scholarly journals Xanthomonas Blight of Onion in South Africa

Plant Disease ◽  
2001 ◽  
Vol 85 (4) ◽  
pp. 442-442 ◽  
Author(s):  
J. J. Serfontein
Keyword(s):  
South Africa ◽  
Tween 80 ◽  
Pathogenicity Test ◽  
Foliar Blight ◽  
Foliar Symptoms ◽  
Plastic Bags ◽  
Overhead Irrigation ◽  
Allium Cepa L ◽  
Pure Cultures ◽  
Biolog Gn

During April 1999, a foliar blight of onion (Allium cepa L. ‘Granex 33’) was reported in an early commercial planting under center pivot irrigation in the Limpopo Valley of the Northern Province of South Africa. Regular fungicide sprays failed to inhibit the progress of the disease. Foliar symptoms started as water-soaked lesions that elongated and turned chlorotic followed by tissue collapse in some leaves. Leaves often collapsed at the point of infection. Bulb size was severely reduced and premature leaf death caused irregular maturation and bulb size in the field. The symptoms were similar to those of Xanthomonas blight, described on the same cultivar in Hawaii (1). Microscopic examination of hand cut sections trough lesion margins showed bacterial streaming. Isolation on semi-selective diagnostic milk Tween agar (2) yielded almost pure cultures of a typical xanthomonad. The mucoid, yellow pigmented bacterium was rod shaped, gram negative, catalase positive, oxidase negative, utilized glucose oxidatively, and was lypolytic (Tween 80), proteolytic (skimmed milk), and amolytic. Biolog GN Microplate profiles as read by the MicroLog database release 3.50 (Biolog, Hayward, CA) were similar to those of a pathovar (similarity indices of 0.29 to 0.71). Symptoms were successfully reproduced on glasshouse grown Granex 33 seedlings at the five-leaf stage by spray and syringe inoculations (1) and the pathogen reisolated as described above. Ten seedlings were used in the pathogenicity test, of which five served as controls. After inoculation, seedlings were covered overnight with plastic bags, after which bags were removed and seedlings grown in the greenhouse at 24 to 30°C and natural light until symptom development. Attempts to isolate the pathogen from the seed lot used to plant the affected field were unsuccessful. The disease re-occurred in early plantings of Granex 33 on the same farm in April 2000 toward the end of an unusually wet summer rainy season. Damage caused by the disease was so severe in one early planting that it was plowed under. High temperatures and humid conditions combined with overhead irrigation could have enhanced disease development and spread during the early growth of the crop. No further spread was observed during cooler and drier weather later in the season. References: (1) A. M. Alvarez et al. Phytopathology 68:1132, 1978. (2) T. Goszczynska and J. J. Serfontein. J. Microbiol. Methods 32:65, 1998.

scholarly journals First Report of a Leaf Blight and Bulb Decay of Onion by Pantoea ananitas in Colorado

Plant Disease ◽  
2000 ◽  
Vol 84 (7) ◽  
pp. 808-808 ◽  
Author(s):  
H. F. Schwartz ◽  
K. Otto
Keyword(s):  
Acid Methyl Ester ◽  
Heavy Rain ◽  
Storm Damage ◽  
First Report ◽  
Foliar Blight ◽  
Visual Evidence ◽  
Plastic Bags ◽  
Allium Cepa L ◽  
Scattered Fields ◽  
Physiological Tests

Sweet Spanish onion (Allium cepa L.) cultivars grown in southern Colorado displayed symptoms of foliar blight and bulb rotting after bulb initiation in early July of 1997, 1998, and 1999. This disease appears identical to that reported from infected onions in Georgia in 1997 (1). Leaf blighting began as whitish to tan lesions, which rapidly coalesced, causing a general wilt, discoloration, and death of affected foliage. A yellow-cream to light orange discoloration progressed into bulbs, resulting in the rotting of neck tissue and between scales. Infection of more than 70% of onion plants exposed to heavy rain and storm damage after bulb initiation occurred in scattered fields in Otero County. Gram negative, rod-shaped, yellow-colored bacteria were consistently recovered from infected foliar and bulb tissues on nutrient agar during this 3-year period. Physiological tests showed that the bacteria utilized glucose in an oxidative and fermentative manner and were catalase positive and oxidase negative. Two strains recovered during 1997 were identified by Microbe Inotech Laboratories (St. Louis, MO) as Pantoea ananas by gas-chromatography fatty acid methyl ester analysis, with similarity indices of 0.70 and 0.79. A literature search determined that the accepted classification is now Pantoea ananatis Serrano (2). To confirm pathogenicity, a 0.5- to 1.0-ml suspension of bacteria (108 CFU/ml sdw) of one of the strains was injected into firm onion bulbs (7.5 to 10.0 cm diameter). After incubation for 14 days at 22°C in enclosed plastic bags in the dark, bulbs were cut in half and scored for visual evidence of yellow to tan discoloration and initial dry rotting prior to reisolation of the pathogen from five of eight inoculated bulbs. No discoloration or disease developed on eight control bulbs injected with water. To our knowledge, this is the first report of P. ananatis from onion grown in Colorado and the western United States. References: (1) R. D. Gitaitis and J. D. Gay. Plant Dis. 81:1096, 1997. (2) H. G. Truper and L. de Clari. Int. J. System. Bacteriol. 47:908, 1997.

scholarly journals First Report of Leaf Spot and Root Rot Caused by Phoma betae on Beta vulgaris subsp. vulgaris (Garden Beet Group) in Italy

Plant Disease ◽  
2007 ◽  
Vol 91 (11) ◽  
pp. 1515-1515 ◽  
Author(s):  
A. Garibaldi ◽  
G. Gilardi ◽  
D. Bertetti ◽  
M. L. Gullino
Keyword(s):  
Beta Vulgaris ◽  
Morphological Characteristics ◽  
Its Region ◽  
Pathogenicity Test ◽  
Vegetable Crops ◽  
Plastic Bags ◽  
Blastn Analysis ◽  
Commercial Farms ◽  
Pathogenicity Tests ◽  
Phoma Betae

In the winter of 2007 in Piedmont (northern Italy), symptoms of a previously unknown disease were observed on beet (Beta vulgaris L. subsp. vulgaris) (garden beet group) grown under a tunnel on several commercial farms near Cuneo. First symptoms appeared on 1-month-old plants, occurring as brown, round-to-oval spots as much as 2 cm in diameter with dark concentric rings near the perimeter. Small, dark pycnidia were present throughout the spots in concentric rings. Generally, older, lower leaves were affected more than the younger ones. Ten to fifteen percent of the plants were affected. Symptoms on the roots began near the crown as small, dark, sunken spots that became soft and water soaked. Eventually, spots on the roots turned dark brown to black and black lines separated diseased and healthy tissues. Older infected tissues were black, dry, shrunken, and spongy. Pycnidia were not observed on affected roots. From infected leaves and roots, a fungus was consistently isolated on potato dextrose agar (PDA) amended with 25 mg/l of streptomycin. The fungus was grown on PDA and maintained at 22°C (12 h of light, 12 h of dark). After 10 days, black pycnidia (130 to 328 [204] μm in diameter) developed, releasing abundant hyaline, elliptical, nonseptate conidia measuring 3.9 to 6.7 (5.1) × 2.4 to 5.9 (3.6) μm. On the basis of its morphological characteristics, the fungus was identified as a Phoma sp. (1). The internal transcribed spacer (ITS) region was amplified using primers ITS4/ITS6 (2) and sequenced. BLASTn analysis of the 557 bp obtained showed an E-value of 0.0 with Phoma betae. The nucleotide sequence has been assigned GenBank Accession No. EU003450. Pathogenicity tests were performed by spraying leaves of healthy 20-day-old potted B. vulgaris plants with a spore and mycelial suspension (1 × 106 spores or mycelial fragments per ml). Noninoculated plants sprayed only with water served as controls. Fifteen plants (three per pot) were used for each treatment. Plants were covered with plastic bags for 5 days after inoculation and kept in a growth chamber at 20°C. Symptoms previously described developed on leaves of all inoculated plants 5 days after inoculation, while control plants remained healthy. Later, pycnidia and conidia, with the same dimensions and characteristics previously described, were observed on the infected leaves. The fungus was consistently reisolated from the lesions of the inoculated plants. The pathogenicity test was carried out twice. P. betae on B. vulgaris var. cycla has been reported in Canada (3) as well as in other countries. The same pathogen was reported in Italy on sugar beet (2). References: (1) G. H. Boerema and G. J. Bollen. Persoonia 8:111, 1975. (2) A. Canova. Inf. Fitopatol. 16:207, 1966. (3) D. E L. Cooke and J. M. Duncan. Mycol. Res. 101:667, 1997. (4) J. R. Howard et al. Diseases of Vegetable Crops in Canada. Canadian Phytopathological Society, 1994.

scholarly journals First Report of Phytophthora drechsleri Associated with Stem and Foliar Blight of Gynura bicolor in Taiwan

Plant Disease ◽  
2011 ◽  
Vol 95 (7) ◽  
pp. 874-874 ◽  
Author(s):  
Y. M. Shen ◽  
C. H. Chao ◽  
H. L. Liu
Keyword(s):  
Disease Incidence ◽  
Morphological Characteristics ◽  
Hyphal Growth ◽  
Pathogenicity Test ◽  
Distilled Water ◽  
First Report ◽  
Foliar Blight ◽  
Dual Cultures ◽  
Phytophthora Drechsleri ◽  
Gynura Bicolor

Gynura bicolor (Roxb. ex Willd.) DC., known as Okinawa spinach or hong-feng-cai, is a commonly consumed vegetable in Asian countries. In May 2010, plants with blight and wilt symptoms were observed in commercial vegetable farms in Changhua, Taiwan. Light brown-to-black blight lesions developed from the top of the stems to the petioles and extended to the base of the leaves. Severely infected plants declined and eventually died. Disease incidence was approximately 20%. Samples of symptomatic tissues were surface sterilized in 0.6% NaOCl and plated on water agar. A Phytophthora sp. was consistently isolated and further plated on 10% unclarified V8 juice agar, with daily radial growths of 7.6, 8.6, 5.7, and 2.4 mm at 25, 30, 35, and 37°C, respectively. Four replicates were measured for each temperature. No hyphal growth was observed at 39°C. Intercalary hyphal swellings and proliferating sporangia were produced in culture plates flooded with sterile distilled water. Sporangia were nonpapillate, obpyriform to ellipsoid, base tapered or rounded, and 43.3 (27.5 to 59.3) × 27.6 (18.5 to 36.3) μm. Clamydospores and oospores were not observed. Oospores were present in dual cultures with an isolate of P. nicotianae (p731) (1) A2 mating type, indicating that the isolate was heterothallic. A portion of the internal transcribed spacer sequence was deposited in GenBank (Accession No. HQ717146). The sequence was 99% identical to that of P. drechsleri SCRP232 (ATCC46724) (3), a type isolate of the species. The pathogen was identified as P. drechsleri Tucker based on temperature growth, morphological characteristics, and ITS sequence homology (3). To evaluate pathogenicity, the isolated P. drechsleri was inoculated on greenhouse-potted G. bicolor plants. Inoculum was obtained by grinding two dishes of the pathogen cultured on potato dextrose agar (PDA) with sterile distilled water in a blender. After filtering through a gauze layer, the filtrate was aliquoted to 240 ml. The inoculum (approximately 180 sporangia/ml) was sprayed on 24 plants of G. bicolor. An equal number of plants treated with sterile PDA processed in the same way served as controls. After 1 week, incubation at an average temperature of 29°C, blight and wilt symptoms similar to those observed in the fields appeared on 12 inoculated plants. The pathogen was reisolated from the lesions of diseased stems and leaves, fulfilling Koch's postulates. The controls remained symptomless. The pathogenicity test was repeated once with similar results. G. bicolor in Taiwan has been recorded to be infected by P. cryptogea (1,2), a species that resembles P. drechsleri. The recorded isolates of P. cryptogea did not have a maximal growth temperature at or above 35°C (1,2), a distinctive characteristic to discriminate between the two species (3). To our knowledge, this is the first report of P. drechsleri being associated with stem and foliar blight of G. bicolor. References: (1) P. J. Ann. Plant Pathol. Bull. 5:146, 1996. (2) H. H. Ho et al. The Genus Phytophthora in Taiwan. Institute of Botany, Academia Sinica, Taipei, 1995. (3) R. Mostowfizadeh-Ghalamfarsa et al. Fungal Biol. 114:325, 2010.

Xylophilus ampelinus. [Descriptions of Fungi and Bacteria].

1991 ◽  
Author(s):  
J. F. Bradbury
Keyword(s):  
South Africa ◽  
Geographical Distribution ◽  
Bacterial Blight ◽  
Early Spring ◽  
Distribution Map ◽  
Stunted Growth ◽  
Leaf Spots ◽  
Overhead Irrigation ◽  
Sources Of Infection ◽  
Xylophilus Ampelinus

Abstract A description is provided for Xylophilus ampelinus. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOST: Vitis vinifera. DISEASE: Bacterial blight of the grapevine; 'Tsilik marasi' in Greece; 'Maladie d'Oleron' in France; 'Mel nero' in Italy; 'Vlamsiekte' in South Africa. In early spring buds on infected spurs fail to open or make stunted growth which eventually dies. Affected spurs often appear slightly swollen because of hyperplasia of the cambial tissue. Cracks appear along such spurs and enlarge to form cankers. Young shoots may develop pale yellowish-green spots on the lowest internodes. These expand upwards on the shoot, darken, crack and develop into cankers. Cracks and later cankers also form on more woody branches later in spring. In summer, cankers are often seen on the sides of petioles causing a characteristic one-sided necrosis of the leaf. They may also appear on main and secondary flower and fruit stalks. Leaf spots and marginal necrosis sometimes occur. Gum formation is not necessarily a symptom. GEOGRAPHICAL DISTRIBUTION: South Africa, France, Greece (including Crete), Italy (including Sardinia and Sicily), Spain, Turkey (68, 367). (IMI Distribution Map 531, ed 2, 1986). TRANSMISSION: Bacteria are carried by moisture to wounds, leaf scars and other sites where infection may take place. Primary infection can take place without wounding. Grafting and pruning can cause much spread of the disease. Overhead irrigation contributes to spread and development (51, 551). Observations indicate that sources of infection survive in vines even after removal of visibly infected parts.

scholarly journals First Report of Colletotrichum siamense Causing Anthracnose of Monstera deliciosa in Zhanjiang, China

Plant Disease ◽  
2020 ◽  
Author(s):  
Yue Lian Liu ◽  
Jian Rong Tang ◽  
Yu Han Zhou
Keyword(s):  
Disease Incidence ◽  
Morphological Characteristics ◽  
Pathogenicity Test ◽  
Sterile Water ◽  
Single Spore ◽  
First Report ◽  
Rdna Its ◽  
Colletotrichum Siamense ◽  
Monstera Deliciosa ◽  
Pure Cultures

Monstera deliciosa Liebm is an ornamental foliage plant (Zhen et al. 2020De Lojo and De Benedetto 2014). In July of 2019, anthracnose lesions were observed on leaves of M. deliciosa cv. Duokong with 20% disease incidence of 100 plants at Guangdong Ocean University campus (21.17N,110.18E), Guangdong Province, China. Initially affected leaves showed chlorotic spots, which coalesced into larger irregular or circular lesions. The centers of spots were gray with a brown border surrounded by a yellow halo (Supplementary figure 1). Twenty diseased leaves were collected for pathogen isolation. Margins of diseased tissue was cut into 2 × 2 mm pieces, surface-disinfected with 75% ethanol for 30 s and 2% sodium hypochlorite (NaOCl) for 60 s, rinsed three times with sterile water before isolation. Potato dextrose agar (PDA) was used to culture pathogens at 28℃ in dark. Successively, pure cultures were obtained by transferring hyphal tips to new PDA plates. Fourteen isolates were obtained from 20 leaves. Three single-spore isolates (PSC-1, PSC-2, and PSC-3) were obtained ,obtained, which were identical in morphology and molecular analysis (ITS). Therefore, the representative isolate PSC-1 was used for further study. The culture of isolate PSC-1 on PDA was initially white and later became cottony, light gray in 4 days, at 28 °C. Conidia were single celled, hyaline, cylindrical, clavate, and measured 13.2 to 18.3 µm × 3.3 to 6.5 µm (n = 30). Appressoria were elliptical or subglobose, dark brown, and ranged from 6.3 to 9.5 µm × 5.7 to 6.5 µm (n = 30). Morphological characteristics of isolate PSC-1 were consistent with the description of Colletotrichum siamense (Prihastuti et al. 2009; Sharma et al. 2013). DNA of the isolate PSC-1 was extracted for PCR sequencing using primers for the rDNA ITS (ITS1/ITS4), GAPDH (GDF1/GDR1), ACT (ACT-512F/ACT-783R), CAL (CL1C/CL2C), and TUB2 (βT2a/βT2b) (Weir et al. 2012). Analysis of the ITS (accession no. MN243535), GAPDH (MN243538), ACT (MN512640), CAL (MT163731), and TUB2 (MN512643) sequences revealed a 97-100% identity with the corresponding ITS (JX010161), GAPDH (JX010002), ACT (FJ907423), CAL (JX009714) and TUB2 (KP703502) sequences of C. siamense in GenBank. A phylogenetic tree was generated based on the concatenated sequences of ITS, GAPDH, ACT, CAL, and TUB2 which clustered the isolate PSC-1 with C. siamense the type strain ICMP 18578 (Supplementary figure 2). Based on morphological characteristics and phylogenetic analysis, the isolate PSC-1 associated with anthracnose of M. deliciosa was identified as C. siamense. Pathogenicity test was performed in a greenhouse at 24 to 30oC with 80% relative humidity. Ten healthy plants of cv. Duokong (3-month-old) were grown in pots with one plant in each pot. Five plants were inoculated by spraying a spore suspension (105 spores ml-1) of the isolate PSC-1 onto leaves until runoff, and five plants were sprayed with sterile water as controls. The test was conducted three times. Anthracnose lesions as earlier were observed on the leaves after two weeks, whereas control plants remained symptomless. The pathogen re-isolated from all inoculated leaves was identical to the isolate PSC-1 by morphology and ITS analysis, but not from control plants. C. gloeosporioides has been reported to cause anthracnose of M. deliciosa (Katakam, et al. 2017). To the best of our knowledge, this is the first report of C. siamense causing anthracnose on M. deliciosa in ChinaC. siamense causes anthracnose on a variety of plant hosts, but not including M. deliciosa (Yanan, et al. 2019). To the best of our knowledge, this is the first report of C. siamense causing anthracnose on M. deliciosa, which provides a basis for focusing on the management of the disease in future.

scholarly journals Rhizoctonia solani AG-1 IA infects both rice and signalgrass in the Colombian Llanos

2016 ◽  
Vol 46 (1) ◽  
pp. 65-71 ◽  
Author(s):  
Lina Maria Ramos-Molina ◽  
Edisson Chavarro-Mesa ◽  
Danilo Augusto dos Santos Pereira ◽  
María del Rosario Silva-Herrera ◽  
Paulo Cezar Ceresini
Keyword(s):  
Rhizoctonia Solani ◽  
Species Complex ◽  
Molecular Detection ◽  
Sheath Blight ◽  
Pathogenicity Test ◽  
Rice Sheath Blight ◽  
Specific Primers ◽  
5.8S Rdna ◽  
Foliar Blight ◽  
Rhizoctonia Oryzae

ABSTRACT Foliar blight and death of signalgrass (Urochloa spp.) pastures are caused by the Rhizoctonia solani fungus. This study aimed at determining which pathogens from the Rhizoctonia species complex are associated with leaf and sheath blight in Urochloa and rice, in the Colombian Llanos. Sympatric areas of Urochloa pastures adjacent to rice cropping areas were sampled using a linear transect system. The pathogens were identified using morphological traits, molecular detection based on specific primers and sequencing of the ITS-5.8S rDNA region. R. solani AG-1 IA predominated as the pathogen associated with foliar blight in all samples from U. brizantha cv. 'Toledo' and hybrid Urochloa cv. 'Mulato'. Besides R. solani AG-1 IA (18 % of the samples), Rhizoctonia oryzae-sativae (71 %) and Sclerotium hydrophilum (11 %) were also detected. In the cross-pathogenicity test, the R. solani AG-1 IA fungus was the most aggressive to Urochloa, while R. oryzae-sativae produced very mild infection symptoms. This is the first report of R. oryzae-sativae and S. hydrophilum associated with the complex of rice sheath blight diseases in Colombia.

Response of prolonged storage time and growth media on seedling emergence of onion (Allium cepa L.) in South Africa

2018 ◽  
pp. 33-40
Author(s):  
K.E. Lodama ◽  
A.S. Gerrano ◽  
S.M. Laurie ◽  
S. Mavengahama ◽  
P.O. Adebola
Keyword(s):  
South Africa ◽  
Allium Cepa ◽  
Storage Time ◽  
Seedling Emergence ◽  
Prolonged Storage ◽  
Growth Media ◽  
Allium Cepa L

scholarly journals First Report of Stem and Foliar Blight of Sunflower Caused by Alternariaster helianthi in Louisiana

Plant Disease ◽  
2012 ◽  
Vol 96 (5) ◽  
pp. 761-761 ◽  
Author(s):  
R. Singh ◽  
D. M. Ferrin
Keyword(s):  
Disease Incidence ◽  
Fluorescent Light ◽  
Infected Leaf ◽  
Stem Tissue ◽  
First Report ◽  
Foliar Blight ◽  
Leaf Spots ◽  
Plastic Bags ◽  
Alternaria Helianthi ◽  
Stem Lesions

During the fall of 2009, sunflower (Helianthus annuus L.) planted at the LSU AgCenter's Burden Center in Baton Rouge, LA exhibited severe stem and foliar blight symptoms. Symptoms on stems and petioles included elongated, slightly sunken lesions with dark brown margins. Leaf symptoms included irregular to circular, dark brown lesions with white centers and surrounded by a yellow halo. Several spots often coalesced to form large, blighted areas, and severely affected leaves turned yellow, followed by defoliation. The corolla and calyx exhibited similar lesions except for the yellow halo. Disease developed rapidly and the whole (100% disease incidence) field was blighted within a week following a rain (4 mm). Infected leaf and stem tissue was surface disinfested and plated on ¼-strength potato dextrose agar (PDA). Both leaf and stem tissue consistently produced dark olivaceous-to-black fungal colonies at room temperature under 12 h of fluorescent light per day. Conidia were 53 to 128 × 10 to 26 μm, borne singly on the conidiophores, hyaline to dark olivaceous, cylindrical, rounded at both ends, and with 6 to 10 transverse and 0 to 2 longitudinal septa. Conidiophores were single, unbranched, septate, hyaline to dark olivaceous, and measured 77 to 128 × 7 to 13 μm. Morphologically, the fungus was identified as Alternariaster helianthi (Hansf.) E.G. Simmons (= Alternaria helianthi [Hansf.] Tubaki & Nishih) (1). A single-spore isolate (PDC-4291) was obtained from the original culture and DNA from this isolate was extracted with a DNeasy Plant Mini Kit (Qiagen Inc., Valencia, CA). Primers ITS1 and ITS4 were used to amplify and sequence the internal transcribed spacer regions 1 and 2, and NCBI blast analysis of the 552-bp sequence (GenBank Accession No. JN208925) resulted in 100% homology with Alternaria helianthi isolated from sunflower infected with leaf spot and blight disease in India (GenBank Accession No. DQ156343). Pathogenicity was determined by inoculating 20 potted sunflower plants (Full Sun Improved TD, Fred C. Gloeckner and Company, Inc., Harrison, NY) with conidia from a 2-week-old culture of isolate PDC-4291. Each plant was sprayed with 25 ml of suspension containing 106 conidia/ml. Twenty control plants were sprayed with 25 ml of sterile distilled water. Inoculated and control plants were covered with plastic bags and maintained in a greenhouse at 28 ± 2°C. Plastic bags were removed 72 h after inoculation. Leaf spots similar to the original symptoms appeared on all 20 inoculated plants 5 days after inoculation. A few stem lesions were observed on 13 plants. Two weeks after inoculation, infected leaves turned yellow and blighted. Alternariaster helianthi (= Alternaria helianthi) was reisolated from the leaf spots and stem lesions. No symptoms developed on any of the 20 control plants. On the basis of morphology and sequence data, this pathogen was identified as A. helianthi, and to our knowledge, this is the first report of sunflower stem and foliar blight caused by A. helianthi in Louisiana. In Louisiana, sunflower is a popular ornamental that is grown in landscapes and gardens and by commercial flower growers who grow it for cut flower arrangements. Louisiana's hot, humid weather is ideal for disease development, which may discourage gardeners and commercial growers from planting sunflower. Reference: (1) E. G. Simmons. Alternaria: An Identification Manual. CBS Fungal Biodiversity Center, Utrecht, the Netherlands, 2007.

scholarly journals First Report of Raceme Blight Caused by Cladosporium cladosporioides on Macadamia Nuts in South Africa

Plant Disease ◽  
2008 ◽  
Vol 92 (3) ◽  
pp. 484-484 ◽  
Author(s):  
N. van den Berg ◽  
S. Serfontein ◽  
B. Christie ◽  
C. Munro
Keyword(s):  
South Africa ◽  
Developmental Stages ◽  
Plant Protection ◽  
Cladosporium Cladosporioides ◽  
First Report ◽  
Small Water ◽  
Plastic Bags ◽  
Severe Infections ◽  
Branched Chains ◽  
Rat Tail

In September of 2005 and 2006, macadamia (Macadamia integrifolia Maiden & Betche) orchards in Tzaneen, Modjadji, Politsi, and Levubu in the Northern Province and Kiepersol in Mpumalanga, South Africa were surveyed and sampled to determine the causal agent of raceme blight. Symptoms appeared during early bloom and were present on racemes of all developmental stages. Early signs were necrotic tips of the peduncle that often curved to one side with necrosis spreading upward, resulting in the so-called “rat tail”. Unopened flowers were also affected. In severe cases, the entire inflorescence (flowers and peduncle) was necrotic and eventually flowers abscised. Occasionally, infection began with single flowers as small water-soaked specks on the flower, with no symptoms on the green peduncle. Diseased racemes were covered with olive gray patches of mycelia and abundant conidia. Flowers with blight symptoms were collected, surface disinfested with 70% ethanol for 2 min, and left to dry. Thirty isolations were made from the interface of the lesion and healthy tissue, plated onto 50% potato dextrose agar (PDA) (Biolab, Merck Laboratories, Wadeville, South Africa) with 19 g of agar per liter, and incubated at 25°C for 5 days. Direct isolations from diseased material were done by picking up conidia and placing them on PDA. A fungus was isolated consistently and identified morphologically as Cladosporium cladosporioides (Fresen.) de Vries based on the velvety olive-brown with almost black reverse colony color and dimensions and color of conidia and conidiophores. Conidia formed in long branched chains that readily disarticulate, mostly aseptate, elliptical to limoniform, 3 to 10.5 (3 to 7) × 2 to 5 (3 to 4) μm. Conidia were pale to olive brown and smooth to verruculose. Ramoconidia were 0-1 septate, 2.5 to 5 μm wide, up to 28 μm long, smooth or sometimes minutely verruculose. Conidiophores were pale to olive brown, macro- and micronemateus, smooth or sometimes verruculose, and of various lengths up to 320 μm long and 2 to 6 μm wide. To confirm pathogen identity, the ITS 1 and ITS 4 regions were sequenced, which had 100% homology to the 18S rRNA of C. cladosporioides (GenBank Accession No. DQ 124142.1). Pathogenicity trials were conducted in the field. Fungal isolates were grown on PDA for 6 days, spores were harvested, and a suspension was made (106 spores ml–1). Twenty macadamia inflorescences (cv. Beaumont) were dipped in the suspension for 1 s, covered with plastic bags containing wet cotton wool, and covered with paper bags. Inflorescences in different stages (petal fall, knee stage, and closed) were inoculated. Control treatments were dipped in sterile water. After 2 to 3 days, the bags were removed. Symptoms developed on all 20 inflorescences and in all cases, the bottom of the inflorescence blighted, resulting in the typical rat tail symptom. C. cladosporioides was reisolated from all surface-disinfested infected material plated on PDA. Control inflorescences developed no symptoms. Isolate PPRI 8376 was deposited with the National Collection of Fungi, Plant Protection Research Institute, Pretoria, South Africa. The disease is prevalent during wet periods and 5 to 10% of flowers were infected. The disease has increasingly been seen in orchards over the last two seasons and under favorable wet, humid conditions, severe infections have resulted in 100% flower loss. To our knowledge, this is the first report of C. cladosporioides causing raceme blight on macadamia in South Africa.

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