cultivars except I3R-1, indicating that the isolates were race 3. The pathogen was reisolated from the discolored vascular tissue of symptomatic plants. Control plants remained asymptomatic, and the pathogen was not reisolated from the vascular tissue. Fusarium wilt of tomato caused by isolates of F. oxysporum f. sp. lycopersici races 1 and 2 has been reported previously; however, race 3 has not been reported in Korea (1). To our knowledge, this is the first report of isolates of F. oxysporum f. sp. lycopersici race 3 on tomato in Korea. References: (1) O. S. Hur et al. Res. Plant Dis. 18:304, 2012 (in Korean). (2) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Ames, IA, 2006. (3) K. O'Donnell et al. Proc. Nat. Acad. Sci. 95:2044, 1998. (4) M. Rep et al. Mol. Microbiol. 53:1373, 2004.

scholarly journals American Ginseng Root Rot Caused by Fusarium redolens in China

Plant Disease ◽  
2021 ◽  
Author(s):  
Sanhong Fan ◽  
Fangjie Zhao ◽  
Jiguang Zhang ◽  
Wenjing Shang ◽  
Xiaoping Hu
Keyword(s):  
Root Rot ◽  
Vascular Tissue ◽  
Morphological Characteristics ◽  
American Ginseng ◽  
Shaanxi Province ◽  
Ginseng Root ◽  
Continuous Cropping ◽  
Sterile Water ◽  
Fusarium Spp ◽  
Fusarium Redolens

American ginseng (Panax quinquefolium L.) originating from North America is one of important herbal medicine and economic crops . With the increasing market demand, China has become the third producer and the largest consumer country of American ginseng. However, continuous cropping obstacle has become the most serious problem for the production of American ginseng, and the continuous cropping of soils usually lead to accumulations of root fungal pathogens and increasing plant disease occurrence (1), root rot caused by the notorious soil-borne pathogenic fungi, Fusarium spp., results in a significant reduction of yield and quality of American ginseng. Investigation of American ginseng root rot was carried out in Liuba county, Shaanxi province, China from 2017 to 2019. About 20% of over 3-year-old American ginseng showed varied root rot symptoms in newly reclaimed fields, and more than 70% in continuous American ginseng planting fields. Among these root rot diseases, we found one kind of disease which shows symptoms of red leaves in initial stage and yellow or yellow brown lesions at the reed heads or taproots. The lesions mainly appear on the root surface; however, the vascular tissue has no discoloration. The aboveground parts become wilted and died, and the whole root appears dark brown rots. Fifteen Fusarium spp. isolates were obtained by cutting diseased rot roots into 5 × 5 mm2 pieces, disinfecting in 70% ethanol for 1 min, rinsing 2 ~ 3 times in sterile water for 1 min and isolating on PDA medium including 50 μg/mL streptomycin sulfate. All the isolates have identical morphological characteristics. The colony was white with curved and uplifted aerial hyphae in central region. The colony diameter was 48 ~51 mm after 6 days at room temperature. Microconidia were oval to cylindrical shape with 0 to 1 septa, ranged from 6.24 to10.09 μm long; the macroconidia were fusiform to conical with a hooked apical cell and a foot-shaped basal cell, usually 3 to 5 septa, ranged from 31.45 to 42.52 μm long. The chlamydospores were not found under our culture condition. Preliminary data analysis showed that the morphological characteristics of these isolates were consistent with the descriptions of Fusarium redolens (2). To clarify the fungus in the taxonomy , the rDNA internal transcribed spacer (ITS), the translation elongation factor 1 alpha (TEF1-α) and the RNA polymerase II subunit 1 (RPB1) fragments of two randomly selected isolates were amplified and sequenced. The sequences of the corresponding fragments of the two isolates were identical. The blast results in the GenBank and FUSARIUM-ID databases show the isolates belong to F. redolens (3). Previous study indicated F. redolens has an indistinguishable relative, F. hostae (4). Although the ITS sequence (MW331695) cannot provide enough information to distinguish them, the phylogenetic tree combined the sequence of TEF1-α (tempID: 2407237 ) and RPB1 (tempID: 2407229) clearly showed that the isolates are F. redolens. (Fig) The pathogenicity of a representative isolate, YP04, was tested on ginseng taproot by in vivo inoculation experiments with three replications. The taproot surface of 2-year-old healthy ginseng was washed and disinfested with 75% alcohol for 1 min and rinsed with sterile water, and dried. The surface of taproot was injured with sterilized steel needles and immersed in 1 × 106 /ml spore suspension (sterile water for control plants) for 30 min. The treatment and control plants were transplanted in 20 cm diameter flowerpots filled with sterilized humus and cultured in a greenhouse at 18-23°C. Six days after transplanting, the leaves began to turn red. The cortex of ginseng taproot showed yellow brown lesions and the vascular tissue turn to light yellow. Fifteen days after transplanting, the aboveground parts of treatment plants began to wilting and the taproots showed serious rots. no taproot rot was observed in the controls. The pathogen was re-isolated from the diseased taproots successfully. To our knowledge, this is the first report of F. redolens causing root rot of American ginseng in China.

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