scholarly journals First Report of Soybean Seedling Disease caused by Rhizoctonia solani AG-7 in Taiwan

Plant Disease ◽  
2021 ◽  
Author(s):  
Yu-Cheng Lin ◽  
Min-Nan Tseng ◽  
Hao-Xun Chang
Keyword(s):  
Rhizoctonia Solani ◽  
Tap Water ◽  
Disease Incidence ◽  
Soil Surface ◽  
Anastomosis Group ◽  
Damping Off ◽  
Soybean Seedlings ◽  
Fungal Inoculum ◽  
Potential Pathogen ◽  
Causal Pathogen

From August to November 2020, reduced emergence and damping-off of soybean seedlings were observed in two fields (Benzhou and Wandan) in Taiwan. Disease incidence was approximately 40% in Benzhou by field scouting. The roots of damping-off seedlings were brown. Affected seedlings could be easily pulled out from the soil and the lesions on the roots/stem were generally dry and sunken. These symptoms suggested the possibility of Rhizoctonia infection. Soil surrounding symptomatic seedlings were collected to bait the potential pathogen and symptomatic plants were used for pathogen isolation. The diseased tissues were washed with tap water and surface-disinfected with 1% bleach before placing on the Dexon selection medium at 26°C for 2 days (Ko and Hora 1971). Hyphae were transferred to potato dextrose agar (PDA), and a brown colony with brown and irregular-shaped sclerotia grew from 90 out of 99 isolates. The hyphae exhibited typical characteristics of Rhizoctonia solani, including a constriction and a septum near the end of branching hyphae (Ajayi-Oyetunde and Bradely, 2018). Two isolates from Benzhou and two isolates from Wandan were tested for their pathogenicity, and eight surface-disinfected seeds were distributed evenly on the water agar plates covered by 2-day-old mycelia at 25°C in dark for 7 days. All isolates caused cotyledon rot and reduced germination. To verify their pathogenicity in pots, double-sterilized sorghum seeds were inoculated with two strains and incubated at 25°C for 2 weeks to be used as fungal inoculum (Ajayi-Oyetunde and Bradely, 2017). A layer of 15 ml of fungal inoculum was placed 5 cm beneath the soil surface in pots. Four soybean seeds were planted approximately 3 cm above the inoculum in each pot. After two weeks, reddish lesions on the hypocotyls or taproots of all seedlings in the inoculated pots were observed, while seedlings in the control pots inoculated with sterile sorghum seeds remained healthy. The pathogen was re-isolated from lesions and had identical morphology to the original isolates. To characterize the fungal identity, the internal transcribed spacer (ITS) was sequenced using the primers ITS1/ITS4 (Sharon et al., 2006). Using BLASTN in the NCBI database, the sequence (GenBank no. MW410857 and MW410858) showed 100% (639/639 bp) similarity to KF907734 and 99.83% (635/636 bp) similarity to AF354099, both belong to R. solani anastomosis group 7 (AG-7) (Hua et al. 2014; Gonzalez et al. 2001). Phylogenetic analysis comparing sequences with different AGs (Ajayi-Oyetunde and Bradely, 2017) grouped our isolates within the AG-7 clade with a 100% bootstrap confidence. In the anastomosis test, an incompatible zonation and unequal mycelial growth rates were observed when AG-7 isolates were paired with an AG-1 IA isolate. On the other hand, the compatible tuft reaction was observed when two AG-7 isolates were paired, and the compatible merge reaction was observed in the self-pairing tests (Macnish et al. 1997). Accordingly, the molecular and morphological characterizations confirmed the causal pathogen as R. solani AG-7. R. solani AG-7 was first reported on radishes in Japan (Homma et al., 1983), first found on carnation in Taiwan (Lo et al., 1990), and in field soils of various crops but not soybean (Chuang, 1997). It was suggested that Rhizoctonia diseases of soybean may be present in Taiwan, but molecular confirmation was lacking (Anonymus, 1979). As R. solani AG-7 causes diseases of soybean in the US and Japan (Baird et al., 1996), the importance of AG-7 as an endemic pathogen of soybean in Taiwan should be recognized and its prevalence determined as a first step to managing this disease.

scholarly journals First Report of Damping-Off Caused by Rhizoctonia solani AG-4 on Mediterranean Fan Palm in Italy

Plant Disease ◽  
2010 ◽  
Vol 94 (1) ◽  
pp. 125-125 ◽  
Author(s):  
G. Polizzi ◽  
D. Aiello ◽  
I. Castello ◽  
V. Guarnaccia ◽  
A. Vitale
Keyword(s):  
Rhizoctonia Solani ◽  
Disease Incidence ◽  
Morphological Characteristics ◽  
Mediterranean Area ◽  
Western Mediterranean ◽  
Fluorescent Light ◽  
Damping Off ◽  
Centraalbureau Voor ◽  
First Report ◽  
Stem Lesions

Mediterranean fan palm (Chamaerops humilis L.), one of just two autochthonous European palms, is native to the western Mediterranean Region in southwestern Europe and northwestern Africa. It can be found growing wild in the Mediterranean area. In Europe, this species is very popular as an ornamental plant. In March 2009, a widespread damping-off was observed in a stock of approximately 30,000 potted 1-month-old plants of C. humilis cv. Vulcano in a nursery in eastern Sicily. Disease incidence was approximately 20%. Disease symptoms consisted of lesions at the seedling shoot (plumule). Stem lesions were initially orange, turned brown, and followed by death of the entire plumule or eophyll. A fungus with mycelial and morphological characteristics of Rhizoctonia solani Kühn was consistently isolated from lesions 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 and a slight constriction at the branch base. Hyphal cells removed from 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 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 on 2% water agar in petri plates (3). Anastomosis was observed only with tester isolates of AG-4, giving both C2 and C3 reactions (2). One representative isolate obtained from symptomatic tissues was deposited at the Fungal Biodiversity Centre, Centraalbureau voor Schimmelcultures (CBS No. 125095). Pathogenicity tests were performed on container-grown, healthy, 1-month-old seedlings. Twenty plants of C. humilis cv. Vulcano were inoculated near the base of the stem with two 1-cm2 PDA plugs from 5-day-old mycelial cultures. The same number of plants served as uninoculated controls. Plants were incubated in a growth chamber and maintained at 25°C and 95% relative humidity on a 12-h fluorescent light/dark regimen. Symptoms identical to those observed in the nursery appeared 5 days after inoculation and all plants died within 20 days. No disease was observed on control plants. A fungus identical in culture morphology to R. solani AG-4 was consistently reisolated from symptomatic tissues, confirming its pathogenicity. To our knowledge, this is the first report in the world of R. solani causing damping-off on Mediterranean fan palm. References: (1) R. J. Bandoni. Mycologia 71:873, 1979. (2) D. E. Carling. Page 37 in: Grouping in Rhizoctonia solani by Hyphal Anastomosis Reactions. Kluwer Academic Publishers, the Netherlands, 1996. (3) C. C. Tu and J. W. Kimbrough. Mycologia 65:941, 1973.

Relationship of Rhizoctonia solani inoculum density to incidence of hypocotyl rot and damping-off in dry beans

1989 ◽  
Vol 35 (12) ◽  
pp. 1132-1140 ◽  
Author(s):  
A. J. L. Phillips
Keyword(s):  
Phaseolus Vulgaris ◽  
Linear Regression ◽  
Rhizoctonia Solani ◽  
Disease Incidence ◽  
Inoculum Density ◽  
Damping Off ◽  
Dry Beans ◽  
Site Model ◽  
Relationship Of

The effect of inoculum density on preemergence disease incidence was described by linear regression. Variations in virulence among 10 isolates formed a continuum. The effect of inoculum density on hypocotyl disease incidence was described by a limiting site model and variations in virulence among the isolates also formed a continuum. The ability of an isolate to cause preemergence disease was not necessarily related to its ability to cause hypocotyl disease. Both saprophytic colonization and preemergence infection arose from propagules in the spermosphere, while depending on the isolate, infection of hypocotyls was from propagules in either the rhizosphere or the rhizoplane. The observed number of hypocotyl lesions was greater than that estimated from the percentage of plants infected. This effect was more pronounced when seeds were sown at 4 than at 1 cm depth.Key words: beans, epidemiology, Phaseolus vulgaris, Rhizoctonia solani.

scholarly journals Rhizoctonia solani Anastomosis Group 3 is Predominant in Potato Tubers in Poland

Plant Disease ◽  
2013 ◽  
Vol 97 (9) ◽  
pp. 1245-1245 ◽  
Author(s):  
J. W. Woodhall ◽  
B. Lutomirska ◽  
J. C. Peters ◽  
P. S. Wharton
Keyword(s):  
Rhizoctonia Solani ◽  
Tap Water ◽  
Anastomosis Group ◽  
Black Scurf ◽  
Crop Rotations ◽  
Potato Tubers ◽  
Hyphal Fusion ◽  
Group 3 ◽  
Plant Pathol ◽  
Potato Crops

Rhizoctonia solani is a species complex of 13 related but genetically distinct anastomosis groups (AGs). In potato, R. solani can infect the stems, stolons, and roots, resulting in quantitative losses. It can also cause qualitative losses through blemishes occurring on progeny tubers, such as black scurf and elephant hide (corky cracking). Knowledge of the AG in local populations is important because they differ in host range, fungicide sensitivity, and disease severity (2). To determine the AGs present in Poland, 54 tuber samples displaying typical R. solani symptoms were taken from six different fields in 2011. The fields were representative of five different administrative regions of Poland and from at least 10 different varieties. Rhizoctonia was isolated from tubers by placing symptomatic material on to tap water agar amended with streptomycin and penicillin and after 2 to 3 days Rhizoctonia colonies were identified and hyphal tips of these transferred to potato dextrose agar. Rhizoctonia was successfully isolated from 48 tubers displaying black scurf and two tubers displaying elephant hide symptoms. DNA was extracted from Rhizoctonia cultures using a Wizard Food kit (Promega) and the AG was determined using specific real-time PCR assays (1). All Rhizoctonia isolates were determined to be AG3 and this was confirmed for 10 selected isolates by observing hyphal fusion with a known AG3 tester isolate (Rs08) as described previously (3). Pairings were also conducted amongst the 10 Polish isolates, C2 reactions were typically observed indicating numerous vegetative compatible groups are present. This study shows that AG3 is likely to be the predominant AG in potato tubers in Poland. This is similar to other studies in Europe, which have all determined that AG3 accounts for at least 92% of isolates from potato (2,3). AG2-1, 4, and 5 have also been found in tubers worldwide and climate and certain crop rotations can influence the presence of these other AGs in potato tubers (2). However, climate and crop rotations in Poland are similar to other parts of Europe so the predominance of AG3 is expected. AG3 was also isolated from elephant hide symptoms; however, it was more frequently isolated from sclerotia. The ability of AG3 to prolifically produce sclerotia and thereby survive on seed tubers may explain its predominance in potato crops (4). Therefore, studies focusing on the management of Rhizoctonia potato disease in Poland should consider AG3 in the first instance. References: (1) G. E. Budge et al. Plant Pathol. 58:1071, 2009. (2) L. Tsror. J. Phytopathol. 158:649, 2010. (3) J. W. Woodhall et al. Plant Pathol. 56:286, 2007. (4) J. W. Woodhall et al. Plant Pathol. 57:5, 2008.

scholarly journals Controlling Rhizoctonia Damping-off of Chinese Mustard by Using Endomycorrhizal Rhizoctonia spp. Isolated from Orchid Mycorrhizae

Plant Disease ◽  
2016 ◽  
Vol 100 (1) ◽  
pp. 85-91 ◽  
Author(s):  
Jr-Hau Jiang ◽  
Si-Loi Tam ◽  
Takeshi Toda ◽  
Lung-Chung Chen
Keyword(s):  
Phylogenetic Analysis ◽  
Rhizoctonia Solani ◽  
Disease Severity ◽  
Anastomosis Group ◽  
Effective Strategy ◽  
Damping Off ◽  
Binucleate Rhizoctonia ◽  
Orchid Mycorrhizae ◽  
Almost All ◽  
Test Plants

Inoculation of hypovirulent Rhizoctonia spp. has been recognized as an effective strategy for protecting plants against damping-off caused by pathogenic Rhizoctonia spp. In this study, endomycorrhizal Rhizoctonia spp. isolated from fungal pelotons in orchid plants were used for controlling Rhizoctonia damping-off of Chinese mustard. According to phylogenetic analysis and anastomosis group (AG) determination, the virulence of three isolates of multinucleate Rhizoctonia solani in AG-6; eight isolates of binucleate Rhizoctonia in AG-A, AG-B, AG-G, AG-P, and AG-R; and two isolates of binucleate R. repens were evaluated using test plants. All isolates, except that in AG-R, caused low disease severity in 10-day-old radish (0.10 to 0.61), cucumber (0.28 to 0.54), and Chinese mustard (0.18 to 0.65). By contrast, pathogenic isolates in AG-4 killed almost all test plants with symptoms of collapsed hypocotyl and wilted leaves (0.88 to 0.96). Of the 13 endomycorrhizal Rhizoctonia isolates assessed, AG-P isolates Cno10-3 and CalS1-2 provided 91 and 100% protection, respectively, against R. solani AG-4 in 26-day-old Chinese mustard. This study revealed that endomycorrhizal Rhizoctonia spp. in orchid have the potential to biologically control damping-off of Chinese mustard.

scholarly journals First report of collar and root rot of faba bean caused by Rhizoctonia solani AG-2-2 IIIB in Bangladesh

Plant Disease ◽  
2021 ◽  
Author(s):  
S. K. Paul ◽  
Dipali Rani Gupta ◽  
Nur Uddin Mahmud ◽  
A.N.M. Muzahid ◽  
Tofazzal Islam
Keyword(s):  
Rhizoctonia Solani ◽  
Faba Bean ◽  
Root Rot ◽  
Disease Incidence ◽  
Management Strategies ◽  
Its Region ◽  
Anastomosis Group ◽  
Grain Legume ◽  
Collar And Root Rot ◽  
Wheat Kernels

Faba bean (Vicia faba L.) is an underutilized promising grain legume commercially grown in central and northern part of Bangladesh (Yasmin et al. 2020). In January 2021, faba bean plants exhibiting symptoms of collar and root rot and yellowing of leaves were observed in thirty plots of an experimental field at the Bangladesh Agricultural University (24.75° N, 90.50° E), Mymensingh, Bangladesh. Infected plants had dark brown to black lesions on the roots, extending above the collar region. An average disease incidence and severity was 7.16% and 6.91%, respectively. Eight diseased plants were collected from the field by uprooting one plant from each of eight randomly selected experimental plots and surface disinfected with sodium hypochlorite (0.2%) for 3 min followed by 1 min in ethanol (70%), and then rinsed three times with distilled water and dried on sterile paper towels. Collar and root pieces (5×5 mm) of symptomatic tissues were placed on Potato Dextrose Agar (PDA). Plates were incubated at 25°C for three days and isolates were purified from single-tip culture. The isolates produced brown colored mycelia often with brown sclerotia. Under microscope, fungal colonies exhibited right–angled branching with constriction at the base of hyphal branches and a septum near the originating point of hyphal branch consistent with the description of Rhizoctonia solani Kuhn (Sneh et al. 1991). The isolates grew at 35°C on PDA (5 mm/24). Molecular identification of the isolates BTRFB1 and BTRFB7 was determined by sequencing the rDNA internal transcribed spacer (ITS) region using primers ITS1 and ITS4 (White et al. 1990). A BLAST search showed that the sequences (GenBank Accession nos. MZ158299.1 and MZ158298.1) had 99.28% similarity with R. solani isolates Y1063 and SX-RSD1 (GenBank Accession nos. JX913811.1 and KC413984.1, respectively). Phylogenetic analysis revealed that the present isolates grouped with R. solani anastomosis group AG-2-2 IIIB. To confirm pathogenicity, both isolates were grown individually on sterile wheat kernels at 28°C for 6 days (D’aes et al. 2011). Faba bean seedlings were grown in plastic pots containing sterile potting mix (field soil/composted manure/sand 2:2:1 [v/v]). Two-week-old plants were inoculated by placing five infested wheat seeds adjacent to the roots. Control pots were inoculated with sterile wheat kernels using the same procedure. Plants were placed in a growth room with a 16 h/8 h light/dark photoperiod at 25 ± 2°C after inoculation. Fifteen days after inoculation, typical collar and root rot symptoms were developed on inoculated plants, similar to symptoms observed in the field. Control plants remained non-symptomatic. Finally, six isolates of R. solani were isolated from the symptomatic plants and identified by morphological and molecular analysis. Rhizoctonia solani is the causal agent of seed and root rot, hypocotyl canker, and seedling damping-off diseases of faba bean in many other countries (Rashid and Bernier 1993; Assunção et al. 2011). To our knowledge, this is the first confirmed report of Rhizoctonia solani causing collar and root rot of faba bean in Bangladesh. This finding will be helpful for the development of management strategies to control this disease and to expand the production of faba bean in Bangladesh.

scholarly journals Binucleate Rhizoctonia on Tobacco in Zimbabwe

Plant Disease ◽  
1998 ◽  
Vol 82 (2) ◽  
pp. 263-263 ◽  
Author(s):  
A. J. Masuka
Keyword(s):  
Leaf Spot ◽  
Rating Scale ◽  
Disease Incidence ◽  
Block Design ◽  
Stem Rot ◽  
Damping Off ◽  
Binucleate Rhizoctonia ◽  
Tobacco Seedlings ◽  
Disease Rating ◽  
Causal Pathogen

Rhizoctonia solani Kühn (teleomorph Thanatephorus cucumeris (A. B. Frank) Donk) anastomosis groups AG 4 and AG 3 cause, respectively, widespread stem rot and leaf spot diseases of tobacco in Zimbabwe (2). Stem rot leads to substantial field losses, necessitating routine chemical and biological control (1). A recent increase in reports on Rhizoctonia-induced damping-off in tobacco seedlings and lodging of mature field plants prompted detailed studies on the causal pathogen. Nuclear fluorescence microscopy studies of 83 isolates from diseased tobacco revealed the presence of binucleate isolates. The isolates were collected in 1981 (1 isolate), 1990 (1 isolate), 1996 (3 isolates), and 1997 (1 isolate) and caused damping-off in seedlings (2 isolates) and stem rot and lodging in field tobacco (4 isolates). We confirmed that all binucleate isolates contained only two nuclei per cell. There was variability in the number of nuclei among the multinucleate stem rot (mean 4.2, SE 0.265) and leaf spot (mean 7.5, SE 0.259) isolates. Two tested binucleate Rhizoctonia isolates were pathogenic to 7-week-old tobacco seedlings (cv. Kutsaga 35) in a greenhouse experiment, laid out as a randomized complete block design. Uninoculated healthy plants served as control. Based on a disease rating scale of 1 to 5 (1 = no disease and 5 = >50% stem damage), overall disease incidence was 88.9% 5 days after inoculation with macerated mycelium at the rate of 3.60 × 105 CFU per seedling, applied around the stem base. Over 50% of inoculated seedlings were rated in disease categories 4 and 5. Binucleate Rhizoctonia were consistently isolated from infected plants. A country-wide survey is being conducted to determine the incidence, distribution and severity of diseases caused by binucleate Rhizoctonia on tobacco in Zimbabwe. References: (1) J. S. Cole and Z. Zvenyika. Plant Pathol. 37:271, 1988. (2) S. I. Mpofu and A. M. Julian. J. Phytopathol. 140: 367, 1994.

scholarly journals First Report of Sugar Beet Seedling Damping-Off Caused by Binucleate Rhizoctonia AG-A in China

Plant Disease ◽  
2012 ◽  
Vol 96 (11) ◽  
pp. 1696-1696 ◽  
Author(s):  
P. P. Wang ◽  
X. H. Wu
Keyword(s):  
Sugar Beet ◽  
Disease Incidence ◽  
Soil Surface ◽  
Its Region ◽  
Molecular Characteristics ◽  
Damping Off ◽  
First Report ◽  
Binucleate Rhizoctonia ◽  
Hyphal Diameter ◽  
Wheat Seeds

Sugar beet (Beta vulgaris L.) is grown worldwide and produces one-third of the world's sugar supply. Sugar beet seedling Rhizoctonia damping-off is an important disease mainly caused by Rhizoctonia solani AG-2, AG-4, and AG-5 (2). In 2010, diseased sugar beet seedlings with about 20% incidence affected by damping-off, which showed dark brown lesions on the stems just below the soil surface and portions of the roots, were collected from nurseries in three locations in Heilongjiang province, northeast China. Root fragments taken from the margins of healthy tissues and lesions on roots were surface disinfected with 0.5% sodium hypochlorite for 2 min, rinsed with sterile water, then placed on potato dextrose agar (PDA) and incubated at 25°C in the dark. Three (designed HLJ-RAA1, HLJ-RAB1, HLJ-RAB2) of nine Rhizoctonia isolates were obtained from diseased tissues and preliminarily identified as binucleate Rhizoctonia (BNR) anamorph (teleomorph Ceratobasidium Rogers) species-like. Fungal colonies were white with large amounts of floccose, aerial hyphae. Hyphal cells were determined to be binucleate when stained with 4′-6-diamidino-2-phenylindole (DAPI) (1). No sclerotia were produced after 14 days on PDA. Average hyphal diameter of the three isolates were 4.2, 4.3, and 4.8 μm, respectively. Further, the internal transcribed spacer (ITS) region of rDNA was amplified from the genomic DNA extracted from hyphae by bead beating in 2% CTAB solution using stainless steel beads with primers ITS1 and ITS4. The ITS sequences (GenBank Accession Nos. JX073668, JX073669, and JX073670) were over 99% identical to those of more than 50 Ceratobasidium sp. AG-A isolates (e.g., GenBank Accession No. JQ688054.1; strain HY-15). Therefore, based on morphological and molecular characteristics, these isolates were identified to be BNR AG-A. To determine the pathogenicity of the isolates, sugar beet (cv. HI0305) seedlings were inoculated with wheat seeds colonized with each of the isolated Rhizoctonia strains (one seed per seedling), and grew in pots under greenhouse conditions (3). After 3 weeks, some inoculated plants showed damping-off as observed in the nurseries, whereas noninoculated control plants (sterile wheat seeds only) remained healthy. Disease incidence from the trials averaged 53.3%, 70%, and 53.3% for the isolates HLJ-RAA1, HLJ-RAB1, and HLJ-RAB2, respectively. The three BNR cultures of the pathogens were consistently reisolated from symptomatic roots, and their identities confirmed by morphological and molecular characteristics as described above, fulfilling Koch's postulates. BNR AG-A was previously reported to be pathogenic to soybean, pea, snap bean, and pak choy in China (4). However, to our knowledge, this is the first report of BNR AG-A causing sugar beet seedling damping-off in China. Sugar beet is often grown in crop rotation with soya bean and such a rotation could increase the risk of soilborne infection to either crop by BNR AG-A. References: (1) W. C. Kronland and M. E. Stanghellini. Phytopathology 78:820, 1988. (2) E. O'Sullivan and J. A. Kavanagh. Plant Pathol. 40:128, 1991. (3) C. E. Windels and D. J. Nabben. Phytopathology 79:83, 1989. (4) G. H. Yang et al. J. Phytopathol. 153:333, 2005.

scholarly journals First Report of Damping-Off on Basella rubra Caused by Rhizoctonia solani Anastomosis Group 4 in Florida

Plant Disease ◽  
2012 ◽  
Vol 96 (2) ◽  
pp. 288-288 ◽  
Author(s):  
X. Liao ◽  
Y. Fu ◽  
S. Zhang ◽  
Y. P. Duan
Keyword(s):  
Rhizoctonia Solani ◽  
The United States ◽  
Anastomosis Group ◽  
Pathogenicity Test ◽  
Damping Off ◽  
Ambient Conditions ◽  
Microscopic Appearance ◽  
Stem Base ◽  
First Report ◽  
Intergenic Spacer Region

Indian spinach (Basella rubra L.) is a red stem species of Basella that is cultivated worldwide as an ornamental and the aerial parts are also consumed as a vegetable. In May of 2011, symptoms of damping-off were observed on approximately 10% of the plants at the stem base around the soil line of seedlings in a greenhouse in Homestead, FL. Lesions were initially water soaked, grayish to dark brown, irregular in shape, and sunken in appearance on large plants, causing the infected seedlings to collapse and eventually die. Symptomatic stem tissue was surface sterilized with 0.6% sodium hypochlorite, rinsed in sterile distilled water, air dried, and plated on potato dextrose agar (PDA). Plates were incubated at 25°C in darkness for 3 to 5 days. A fungus was isolated in all six isolations from symptomatic tissues on PDA. Fungal colonies on PDA were light gray to brown with abundant growth of mycelia, and the hyphae tended to branch at right angles when examined under a microscope. A septum was always present in the branch of hyphae near the originating point and a slight constriction at the branch was observed. Neither conidia nor conidiophores were found from the cultures on PDA. The characteristics of hyphae, especially the right angle branching of mycelia, indicate close similarity to those of Rhizoctonia solani (2,3). The internal transcribed spacer (ITS) region of rDNA was amplified with the primers ITS1/ITS4 and sequenced (GenBank Accession No. JN545836). Subsequent database searches by the BLASTN program indicated that the resulting sequence had a 100% identity over 472 bp with the corresponding gene sequence of R. solani anastomosis group (AG) 4 (GenBank Accession No. JF701752.1), a fungal pathogen reported to cause damping-off on many crops. Pathogenicity was confirmed through inoculation of healthy India spinach plants with the hyphae of isolates. Four 4-week-old plants were inoculated with the isolates by placing a 5-mm PDA plug of mycelia at the stem base and covering with a thin layer of the soil. Another four plants treated with sterile PDA served as a control. After inoculation, the plants were covered with plastic bags for 24 h and maintained in a greenhouse with ambient conditions. Four days after inoculation, water-soaked, brown lesions, identical to the symptoms described above, were observed on the stem base of all inoculated plants, whereas no symptoms developed on the control plants. The fungus was isolated from affected stem samples, and the identity was confirmed by microscopic appearance of the hyphae and sequencing the ITS1/ITS4 intergenic spacer region, fulfilling Koch's postulates. This pathogenicity test was conducted twice. R. solani has been reported to cause damping-off of B. rubra in Ghana (1) and Malaysia (4). To our knowledge, this is the first report of damping-off caused by R. solani AG-4 on Indian spinach in Florida and the United States. With the increased interest in producing Asian vegetables for food and ornamental purposes, the occurrence of damping-off on Indian spinach needs to be taken into account when designing programs for disease management in Florida. References: (1) H. A. Dade. XXIX. Bull. Misc. Inform. 6:205, 1940. (2) J. R. Parmeter et al. Phytopathology 57:218, 1967. (3) B. Sneh et al. Identification of Rhizoctonia species. The American Phytopathological Society, St Paul, MN, 1991. (4) T. H. Williams and P. S. W. Liu. Phytopathol. Pap. 19:1, 1976.

Mycelial Interactions and the Potential Use of Tuft Formation in Characterizing Rhizoctonia solani Isolates Infecting Cereals

1993 ◽  
Vol 41 (2) ◽  
pp. 253 ◽  
Author(s):  
HA Yang ◽  
K Sivasithamparam ◽  
PA Obrien
Keyword(s):  
Rhizoctonia Solani ◽  
Anastomosis Group ◽  
Potato Dextrose Agar ◽  
Bare Patch ◽  
Field Isolates ◽  
Mycelial Interactions ◽  
Causal Pathogen ◽  
Patch Disease ◽  
Potential Use ◽  
Compatible Interactions

Field isolates of Rhizoctonia solani anastomosis group (AG) 8, the most important causal pathogen of cereal bare-patch disease, were paired with each other and with tester strains of other AGs on potato-dextrose agar amended with charcoal (PDCA) to investigate mycelial interactions. Pairings among AG 8 field isolates produced compatible interactions of either tuft or merging reactions. Tufts formed between all paired field isolates from different pectic zymogram groups (ZGs) within AG 8, but pairings between genetically identical isolates showed merging reactions. Pairings of AG 8 field isolates with the tester strains of the other AGs led to incompatible interactions varying from merging line to barrage reactions. As formation of a tuft indicates that the paired isolates are able to anastomose and to form viable heterokaryons, the testing of mycelial interaction types, highlighted by tuft formation, may be used as a rapid procedure to characterise field isolates of R. solani obtained from cereals.

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