scholarly journals First Report of Sclerotium rolfsii on Catharanthus roseus

Plant Disease ◽  
2000 ◽  
Vol 84 (2) ◽  
pp. 200-200
Author(s):  
G. E. Holcomb
Keyword(s):  
Catharanthus Roseus ◽  
Fungal Pathogen ◽  
Baton Rouge ◽  
Sclerotium Rolfsii ◽  
The United States ◽  
Madagascar Periwinkle ◽  
Basal Stem Rot ◽  
First Report ◽  
Pathogenicity Tests ◽  
Stem Necrosis

Wilt, blight, and stem necrosis were observed on Catharanthus roseus (L.) G. Don ‘Mediterranean Deep Rose’ (MDR) plants (Madagascar or rose periwinkle) in August 1999 at Burden Research Plantation in Baton Rouge, LA. MDR was the only prostrate-form cultivar and the only cultivar of 11 that was diseased. Twelve of twenty-four plants of cv. MDR were killed in the trial planting. White mycelia and small (1 mm diameter) light brown sclerotia were present at the base of infected plants. The suspect fungus was isolated consistently on acidified water agar and maintained on acidified potato dextrose agar (APDA). Pathogenicity tests were done by pipetting 1 ml of blended inoculum (contents of one 7-day-old plate culture grown on APDA in 100 ml of deionized water) at the base of nine 15-cm-tall Madagascar periwinkle plants. Inoculated and noninoculated plants were held in a dew chamber for 3 days at 28°C and placed in a greenhouse where temperatures ranged between 25 and 31°C. All inoculated plants showed wilt, blight, and basal stem rot after 3 days and were dead after 10 days. Noninoculated plants remained symptomless. The fungal pathogen was identified as Sclerotium rolfsii Sacc. and was reisolated from inoculated plants. The fungus was previously reported on Lochnera rosea (L.) Rchb. (=C. roseus) from Taiwan (1). This is the first report of the occurrence of S. rolfsii on Madagascar periwinkle in the United States. Reference: (1) K. Goto. Trans. Nat. Hist. Soc. Formosa 23:37, 1933.

scholarly journals First Report of Web Blight on Verbena Caused by Rhizoctonia solani

Plant Disease ◽  
2000 ◽  
Vol 84 (4) ◽  
pp. 492-492 ◽  
Author(s):  
G. E. Holcomb ◽  
D. E. Carling
Keyword(s):  
Rhizoctonia Solani ◽  
Fungal Pathogen ◽  
Baton Rouge ◽  
Anastomosis Group ◽  
First Report ◽  
Foliage Blight ◽  
Pathogenicity Tests ◽  
Stem Lesions ◽  
Web Blight ◽  
Branch Death

Web blight was observed on verbena (Verbena × hybrida) during July 1999 in a cultivar trial planting at Burden Research Plantation in Baton Rouge, LA. Foliage blight, stem lesions, and branch death were common symptoms on 12 of 24 cultivars in the trial. Plant death occurred in cvs. Babylon Florena (one of four plants), Purple Princess (two of four plants), and Taylortown Red (two of four plants). Isolations from infected leaves and stems on acidified water agar consistently yielded a fungus with the mycelial and cultural characteristics of Rhizoctonia solani. Pathogenicity tests were carried out by placing 5-day-old fungal mycelial plugs, grown on acidified potato dextrose agar, at the base of healthy verbena stems and holding plants in a dew chamber at 26°C. After 3 days, foliage blight and stem lesions appeared on inoculated plants, and plants were moved to a greenhouse where temperatures ranged from 23 to 32°C. Seven of nine inoculated plants died after 7 days; noninoculated plants remained healthy. The fungal pathogen was reisolated from all inoculated plants. The fungus was identified as R. solani anastomosis group (AG)-1 IB based on multinucleate condition, type of sclerotia produced, and ability to anastomose with R. solani tester isolates of AG-1 IB. This is the first report of web blight on verbena.

scholarly journals First Report of Web Blight Caused by Rhizoctonia solani on Catharanthus roseus in Louisiana

Plant Disease ◽  
2002 ◽  
Vol 86 (11) ◽  
pp. 1272-1272 ◽  
Author(s):  
G. E. Holcomb ◽  
D. E. Carling
Keyword(s):  
Catharanthus Roseus ◽  
First Year ◽  
Culture Dish ◽  
Madagascar Periwinkle ◽  
First Report ◽  
Bedding Plants ◽  
Leaf Spots ◽  
Rainy Weather ◽  
Pathogenicity Tests ◽  
Web Blight

Web (aerial) blight was observed in field plots of Catharanthus roseus (L.) G. Don (Madagascar periwinkle) during three consecutive summers at the Burden Research Center in Baton Rouge. Leaf spots formed first, followed by a general blighting of leaves and stems that resulted in circular areas of dead plants in the plots. Dead leaves were matted together but remained attached to plants. Mycelia, and occasionally small, brown sclerotia (1 to 3 mm) were observed on blighted foliage. During the first year, only prostrate-growing cultivars belonging to the Mediterranean series of C. roseus were infected, but in 2001 and 2002 upright-growing cultivars as well as those with prostrate growth habit became infected. The disease occurred in July and August during periods of hot, humid, and rainy weather. Among 52 cultivars in the 2001 trial, only ‘Tropicana Pink’, ‘Tropicana Rose’ and ‘Stardust Orchid’ were disease free. A Rhizoctonia sp. was consistently isolated from diseased plants and further characterized as R. solani Kühn AG-1 based on its multinucleate cells and hyphal anastomosis with several AG-1 tester isolates. On potato dextrose agar, colonies displayed morphologies with characteristics of AG-1 IA and AG-1 IB, therefore, identification to AG subgroup was not made. Mature colonies ranged from light tan to brown and produced sclerotia, individually or in clumps, at the edge of the culture dish. Pathogenicity tests were performed by placing agar blocks, taken from the margins of 7-day-old cultures, on stems of eight healthy Madagascar periwinkle plants (15 to 20 cm tall). Inoculated and noninoculated control plants were held in a dew chamber at 26°C for 3 days and then moved to a greenhouse. Leaves on all inoculated plants developed water-soaked spots that turned dark brown or black prior to death, whereas noninoculated plants remained healthy. R. solani was reisolated from inoculated plants and its cultural characteristics were similar to those of the original isolate. Web blight occurs in Louisiana on Madagascar periwinkle used as landscape bedding plants, but has not been observed on container-grown plants. Web blight caused by R. solani AG-1 was previously reported on Madagascar periwinkle from Alabama (1). R. solani AG-1 has been reported previously as causing web blight in Louisiana on rosemary (2), dianthus (4), and verbena (3). To our knowledge, this is the first report of web blight on Madagascar periwinkle (C. roseus) in Louisiana. References: (1) A. K. Hagan and J. M. Mullen. Plant Dis. 77:1169, 1993. (2) G. E. Holcomb. Plant Dis. 76:859, 1992. (3) G. E. Holcomb and D. E. Carling. Plant Dis. 84:492, 2000. (4) G. E. Holcomb and D. E. Carling. Plant Dis. 84:1344, 2000.

scholarly journals First Report of Sclerotium rolfsii on Jerusalem Cherry (Solanum pseudocapsicum) in Europe

Plant Disease ◽  
2000 ◽  
Vol 84 (9) ◽  
pp. 1048-1048
Author(s):  
A. Garibaldi ◽  
A. Minuto ◽  
M. L. Gullino
Keyword(s):  
United States ◽  
Sclerotium Rolfsii ◽  
Soil Surface ◽  
The United States ◽  
Northern Italy ◽  
Ornamental Plant ◽  
Potato Dextrose Agar ◽  
First Report ◽  
Initial Symptoms ◽  
Stem Necrosis

Jerusalem cherry (Solanum pseudocapsicum) has recently become popular as a potted ornamental plant in Italy. During the summer of 1999, a sudden wilt of 60-day-old plants was observed in the Albenga region (Northern Italy), an area of intensive floriculture. Initial symptoms included stem necrosis at the soil line and yellowing and tan discoloration of leaves. As stem necrosis progressed, infected plants wilted and died. Necrotic tissues were covered with whitish mycelium that differentiated into reddish brown, spherical (1 to 2 mm diameter) sclerotia. Sclerotium rolfsii was consistently recovered from the surface of symptomatic stem sections that were disinfected for 1 min in 1% NaOCl and then plated on potato-dextrose agar (PDA) amended with 100 ppm streptomycin sulfate. Pathogenicity of three S. rolfsii isolates was confirmed by inoculating 90-day-old S. pseudocapsicum plants grown in pots. Inoculum consisted of mycelium and sclerotia of the pathogen placed on the soil surface around the base of each plant. Noninoculated plants served as controls. All plants were kept in a growth chamber at 18 to 28°C and RH > 85%. Inoculated plants developed symptoms within 7 days, while control plants remained symptomless. Sclerotia developed on infected tissues and S. rolfsii was reisolated from symptomatic tissues. The disease has been observed in the United States (1), but this is the first report of stem blight of S. pseudocapsicum caused by S. rolfsii in Europe. Reference: (1) S. A. Alfieri, Jr., K. R. Langdon, C. Wehlburg, and J. W. Kimbrough, J. W. Index Plant Dis. Florida Bull. 11:215, 1984.

scholarly journals First Report of Plumeria spp. Rust Caused by Coleosporium plumeriae in Louisiana and Malaysia and Catheranthus roseus, a New Host of this Rust

Plant Disease ◽  
2010 ◽  
Vol 94 (2) ◽  
pp. 272-272 ◽  
Author(s):  
G. E. Holcomb ◽  
M. C. Aime
Keyword(s):  
United States ◽  
Baton Rouge ◽  
Pacific Islands ◽  
The United States ◽  
Plant Diseases ◽  
Nerium Oleander ◽  
Urban Landscapes ◽  
Rust Disease ◽  
Madagascar Periwinkle ◽  
First Report

Plumeria spp., native to tropical America, are popular small trees grown widely in tropical areas of the world and as potted plants elsewhere. P. rubra and P. obtusa cultivars and hybrids are most common. A rust disease of a Plumeria sp. (likely P. rubra based on pointed leaf tips, leaves more than 18 cm (7 inches) long, and high rust susceptibility) was observed in November 2008 and again in June 2009 on homeowner plants in Baton Rouge, LA. A survey of five Baton Rouge retail nurseries in September 2009 revealed that 87% (90 of 103) of the plumeria plants were heavily infected with rust. Early symptoms included numerous 1-mm chlorotic spots on adaxial leaf surfaces followed by leaf chlorosis, necrosis, and abscission. Uredinia were numerous, mostly hypophyllous and yellowish orange. Urediniospores were catenulate, orange en masse, verrucose, globose, ovoid, ellipsoidal or angular, and measured 21.8 to 41.9 × 16.4 to 32.8 μm (average 29.4 × 22.6 μm). The rust was identified as Coleosporium plumeriae Pat. (= C. plumierae) (3). Teliospores were not found during this study. Pathogenicity tests were performed by spraying urediniospores (20,000/ml of deionized water) on three healthy Thai hybrid plumeria plants. Five leaves of each plant were misted with water and covered with plastic bags and three to five leaves were inoculated. Plants were held at 27°C for 27 h in a dew chamber and then moved outdoors. Typical rust symptoms and uredinia with urediniospores developed in 10 days on all inoculated leaves while noninoculated leaves remained healthy. Characteristics and spore measurements matched those of the rust from original infected plants. Additional plumeria rust inoculations were made to other Apocynaceae family members that included Allamanda cathartica, Catheranthus roseus (Madagascar periwinkle), Mandevilla splendens, Nerium oleander, and Vinca major. Catheranthus roseus was very susceptible to C. plumeriae with chlorotic leaf spots developing on the six inoculated plants after 8 days and uredinia with urediniospores appearing after 11 days. None of the other plant genera were susceptible to the rust. Plumeria rust was also observed on plumeria trees in urban landscapes in peninsular (Penang) and Bornean (Kota Kinabalu, Sabah) Malaysia in December 2007. To confirm identity, ~1,000 bp of nuclear rDNA 28S subunit from each (Lousiana, Penang, and Kota Kinabalu) was sequenced with rust-specific primers (1) and shared 100% identity (GenBank No. GU145555-6). Plumeria rust was first found on the island of Guadeloupe (3) and then spread to Central and South America. It has been known from Florida since 1960 under the synonym C. domingense (2), but has not been reported elsewhere in the continental United States. In more recent years, plumeria rust has spread to Hawaii, many Pacific islands, India, China, Taiwan, Thailand, Australia, and Nigeria (4). To our knowledge, this is the first report of plumeria rust from Louisiana and Malaysia and of susceptibility of another member of the Apocynaceae, Madagascar periwinkle, to C. plumeriae. Voucher material from Louisiana and Malaysia has been deposited in the Mycology Herbarium of Louisiana State University (LSUM). References: (1) M. C. Aime. Mycoscience 47:112, 2006. (2) Anonymous. Index of Plant Diseases in the United States. U.S. Dept. Agric. Handb. No. 165. Washington, D.C., 1960. (3) N. Patouillard. Bull. Soc. Mycol. Fr. 18:171, 1902. (4) C. To-Anun et al. Nat. Hist. J. Chulalongkorn Univ. 4:41, 2004.

scholarly journals First Report of Southern Blight of Ruellia brittoniana Caused by Sclerotium rolfsii in Louisiana

Plant Disease ◽  
2004 ◽  
Vol 88 (7) ◽  
pp. 770-770
Author(s):  
G. E. Holcomb
Keyword(s):  
Root Rot ◽  
High Speed ◽  
Sclerotium Rolfsii ◽  
Stem Rot ◽  
Basal Stem Rot ◽  
First Report ◽  
Southern Blight ◽  
Agar Plug ◽  
Leaf Yellowing ◽  
Pathogenicity Tests

Ruellia brittoniana, Mexican petunia, is an herbaceous flowering perennial grown in hardiness zones 8 to 10 in the southern and western United States. Popular dwarf forms with flower colors of white, pink, and blue are used as ground covers and borders. In April of 2003, root and stem rot that caused plant death was observed on cv. Katie (dwarf form, pink flowers) at a wholesale nursery in southern Louisiana. Plants were growing in a vermiculite and sand mix. The grower had purchased the plants from an out-of-state source, and approximately one-half of 1,440 plants were dead or dying. Symptoms included wilt, basal stem rot, and root rot. Peripheral roots were covered with a white mycelial layer that contained white sclerotial initials and small, brown sclerotia. Fungal isolates from infected roots grown on potato dextrose agar (PDA) produced white mycelia and 1- to 2-mm-diameter dark brown sclerotia. Sclerotia were nearly round with smooth surfaces and distributed over the entire colony. Isolates were identified as Sclerotium rolfsii on the basis of mycelial characteristics and color, size, and distribution of sclerotia. Two-month-old seedlings (6 to 10 cm high) of R. brittoniana, from seed of cv. Katie, were used in pathogenicity tests. Inoculum was grown in 10-cm-diameter plastic, culture dishes on PDA medium. Blended inoculum was prepared from a single 1-week-old culture that was composed of mycelia and sclerotia and blended 4 to 6 s at high speed in 100 ml of distilled water. In test one, 5 ml of inoculum was placed at the base of each inoculated plant. In test two, a single 5-mm-diameter agar plug with mycelium plus four sclerotia was placed beside plant stems near soil line. In test three, 5 ml of blended inoculum was dripped on exposed roots after plants were removed from pots. In test four, exposed plant roots were dipped in the blended inoculum. Each test contained 10 inoculated plants, and 10 noninoculated plants served as controls. All plants were placed in a dew chamber maintained at 28°C for 2 days and then returned to a greenhouse to observe development of symptoms and signs of disease. In tests one and two, basal stem rot and wilt developed on inoculated plants after 2 days and after 5 to 8 days all were dead. Inoculated plants from tests three and four were alive 4 months after inoculation, but were showing symptoms including leaf yellowing and drop, moderate to severe root rot, and some plants had begun to show white mycelia and white sclerotial initials on peripheral roots by January 2004. All noninoculated plants remained healthy and S. rolfsii was reisolated from infected plants in each test. To my knowledge, this is the first report of S. rolfsii causing disease on R. brittoniana.

scholarly journals First Report of Leaf Blight Caused by Rhizoctonia solani AG 1B on Madagascar Periwinkle (Catharanthus roseus) in Italy

Plant Disease ◽  
2006 ◽  
Vol 90 (10) ◽  
pp. 1361-1361 ◽  
Author(s):  
A. Garibaldi ◽  
D. Bertetti ◽  
M. L. Gullino
Keyword(s):  
Rhizoctonia Solani ◽  
Catharanthus Roseus ◽  
The United States ◽  
Morphological Characters ◽  
Leaf Blight ◽  
Pathogenicity Test ◽  
Madagascar Periwinkle ◽  
Public Park ◽  
First Report ◽  
Leaf Petiole

Madagascar periwinkle (Catharanthus roseus), a plant belonging to the Apocynaceae family, is used for parks and gardens and sometimes grown in pots. At the end of the summer of 2005, a leaf blight was observed on plants in a public park of Torino. Semicircular, water-soaked lesions developed on leaves just above the soil line at the leaf-petiole junction and later along the leaf margins. Lesions expanded for several days along the midvein until the entire leaf was destroyed. Blighted leaves turned brown, withered, clung to the shoots, and matted on the surrounding foliage. Although lesions were not seen on the stem, affected plants often died leaving wide empty areas. Mycelia of the pathogen were often seen on and suspended between the leaves. Blight progressed from the leaves to the shoot tip. The diseased tissue was disinfected for 1 min in 1% NaOCl and plated on potato dextrose agar (PDA) amended with 100 μg/l streptomycin sulphate. A fungus with the morphological characters of Rhizoctonia solani was consistently and readily isolated and maintained in pure culture after single-hyphal tipping (4). The isolates of R. solani obtained from affected plants were successfully anastomosed with tester isolate AG 1 (ATCC 58946). 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 are consistent with other reports on anastomosis reactions (2). Pairing was also made with AG 2, 3, 4, 5, 7, and 11, with no anastomoses observed between the isolates and testers. Sclerotia were subspheroid in shape and had a size of 1 mm, which indicated that this pathogen was in subgroup 1B (4). For pathogenicity tests, the inoculum of R. solani was prepared by growing the pathogen on PDA for 7 days. Plants of C. roseus were grown in 3-liter containers (2 plants per pot) on a steam disinfested substrate (peat/ pomix/pine bark/clay). Artificial inoculation was carried out on 7-day-old plants by placing numerous fragments of PDA cultures on the leaves of the plants. Plants inoculated with PDA alone served as control treatments. Three replicates were used. Plants were maintained in a glasshouse at 20 to 25°C. The first symptoms, similar to those observed in the public park, developed 5 days after inoculation, and R. solani was consistently reisolated from infected plants. Control plants remained healthy. The pathogenicity test was carried out twice with similar results. This is, to our knowledge, the first report of R. solani on periwinkle in Italy. The same disease was reported in India (1) and the United States (3). References: (1) R. Balasubramanian and K. S. Bhama. Indian Phytopathol. 30:556, 1977. (2) D. E. Carling. Grouping in Rhizoctonia solani by hyphal anastomosis reactions. Pages 37–47 in: Rhizoctonia Species: Taxonomy, Molecular Biology, Ecology, Pathology and Disease Control. B. Sneh et al., eds. Kluwer Academic Publishers, the Netherlands, 1996. (3) A. K. Hagan and J. M. Mullen Plant Dis. 77:1169, 1993. (4) B. Sneh et al. Identification of Rhizoctonia Species. The American Phytopathological Society, St Paul, MN, 1991.

scholarly journals First Report of Southern Blight Caused by Sclerotium rolfsii on St.-John's-Wort

Plant Disease ◽  
1999 ◽  
Vol 83 (7) ◽  
pp. 696-696 ◽  
Author(s):  
A. P. Keinath ◽  
J. W. Rushing ◽  
R. J. Dufault
Keyword(s):  
Sclerotium Rolfsii ◽  
Soil Surface ◽  
The United States ◽  
Pathogenicity Test ◽  
First Report ◽  
Southern Blight ◽  
St John’S Wort ◽  
St John's Wort ◽  
Pathogenicity Tests ◽  
Hypericum Perforatum L

Interest in commercial production of common St.-John's-wort (Hypericum perforatum L.), an herb that is dried, processed, and used as an anti-depressant medication, is increasing. In August 1998, St.-John's-wort growing in the field at Charleston, SC, showed blight symptoms. Leaves on prostrate branches turned reddish-yellow, then brown, and then abscised. As the disease progressed, branches and approximately 10% of the plants were killed. Coarse, white mycelia were present on the bases of dead branches. Segments cut from symptomatic branches were disinfested in 0.5% sodium hypochlorite and placed on potato dextrose agar (PDA) at 25°C. Sclerotium rolfsii Sacc. was isolated from one of 12 branches with discolored leaves and six of six dead branches. For pathogenicity tests, sclerotia were harvested from 6-week-old cultures on PDA. Ten-week-old St.-John's-wort plants, growing in potting mix in 10-cm pots, were inoculated by placing four sclerotia on the soil surface 1 to 1.5 cm from the main stem of each plant. Plants were grown in a greenhouse at 90% relative humidity and 25 to 35°C. Single blighted branches were observed on three plants 12 days after inoculation and all plants were blighted 28 days after inoculation. S. rolfsii was recovered from 10 and 9 of 10 plants inoculated with isolates of S. rolfsii from St.-John's-wort and tomato, respectively. All 10 noninoculated plants remained symptomless. The pathogenicity test was repeated and the results were similar. This is the first report of S. rolfsii causing Southern blight on St.-John's-wort in the United States.

scholarly journals First Report of Sclerotinia sclerotiorum on Campanula carpatica and Schizanthus × wisetonensis in Italy

Plant Disease ◽  
2002 ◽  
Vol 86 (1) ◽  
pp. 71-71
Author(s):  
A. Garibaldi ◽  
A. Minuto ◽  
M. L. Gullino
Keyword(s):  
United States ◽  
Sclerotinia Sclerotiorum ◽  
Ornamental Plants ◽  
Soil Surface ◽  
The United States ◽  
First Report ◽  
Potted Plants ◽  
Initial Symptoms ◽  
Stem Necrosis ◽  
Campanula Carpatica

The production of potted ornamental plants is very important in the Albenga Region of northern Italy, where plants are grown for export to central and northern Europe. During fall 2000 and spring 2001, sudden wilt of tussock bellflower (Campanula carpatica Jacq.) and butterfly flower (Schizanthus × wisetonensis Hort.) was observed on potted plants in a commercial greenhouse. Initial symptoms included stem necrosis at the soil line and yellowing and tan discoloration of the lower leaves. As stem necrosis progressed, infected plants growing in a peat, bark compost, and clay mixture (70-20-10) wilted and died. Necrotic tissues were covered with whitish mycelia that produced dark, spherical (2 to 6 mm diameter) sclerotia. Sclerotinia sclerotiorum was consistently recovered from symptomatic stem pieces of both plants disinfested for 1 min in 1% NaOCl and plated on potato dextrose agar amended with streptomycin sulphate at 100 ppm. Pathogenicity of three isolates obtained from each crop was confirmed by inoculating 45- to 60-day-old C. carpatica and Schizanthus × wisetonensis plants grown in containers (14 cm diameter). Inoculum that consisted of wheat kernels infested with mycelia and sclerotia of each isolate was placed on the soil surface around the base of previously artificially wounded or nonwounded plants. Noninoculated plants served as controls. All plants were maintained outdoors where temperatures ranged between 8 and 15°C. Inoculated plants developed symptoms of leaf yellowing, followed by wilt, within 7 to 10 days, while control plants remained symptomless. White mycelia and sclerotia developed on infected tissues and S. sclerotiorum was reisolated from inoculated plants. To our knowledge, this is the first report of stem blight of C. carpatica and Schizanthus × wisetonensis caused by S. sclerotiorum in Italy. The disease was previously observed on C. carpatica in Great Britain (2) and on Schizanthus sp. in the United States (1). References: (1) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989. (2) J. Rees. Welsh J. Agric. 1:188, 1925.

scholarly journals First Report of Phomopsis citri Associated with Dieback of Citrus lemon in India

Plant Disease ◽  
2014 ◽  
Vol 98 (9) ◽  
pp. 1281-1281 ◽  
Author(s):  
S. Mahadevakumar ◽  
Vandana Yadav ◽  
G. S. Tejaswini ◽  
S. N. Sandeep ◽  
G. R. Janardhana
Keyword(s):  
Fungal Pathogen ◽  
The United States ◽  
Apical Region ◽  
Post Inoculation ◽  
Pathogenicity Test ◽  
Conidial Suspension ◽  
Internal Transcribed Spacer Region ◽  
Productivity Level ◽  
First Report ◽  
Dieback Disease

Lemon (Citrus lemon (L.) Burm. f.) is an important fruit crop cultivated worldwide, and is grown practically in every state in India (3). During a survey conducted in 2013, a few small trees in a lemon orchard near Mysore city (Karnataka) (12°19.629′ N, 76°31.892′ E) were found affected by dieback disease. Approximately 10 to 20% of trees were affected as young shoots and branches showed progressive death from the apical region downward. Different samples were collected and diagnosed via morphological methods. The fungus was consistently isolated from the infected branches when they were surface sanitized with 1.5% NaOCl and plated on potato dextrose agar (PDA). Plates were incubated at 26 ± 2°C for 7 days at 12/12 h alternating light and dark period. Fungal colonies were whitish with pale brown stripes having an uneven margin and pycnidia were fully embedded in the culture plate. No sexual state was observed. Pycnidia were globose, dark, 158 to 320 μm in diameter, and scattered throughout the mycelial growth. Both alpha and beta conidia were present within pycnidia. Alpha conidia were single celled (5.3 to 8.7 × 2.28 to 3.96 μm) (n = 50), bigittulate, hyaline, with one end blunt and other truncated. Beta conidia (24.8 to 29.49 × 0.9 to 1.4 μm) (n = 50) were single celled, filiform, with one end rounded and the other acute and curved. Based on the morphological and cultural features, the fungal pathogen was identified as Phomopsis citri H.S. Fawc. Pathogenicity test was conducted on nine healthy 2-year-old lemon plants via foliar application of a conidial suspension (3 × 106); plants were covered with polythene bags for 6 days and maintained in the greenhouse. Sterile distilled water inoculated plants (in triplicate) served as controls and were symptomless. Development of dieback symptoms was observed after 25 days post inoculation and the fungal pathogen was re-isolated from the inoculated lemon trees. The internal transcribed spacer region (ITS) of the isolated fungal genomic DNA was amplified using universal-primer pair ITS1/ITS4 and sequenced to confirm the species-level diagnosis (4). The sequence data of the 558-bp amplicon was deposited in GenBank (Accession No. KJ477016.1) and nBLAST search showed 99% homology with Diaporthe citri (teleomorph) strain 199.39 (KC343051.1). P. citri is known for its association with melanose disease of citrus in India, the United States, and abroad. P. citri also causes stem end rot of citrus, which leads to yield loss and reduction in fruit quality (1,2). Dieback disease is of serious concern for lemon growers as it affects the overall productivity level of the tree. To the best of our knowledge, this is the first report of P. citri causing dieback of lemon in India. References: (1) I. H. Fischer et al. Sci. Agric. (Piracicaba). 66:210, 2009. (2) S. N. Mondal et al. Plant Dis. 91:387, 2007. (3) S. P. Raychaudhuri. Proc. Int. Soc. Citriculture 1:461, 1981. (4) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA, 1990.

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