First Report of Root Rot of Soybeans Caused by Corynespora cassiicola in Wisconsin

Corynespora cassiicola (Berk. & M. A. Curtis) C. T. Wei was isolated from diseased soybean plants (Glycine max) collected in two fields near Racine and Arlington, WI. Plants sampled at seedling emergence (VC), late vegetative (V5), and mid-reproductive (R5) stages exhibited reddish to dark brown longitudinal lesions on the exterior of the tap root extending vertically on the hypocotyl to the soil line, and extensive necrosis of lateral roots. Sample size at each growth stage was 144 plants per site. Roots were surface sterilized in 0.5% sodium hypochlorite for 2 min and sections of symptomatic tissue placed on water agar (12 g/liter) containing 100 μg of streptomycin per ml. Sporulation occurred on lesions and on mycelium that had grown out from the plant tissue onto the water agar following a 2-week incubation at 24°C under fluorescent light (280 μmol s-1 m-2). Incidence of isolation of C. cassiicola at both sites was 40% of plants sampled at growth stage VC, 67% at V5, and 78% at R5. Conidia characteristic of C. cassiicola were particularly abundant on the surface of necrotic lateral root tissue. Elongated conidia produced on water agar were 151 ± 5 μm × 15 ± 0.5 μm with an average of 13 ± 0.4 cells separated by hyaline pseudosepta (1). To confirm pathogenicity, a 1-cm lateral slice into each of four 5-day-old soybean seedling roots was made and a plug of agar taken from the margin of a colony of C. cassiicola grown on potato dextrose agar was placed in each wound and incubated for 14 days at 24°C in a growth chamber. Symptoms similar to those of diseased field plants were observed and C. cassiicola was reisolated from all plants inoculated with C. cassiicola; all controls treated with agar alone had no symptoms and C. cassiicola was recovered from none of the noninoculated controls. This is the first report of root rot caused by C. cassiicola on soybean in Wisconsin. Reference: (1) W. L. Seaman and R. A. Shoemaker. Can. J. Bot. 43:1461, 1965.

Download Full-text

First Report of Pythium Root Rot of Rau Ram (Polygonum odoratum)

Plant Disease ◽

10.1094/pd-89-0340a ◽

2005 ◽

Vol 89 (3) ◽

pp. 340-340

Author(s):

E. N. Rosskopf ◽

C. B. Yandoc ◽

B. Stange ◽

E. M. Lamb ◽

D. J. Mitchell

Keyword(s):

Root Rot ◽

Vascular System ◽

Pond Water ◽

Centraalbureau Voor ◽

First Report ◽

Pathogenicity Tests ◽

Symptomatic Tissue ◽

Pythium Helicoides ◽

Production House ◽

Test Plants

Polygonum odoratum (= Persicaria odorata), known as rau ram or sang hum, is native to southeastern Asia and is a common herb in Vietnamese cuisine (1). It has been studied most extensively for its aromatic compound content (2). In Florida, rau ram commonly is grown hydroponically in greenhouses using large, cement beds with recirculated water. The plants form dense mats from which new growth is trimmed for market. During January of 2002, a severe dieback was observed in one production house in Saint Lucie County, FL. Plants with less severe symptoms were yellowed and stunted. Roots of symptomatic plants were largely decayed with root symptoms beginning as a tip necrosis. The cortex of severely affected roots slipped off easily, leaving a stringy vascular system. Plating of symptomatic tissue from 20 randomly selected plant samples was performed with multiple general and selective media including potato dextrose agar, corn meal agar with pimaricin, ampicillin, rifampicin, and pentachloronitrobenzene (PARP) (3). All colonies produced were identified as Pythium helicoides Drechsler on the basis of sporangial, oogonial, and antheridial characteristics (4). Isolates had proliferous, obovoid, papillate sporangia, and were homothallic with smooth-walled oogonia and thick-walled, aplerotic oospores. Multiple antheridial attachments per oogonium were common with the antheridium attached along its entire length. Pathogenicity tests were conducted using P. odoratum plants grown from commercial transplants. Two tests were performed. Each test was conducted using eight inoculated and eight control plants. In the first test, plants were maintained in 10-cm pots immersed in sterilized pond water for the duration of the test. Plants were inoculated with five 7- × 70-mm sections of freshly growing mycelial culture per plant using 10-day-old cultures of Pythium helicoides grown on water agar. Chlorosis was observed at approximately 2 months after inoculation. Root necrosis was observed in inoculated plants approximately 5 months after inoculation. This test was performed in the greenhouse with temperatures ranging from 20 to 30°C. The second test was performed in growth chambers at 35 to 40°C. Plants were maintained in 10-cm pots immersed in Hoagland's solution and were inoculated with four 6-mm plugs per plant. Symptoms were observed on inoculated plants at this temperature within 1 week of inoculation. No chlorosis or root decay was observed in noninoculated, immersed plants. The pathogen was reisolated from inoculated, symptomatic tissue. To our knowledge, this is the first report of root rot of P. odoratum caused by Pythium helicoides. References: (1) R. E. Bond. Herbarist 55:34, 1989. (2) N. X. Dung et al. J. Essent. Oil Res. 7:339, 1995. (3) M. E. Kannwischer and D. J. Mitchell. Phytopathology 68:1760, 1978. (4) A. J. van der Plaats-Niterink. Monograph of the Genus Pythium. Vol. 21, Studies in Mycology. Centraalbureau voor Schimmelcutltures, Baarn, The Netherlands, 1981.

Download Full-text

First Report of Crown and Root Rot Caused by Rhizoctonia solani AG-4 on Orange Jessamine in Italy

Plant Disease ◽

10.1094/pdis-93-2-0204b ◽

2009 ◽

Vol 93 (2) ◽

pp. 204-204 ◽

Cited By ~ 1

Author(s):

D. Aiello ◽

A. Vitale ◽

E. Lahoz ◽

R. Nicoletti ◽

G. Polizzi

Keyword(s):

Rhizoctonia Solani ◽

Root Rot ◽

Morphological Characteristics ◽

Ruthenium Red ◽

Fluorescent Light ◽

First Report ◽

Pectic Enzymes ◽

Electrophoretic Patterns ◽

Crown And Root Rot ◽

Hyphal Diameter

Murraya paniculata (L.) Jack, commonly called orange jessamine or orange jasmine (Rutaceae), is a small tropical tree that is native to Asia. This species, closely related to Citrus, is grown as an ornamental tree or hedge. During October of 2007, crown and root rot was observed on approximately 12,000 pot-grown, 4-month-old plants in a nursery in eastern Sicily, Italy. Basal leaves turned yellow and gradually became necrotic, and infected plants often died. Disease symptoms were observed on 1,800 (15%) plants. Isolations from affected tissues on potato dextrose agar (PDA) amended with streptomycin sulfate at 100 mg/liter recovered a fungus with mycelial and morphological characteristics consistent with Rhizoctonia solani Kühn. Fungal colonies were initially white, turned brown with age, and produced irregularly shaped, brown sclerotia. Microscopic examination revealed that hyphae had a right-angle branching pattern, were constricted at the base of the branch near the union with main hyphae, and were septate near the constriction. The nuclear condition of hyphal cells was determined on cultures grown at 25°C on 2% water agar (WA) when stained with 3% safranin O solution and examined at ×400. Anastomosis groups were determined by pairing isolates on 2% WA in petri plates (4). Pairings were made with tester strains AG-1 IA, AG-2-2-1, AG-2-2IIIB, AG-2-2IV, AG-3, AG-4, AG-5, AG-6, and AG-11. Anastomosis was observed only with tester isolates of AG-4 producing both C2 and C3 reactions. The hyphal diameter at the point of anastomosis was reduced, the anastomosis point was obvious, and cell death of adjacent cells was observed. These results were consistent with other reports on anastomosis reactions (1). The identification of group AG-4 within R. solani has been confirmed by electrophoretic patterns of pectic enzymes (polygalacturonases) in vertical pectin-acrylamide gel stained with ruthenium red (2). Pathogenicity tests were conducted on potted, healthy, 6-month-old seedlings of orange jessamine. Twenty-five plants were inoculated by placing 1-cm2 PDA plugs from 5-day-old mycelial cultures near the base of the stem. The same number of plants inoculated with PDA plugs served as controls. Plants were maintained at 25°C and 95% relative humidity on a 12-h fluorescent light/dark regimen. Wilt symptoms, identical to ones observed in the nursery, developed 3 months after inoculation because of crown and root rot. Control plants remained disease free. The pathogen was reisolated from symptomatic tissues, completing Koch's postulates. Collar rot due to R. solani was previously detected on M. koenigii (3). To our knowledge, this is the first report of R. solani causing disease on M. paniculata. References: (1) D. E. Carling. Page 37 in: Grouping in Rhizoctonia solani by Hyphal Anastomosis Reactions. Kluwer Academic Publishers, the Netherlands, 1996. (2) R. H. Cruickshank and G. C. Wade. Anal. Biochem. 107:177, 1980. (3) A. C. Jain and K. A. Mahmud. Rev. Appl. Mycol. 32:460, 1953. (4) C. C. Tu and J. W. Kimbrough. Mycologia 65:941, 1973.

Download Full-text

First Report of Pre- and Postemergence Damping-off of Cowpea Caused by Pythium ultimum in South Africa

Plant Disease ◽

10.1094/pdis.2000.84.8.922b ◽

2000 ◽

Vol 84 (8) ◽

pp. 922-922 ◽

Cited By ~ 2

Author(s):

T. A. S. Aveling ◽

A. Adandonon

Keyword(s):

South Africa ◽

Lateral Roots ◽

Seedling Emergence ◽

Soft Rot ◽

Pythium Ultimum ◽

Centraalbureau Voor ◽

First Report ◽

Soil Line ◽

Cowpea Seed ◽

Genus Pythium

During a disease survey of cowpea (Vigna unguiculata (L.) Walp.) in Southern Africa in 1999, a major problem recorded by small-holder rural farmers in areas with wet soil types was reduced seedling emergence. Nongerminated, diseased seeds in these fields were either a brown blotchy color or had a soft rot and disintegrated upon touch. Germinated seedlings failing to emerge above the soil line were characterized by water-soaked lesions girdling the hypocotyl. Emerged seedlings had necrotic taproots and few lateral roots. Infected hypocotyls above the soil line had light brown lesions, and seedlings showed symptoms of wilting. Diseased seeds and seedlings were collected, surface-sterilized, plated on 2% water agar, and Pythium ultimum was isolated. Identification was based on characteristics given in van der Plaats-Niterink (1). Sterile soilbased compost, infested by mixing with P. ultimum mycelia (10 CFU/g of compost), was used to fill 104-cell plastic seedling trays (40 × 28 × 3.5 cm). A single cowpea seed was planted at a depth of 2 cm in each cell, and trays were maintained in a greenhouse at approximately 20°C. Seeds and seedlings showed symptoms identical to those in the field 10 days after planting, and the pathogen was successfully reisolated. Seedlings in noninoculated compost remained symptomless. This is the first report of P. ultimum on cowpea in South Africa. Reference: (1) A. J. van der Plaats-Niterink. Monograph of the Genus Pythium. Centraalbureau voor Schimmelcultures, Baarn, 1981.

Download Full-text

First Report of Root Rot Caused by Binucleate Rhizoctonia Anastomosis Group F on Musa spp.

Plant Disease ◽

10.1094/pdis-08-10-0602 ◽

2011 ◽

Vol 95 (4) ◽

pp. 490-490

Author(s):

J. Yin ◽

D. Koné ◽

M. Rodriguez-Carres ◽

M. A. Cubeta ◽

L. L. Burpee ◽

...

Keyword(s):

Root Rot ◽

Lateral Roots ◽

Anastomosis Group ◽

Molecular Characteristics ◽

First Report ◽

Binucleate Rhizoctonia ◽

Musa Spp ◽

University Of Georgia ◽

Its Regions ◽

The University

A research program was initiated at the University of Georgia in 2003 to identify banana cultivars suitable for production in the coastal and southern areas of the state. During a root disease survey conducted in October 2007 on bananas (Musa spp.) grown at the University of Georgia Bamboo Farm and Coastal Gardens in Savannah, GA, root lesions and root rot were observed on banana cvs. Gold Finger, Kandarian, and Manzano. Root lesions were dark brown to black and irregular in shape, with partial or entire roots affected. Lateral roots and outer layers of cord roots (roots arising from interior layers of the corm) of infected plants were blackened and rotted. Diseased root samples were collected from three plants of each cultivar, surface sterilized with 0.6% sodium hypochlorite, and placed on tannic acid benomyl agar (TABA). Pure cultures of the fungus consistently associated with diseased tissue were obtained by subculturing hyphal tips on TABA. Mycelia of the fungus on potato dextrose agar (PDA) were light to deep brown and the hyphae tended to branch at right angles. A septum was present in each hyphal branch near the point of origin and a slight constriction at the branch was observed. The hyphae of two isolates were stained with 0.6% phenosafranin and 3% KOH and binucleate hyphal cells were observed. On the basis of these morphological features, the isolates appeared to be binucleate Rhizoctonia anamorphs (teleomorph Ceratobasidium Rogers). For molecular identification, the internal transcribed spacer (ITS) regions and the 5.8S gene from rDNA of the isolates were cloned and sequenced (GenBank Accession No. HQ168370). The ITS regions (775 bp) were 100% identical between the two isolates and 99% identical to Ceratobasidium sp. AG-F strain SIR-1 isolated from sweet potato in Japan (GenBank Accession No. AF354085). The anastomosis group of the isolates was confirmed by pairing with strain SIR-1 on PDA. On the basis of morphological and molecular characteristics and the anastomosis assay, the two isolates were identified as a Ceratobasidium sp. AG-F (1–3). Pathogenicity assays were conducted by inoculating banana plants (cv. Golden pillow, synonym = Manzano) grown in pots under greenhouse conditions (25 to 27°C). Twenty wheat seeds infested with each isolate were placed uniformly around each plant at a depth of 10 cm in the soil. The plants were incubated in the greenhouse and the roots were examined 2 months after inoculation. Brown-to-black lesions and root rot, identical to symptoms associated with field banana roots, were observed on all inoculated plants but not on the noninoculated control plants. The fungus was reisolated from affected root samples and the identity was confirmed by morphological and molecular characteristics and the anastomosis assay. To our knowledge, this is the first report of banana root rot caused by binucleate Rhizoctonia anastomosis group F. With the increased interest in producing bananas for food and ornamental purposes, the occurrence of Ceratobasidium root rot on bananas needs to be considered when designing disease management programs and searching for suitable cultivars for banana production. References: (1) L. L. Burpee et al. Mycologia 70:1281, 1978. (2) D. González et al. Mycologia 93:1138, 2001. (3) B. Sneh et al. Identification of Rhizoctonia Species. The American Phytopathological Society, St. Paul, MN. 1991.

Download Full-text

First Report of Fusarium Wilt of Lettuce Caused by Fusarium oxysporum f. sp. lactucae in Arizona

Plant Disease ◽

10.1094/pdis.2003.87.10.1265c ◽

2003 ◽

Vol 87 (10) ◽

pp. 1265-1265 ◽

Cited By ~ 23

Author(s):

M. E. Matheron ◽

S. T. Koike

Keyword(s):

Fusarium Oxysporum ◽

Root Rot ◽

The United States ◽

San Joaquin Valley ◽

Fluorescent Light ◽

Lettuce Seedling ◽

Disease Symptoms ◽

First Report ◽

Root Rot Disease ◽

Rot Disease

A new wilt and root rot disease was observed in 6 and 11 commercial fields of lettuce (Lactuca sativa) in western Arizona during the fall of 2001 and 2002, respectively. Distance between infested sites ranged from approximately 0.5 to 39 km. Five head lettuce cultivars as well as a red leaf lettuce cultivar were affected. Disease symptoms included yellowing and wilting of leaves, as well as stunting and plant death. The cortex of the crown and upper root of infected plants usually was decayed and reddish brown. Disease symptoms first appeared at the time of plant thinning and continued to develop up to plant maturity. Fusarium oxysporum was consistently isolated from symptomatic plant roots. Seeds of cv. Lighthouse were planted in nonsterile vermiculite within 3.0-cm-square × 7.0-cm-deep cells in a transplant tray and thinned to a single plant per cell. When the first true leaves were emerging, 10 individual seedlings were inoculated with a single-spore isolate of F. oxysporum recovered from diseased lettuce root cortex tissue. Inoculum was prepared by growing the fungus on potato dextrose agar in 100-mm-diameter × 15-mm-deep plastic petri dishes at 28°C with a 12-h photoperiod under fluorescent light. Once the fungus completely covered the agar surface, 50 ml of sterile distilled water was added to the dish, and the mycelia and conidia on the surface were scraped off the agar and suspended in the water. This fungal suspension was decanted, and a 2-ml aliquot containing 1.8 × 105 CFU was pipetted into the vermiculite near the stem of each lettuce seedling. Ten plants grown in noninfested vermiculite served as uninoculated controls. After inoculation, plants were maintained in a growth chamber at 28°C with a 12-h photoperiod under fluorescent light for 3 weeks. Symptoms of yellowing, wilt, vascular decay, and often plant death developed during the incubation period on all inoculated plants but not on control plants. Fusarium oxysporum was consistently reisolated from inoculated plants but not from uninoculated plants. The experiment was repeated and yielded the same results. A wilt and root rot disease of lettuce attributed to F. oxysporum f. sp. lactucae was first reported in Japan in 1967 (3) and subsequently in the United States (San Joaquin Valley of California) in 1993 (2), and Italy in 2002 (1). The researchers of the U.S. report did not cite the earlier work from Japan and described the pathogen as F. oxysporum f. sp. lactucum. The Arizona isolate used to demonstrate pathogenicity was of the same vegetative compatibility group as an isolate of the pathogen from lettuce in California reported in 1993. Several companies grow and harvest lettuce in Arizona and California. At the end of production and harvest in the fall, tractors, implements, and harvesting equipment are transported from the San Joaquin Valley in California to western Arizona. The similarity between the isolate of F. oxysporum f. sp. lactucae from western Arizona and the San Joaquin Valley of California suggest a possible introduction of the pathogen into Arizona from California, perhaps on soil adhering to farm equipment. To our knowledge, this is the first report of F. oxysporum f. sp. lactucae infecting lettuce in Arizona. References: (1) A. Garibaldi et al. Plant Dis. 86:1052, 2002. (2) J. C. Hubbard and J. S. Gerik. Plant Dis. 77:750, 1993. (3) T. Matuo and S. Motohashi. Trans. Mycol. Soc. Jpn. 8:13, 1967.

Download Full-text

First Report of Fusarium Root Rot of Stored Carrot Caused by Fusarium avenaceum in Serbia

Plant Disease ◽

10.1094/pdis-07-14-0724-pdn ◽

2015 ◽

Vol 99 (2) ◽

pp. 286-286

Author(s):

I. Stanković ◽

K. Milojević ◽

A. Vučurović ◽

D. Nikolić ◽

B. Krstić ◽

...

Keyword(s):

Root Rot ◽

Apical Cell ◽

Morphological Characteristics ◽

Fusarium Avenaceum ◽

Control Treatment ◽

Fluorescent Light ◽

Fungal Mycelium ◽

Vegetable Crops ◽

Orange Pigment ◽

First Report

Carrot (Daucus carota L. subsp. sativus (Hoffm.) Thell., Apiaceae), a widely consumed antioxidant-rich plant, is among the major vegetable crops grown in Serbia, with average annual production of 65,400 tons on approximately 7,000 ha (4). In May 2013, a severe root rot was observed on approximately 20% of cold-stored carrot roots originating from Gospođinci, South Bačka District, Serbia. Symptoms included dry rot of the collar and crown as well as large, brown to dark brown, circular, sunken lesions on the stored roots. Frequently, abundant whitish mycelium was observed covering the surface of the colonized roots. To determine the causal agent, small pieces of infected tissue were surface-disinfested with 2% NaOCl without rinsing, air-dried, and placed on potato dextrose agar. Five single-spore isolates obtained from collar and crown tissue sections, as well as nine isolates from root sections, all formed abundant, cottony white to pale salmon fungal colonies with reddish orange pigment on the reverse surface of the agar medium when grown at 25°C under 12 h of fluorescent light per day. All recovered isolates formed numerous, three- to six-septate, hyaline, needle-like, straight to slightly curved, fusoid macroconidia (30 to 80 × 4 to 5.5 μm, average 58.3 × 4.9 μm, n = 100 spores) each with a tapering apical cell. Microconidia of all isolates were generally scarce, two- to four-septate, spindle-shaped, and 15 to 35 × 3 to 5 μm (average 21.3 × 4.2 μm). Chlamydospores were not observed. Based on these morphological characteristics, the pathogen was identified as Fusarium avenaceum (Fries) Saccardo (1). The pathogenicity on carrot was tested for isolate 19-14 by inoculating each of five carrot roots surface-disinfected with 2% NaOCl, by placing a mycelial plug into the surface of a wound created with a cork borer. Carrot roots inoculated with sterilized PDA plugs served as a negative control treatment. After 5 days of incubating the roots at 25°C, root rot symptoms identical to those observed on the source carrot plants developed on all inoculated roots, and the pathogen was re-isolated from each of these roots using the same procedure descibed above. There were no symptoms on the control roots. Morphological species identification was confirmed by sequencing the translation elongation factor (EF-1α) gene (2). Total DNA was extracted directly from fungal mycelium of isolate 19-14 with a DNeasy Plant Mini Kit (Qiagen, Hilden, Germany), and PCR amplification was performed with primer pair EF-1/EF-2 (2). Sequence analysis of the EF-1α gene revealed 100% nucleotide identity of isolate 19-14 (GenBank Accession No. KM102536) with the EF-1α sequences of two F. avenaceum isolates from Canada (KC999504 from rye and JX397864 from Triticum durum). To our knowledge, this is the first report of F. avenaceum causing collar, crown, and root rots of stored carrot in Serbia. Since F. avenaceum can produce several mycotoxins, including moniliformin, acuminatopyrone, and chrysogine (3), the presence of this pathogen on stored carrots could represent a significant constraint for carrot production in Serbia, for both direct yield losses and potential mycotoxin contamination. References: (1) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual, Blackwell Publishing, London, UK, 2006. (2) K. O'Donnell et al. Proc. Natl. Acad. Sci. U.S.A. 95:2044, 1998. (3) J. L. Sorenson. J. Agric. Food Chem. 57:1632, 2009. (4) Statistical Office, Republic of Serbia. Retrieved from http://webrzs.stat.gov.rs in May 2014.

Download Full-text

First Report of Crown and Root Rot Caused by Rhizoctonia solani AG-4 on Banana Passionflower (Passiflora mollissima) in Italy

Plant Disease ◽

10.1094/pdis-05-11-0411 ◽

2011 ◽

Vol 95 (9) ◽

pp. 1194-1194 ◽

Cited By ~ 2

Author(s):

G. Polizzi ◽

D. Aiello ◽

V. Guarnaccia ◽

A. Panebianco ◽

P. T. Formica

Keyword(s):

Rhizoctonia Solani ◽

Root Rot ◽

Disease Incidence ◽

Morphological Characteristics ◽

Fluorescent Light ◽

Disease Symptoms ◽

First Report ◽

Pathogenicity Tests ◽

Crown And Root Rot ◽

Safranin O

The genus Passiflora (Passifloraceae family) contains more than 500 species and several hybrids. In Italy, some of these species and hybrids are grown as ornamental evergreen vines or shrubs. During August and September 2010, a crown and root rot was observed in a stock of approximately 6,000 potted 2-year-old plants of Passiflora mollissima (Kunth) Bailey, commonly known as the banana passionflower, in a nursery located in eastern Sicily (southern Italy). Disease incidence was approximately 20%. Disease symptoms consisted of water-soaked lesions at the crown and a root rot. Successively, older crown lesions turned light brown to brown and expanded to girdle the stem. As crown and root rot progressed, basal leaves turned yellow and gradually became necrotic and infected plants wilted and died. A fungus with mycelial and morphological characteristics of Rhizoctonia solani Kühn was consistently isolated from crown lesions and brown decaying roots when plated on potato dextrose agar (PDA) amended with streptomycin sulfate at 100 μg/ml. Fungal colonies were initially white, turned brown with age, and produced irregularly shaped, brown sclerotia. Mycelium was branched at right angles with a septum near the branch with a slight constriction at the branch base. Hyphal cells removed from 10 representative cultures grown at 25°C on 2% water agar were determined to be multinucleate when stained with 1% safranin O and 3% KOH solution (1) and examined at ×400. Anastomosis groups were determined by pairing isolates on 2% water agar in petri plates (4). Pairings were made with tester strains of AG-1, AG-2, AG-3, AG-4, AG-5, AG-6, and AG-11. Anastomosis was observed only with tester isolates of AG-4 (3). Pathogenicity tests were performed on container-grown, healthy, 3-month-old cuttings. Twenty plants of P. mollissima were inoculated near the base of the stem with five 1-cm2 PDA plugs from 5-day-old mycelial plugs obtained from two representative cultures. The same number of plants served as uninoculated controls. Plants were maintained at 25°C and 95% relative humidity with a 12-h fluorescent light/dark regimen. Wilt symptoms due to crown and root rot, identical to ones observed in the nursery, appeared 7 to 8 days after inoculation with either of the two isolates and all plants died within 20 days. No disease was observed on control plants. R. solani AG-4 was reisolated from symptomatic tissues and identified as previously described, confirming its pathogenicity. Damping-off or crown and root rot due to R. solani were previously detected on P. edulis in Brazil, Africa, India, Oceania, and Australia (2). To our knowledge, this is the first report of R. solani causing crown and root rot on P. mollissima. References: (1) R. J. Bandoni. Mycologia 71:873, 1979. (2) J. L. Bezerra and M. L. Oliveira. Fitopathol. Brasil. 9:273, 1984. (3) D. E. Carling. Page 37 in: Grouping in Rhizoctonia solani by Hyphal Anastomosis Reactions. Kluwer Academic Publishers, the Netherlands, 1996. (4) C. C. Tu and J. W. Kimbrough. Mycologia 65:941, 1973.

Download Full-text

Prevalence, pathogenicity and cultivar resistance of Fusarium and Rhizoctonia species causing soybean root rot

Canadian Journal of Plant Science ◽

10.4141/cjps2012-223 ◽

2013 ◽

Vol 93 (2) ◽

pp. 221-236 ◽

Cited By ~ 17

Author(s):

J. X. Zhang ◽

A. G. Xue ◽

E. R. Cober ◽

M. J. Morrison ◽

H. J. Zhang ◽

...

Keyword(s):

Plant Height ◽

Root Rot ◽

Seedling Emergence ◽

Dry Weight ◽

Field Resistance ◽

Adult Plant ◽

Cultivar Resistance ◽

Soybean Root ◽

Root Dry Weight ◽

Seedling Roots

Zhang, J. X., Xue, A. G., Cober, E. R., Morrison, M. J., Zhang, H. J., Zhang, S. Z. and Gregorich, E. 2013. Prevalence, pathogenicity and cultivar resistance of Fusarium and Rhizoctonia species causing soybean root rot. Can. J. Plant Sci. 93: 221–236. Root rot complex, caused by Fusarium and Rhizoctonia species, is a major soybean disease in Canada. We isolated nine Fusarium and Rhizoctonia species including F. oxysporum (Fo), F. graminearum (Fg), F. solani (Fs), F. avenaceum (Fa), F. tricinctum (Ft), F. sporotrichioides (Fsp), F. equiseti (Fe), F. poae (Fp), and R. solani (Rs) from soybean roots in eastern Ontario, Canada. The isolation results indicated that Fo was the most prevalent species while Fa, Fsp, and Fp were the least frequent species in the soybean rhizosphere. Numbers of Fo, Fs, Fg, and Rs isolates recovered from adult plant roots were significantly greater than those from seedling roots (P<0.01). The Rs, Fg and Fsp isolates were significantly more abundant in the no-till field than in the tilled field (P<0.01). Based on the greenhouse assays, Rs, Fg, and Fa were the most pathogenic species, while Fe and Fsp were the least pathogenic to soybean. The field resistance evaluation, based on the root rot severity, identified 21, 17, 30, and 3 out of 70 cultivars among the most tolerant to Fg, Fo, Fs, and Rs, respectively. A few of the cultivars showed partial resistance to multiple species, based on root rot severity and reduction in their seedling emergence, plant height, and root dry weight, but no cultivar was found to partially resist all four species. There was no correlation (P>0.05) between root rot severity and the reduction in seedling emergence, plant height, or root dry weight.

Download Full-text

First Report of Rhizoctonia solani Causing a Disease of Sunflower in India

Plant Disease ◽

10.1094/pdis-94-4-0488c ◽

2010 ◽

Vol 94 (4) ◽

pp. 488-488 ◽

Cited By ~ 5

Author(s):

K. Srinivasan ◽

S. Visalakchi

Keyword(s):

Rhizoctonia Solani ◽

Root Rot ◽

Crown Rot ◽

Pathogenicity Test ◽

American Phytopathological Society ◽

First Report ◽

Leaf Yellowing ◽

Crown Tissue ◽

Symptomatic Tissue ◽

White Mycelium

During the spring of 2009, symptoms including leaf yellowing and wilting, root rot, and death of plants were noted in sunflower (Helianthus annuus L.) crops in Dharmapuri District, Tamilnadu, India. In some fields, approximately 30% of the plants were affected. The disease began when plants were approximately 10 weeks old and occurred on scattered or adjacent plants. The presence of white mycelium was observed on necrotic crowns. Symptomatic tissue was surface disinfested in 70% alcohol for 30 s and 0.5% sodium hypochlorite for 1 min and plated onto potato dextrose agar (PDA) (1). One isolate (coded SV001) had near right-angle branching with basal constriction and adjacent septa and sclerotia typical of Rhizoctonia spp. (2). Cream-colored colonies produced irregular, light brown sclerotia that were 3.0 to 7.3 mm (average 3.8 mm) in diameter. Hyphae were 6.8 to 7.0 μm (average 6.9 μm) wide and multinucleate (8 to 15 nuclei per cell). On the basis of hyphal anastomosis with several known AG testers, the fungus was characterized as Rhizoctonia solani Kühn AG-IV (3). One culture was deposited at the Madras University Botany Laboratory, Center for Advanced Studies in Botany, University of Madras, Chennai, India. In a pathogenicity test, R. solani SV001 was grown on PDA for 5 days at 24°C in the dark. Five-millimeter-diameter disks were placed at the base of sunflower plants (cv. Mordan). Four sunflower plants in each of three pots were inoculated; noninoculated plants served as controls. Plants were placed in a glasshouse maintained at 25 to 27°C. Inoculated plants developed yellow foliage and crown rot and root rot symptoms after 7 to 12 days and died in 17 to 20 days. No symptoms were observed on noninoculated plants. The pathogen was reisolated from fragments of necrotic crown tissue of inoculated plants. To our knowledge, this is the first report of R. solani AG-IV causing a disease of sunflower plants in India. References: (1). R. C. Fenille et al. Plant Pathol. 54:325, 2005. (2). J. R. Parmeter et al. Phytopathology 59:1270, 1969. (3) B. Sneh et al. Identification of Rhizoctonia Species. The American Phytopathological Society, St Paul, MN, 1991.

Download Full-text

First Report of Petunia Root Rot Caused by Rhizoctonia solani in Argentina

Plant Disease ◽

10.1094/pdis.2004.88.1.86b ◽

2004 ◽

Vol 88 (1) ◽

pp. 86-86

Author(s):

E. R. Wright ◽

M. C. Rivera ◽

K. Asciutto ◽

L. Gasoni ◽

V. Barrera ◽

...

Keyword(s):

Rhizoctonia Solani ◽

Root Rot ◽

Disease Incidence ◽

Common Garden ◽

Anastomosis Group ◽

Fluorescent Light ◽

First Report ◽

Blue Solution ◽

Crown And Root Rot ◽

Species Taxonomy

Common garden petunias (Petunia × hybrida Hort. Vilm.-Andr.) are herbaceous annual plants with brightly colored flowers up to 10 cm in diameter. During the winter of 2002, crown and root rot were observed on plants (cv. Ultra) growing in five greenhouses in Buenos Aires. Affected plants were randomly distributed in the greenhouses, and mean disease incidence in all the greenhouses was 26%. Basal leaves turned yellow and gradually became necrotic, and infected plants were often killed. Small pieces of affected tissues were disinfested in 2% sodium hypochlorite for 1 min and plated on 2% potato dextrose agar (PDA). Fifteen isolates identified to the genus Rhizoctonia were obtained. Fungal colonies were initially white, turned brown with age, and produced irregularly shaped, brown sclerotia. Hyphal branched at right angles, were constricted at the base of the branch near the union with main hyphae, and septate near the constriction. Basidia were not observed in the greenhouses or on the plates. Isolates were cultivated on water agar and incubated at 25°C for 3 days. Hyphal cells were determined to be multinucleate when stained with 1% aniline blue solution (2) and examined at ×400. Anastomosis group of one isolate was determined by using AG-4 HG II, AG-1 IA, AG-1 IB, AG-1 IC, AG-2 2-1, and AG-2 2IIIB tester strains of Rhizoctonia solani that includes isolates reported to be pathogenic on ornamentals (1). Anastomosis was observed only with strains of AG-4 HG II. Pathogenicity on this isolate was conducted on potted, healthy, adult plants that were 10 to 22 cm high and flowering. Thirty-five plants were inoculated by placing 1 cm2 pieces of PDA from 7-day-old mycelial cultures near the base of the stem. Twelve control plants were treated with 1 cm2 PDA plugs. Plants were kept at 22 to 24°C, >95% relative humidity, and 12 h of fluorescent light. Wilt symptoms due to basal stem rot appeared 7 days after inoculation, and all the inoculated plants died within 27 days. Control plants remained disease free. The pathogen was reisolated from symptomatic tissues, completing Koch's postulates. To our knowledge, this is the first report of R. solani causing disease on petunia in Argentina. References: (1) D. M. Benson and D. K. Cartwright. Ornamental diseases incited by Rhizoctonia spp. Pages 303–314 in: Rhizoctonia species: Taxonomy, Molecular Biology, Ecology, Pathology and Disease Control. B. Sneh et al., eds. Kluwer Academic Publishers, London, England, 1996. (2) C. C. Tu and J. W. Kimbrough. Mycologia 65:941, 1973.

Download Full-text