First Report of Pseudocercospora angolensis Causing Fruit and Leaf Spot of Citrus in Ghana

Abstract

Citrus is one of the most important crops in Ghana, representing a large proportion of the fresh fruit consumed in the country. In 2004, symptoms consisting of necrotic leaf spots of about 1 cm in diameter with light brown centers and dark brown margins surrounded by a yellow halo were first observed in sweet orange (Citrus sinensis) and mandarin (C. reticulata) orchards in the Eastern Region of Ghana. Fruits with raised corky lesions of up to 3 to 4 cm in diameter with yellow halos were also observed. Affected fruit had longitudinal and transversal cracks in the rind with the internal locules exposed. Juice content in diseased fruit was strongly reduced, making them unsuitable for fresh consumption or processing. The disease expanded to the Central and Ashanti Regions, with incidences over 95% and estimated yield losses of about 50 to 90%. Symptomatic leaves and fruit collected in Kade in the Eastern Region were surface disinfested with 0.5% NaOCl for 5 min and small fragments from lesions were plated onto malt extract agar (MEA). Slow-growing fungal colonies were isolated from about 5% of the affected tissues plated after 5 days of incubation at 24 to 26°C, and were transferred to V-8 juice agar and MEA. Plates were incubated for 30 days at 24 to 26°C with 12 h of fluorescent light and 12 h of dark for morphological examination. Colonies were gray in the upper side and dark green on the underside. Conidia produced in culture were mostly solitary or in short chains of 2 to 6 spores, hyaline to pale brown, cylindrical, with rounded apex and base truncated. Conidia were 24 to 82 × 4 to 6 μm, with up to 3 to 5 transverse septa and no longisepta. The 5.8S, ITS2, and 28S ribosomal RNA (rRNA) regions were amplified using the primers ITS1 and ITS4 (3) and sequenced from DNA extracted from the isolate MC-39, obtained from sweet orange leaves in Kade (GenBank Accession No. KF111755). The sequence had 99% identity (total score 819, 85% coverage) with that of Pseudocercospora angolensis (T. Carvalho & O. Mendes) Crous & U. Braun epitype strain CBS 112933 (GU269836) (1). Pathogenicity tests were performed twice on 12-week-old detached fruit of sweet orange cv. Valencia Late of about 4 to 5 cm in diameter. Inoculations were performed using a conidial suspension (3.0 × 105 conidia/ml water) by spraying fruit to run off, brushing the rind, dipping for 6 min, or injecting 2 ml in the albedo. Twenty-two isolates were evaluated and 18 fruit were used for each inoculation technique, isolate and experiment. Fruit treated with sterile distilled water were used as controls. Inoculated fruit were maintained in humid chambers at 24 to 26°C. Disease incidence on inoculated fruit varied from 40.7% to 92.6% and severity from 2 to 3 to 3 to 11 lesions per fruit, depending on the isolate and inoculation technique. No symptoms were observed on control fruit. Fungal colonies morphologically identified as P. angolensis were reisolated from lesions on inoculated fruit, but not from asymptomatic control fruit. Based on these results, the disease was identified as Pseudocercospora fruit and leaf spot of citrus caused by P. angolensis. Until this present report, Ghana was considered one of the few countries in Central Africa that was still free of this citrus disease (2). References: (1) P. W. Crous et al. Stud. Mycol. 75:37, 2013. (2) A. A. Seif and R. J. Hillocks. Int. J. Pest Manag. 39:44, 1993. (3) T. J. White et al. Pages 315-322 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990.

Spatial Organisation Influences Citrus <i>Pseudocercospora</i> Leaf and Fruit Spot Disease Severity in Cocoa-Based Agroforestry Systems

“…Since 1952, this pathogen is a major limiting factor to Citrus spp. production in some 23 African countries and Yemen [5] [6] [7]. Because of traditional trade of plant material in these countries and the wind-borne nature of the fungal spores, this disease constitutes a potential threat [8].…”

Mycobiota Associated with the Vascular Wilt of Poplar

“…de Candolle, Prodr. in India [ 129 ], Alatospora has been recorded from aquatic habitats [ 130 ], Amesia nigricolor has been recorded from an indoor habitat in India [ 131 ], Cercospora beticola from sugar beet leaves, Desmazierella acicola from pine needle litter [ 132 , 133 ], Dissoconium eucalypti from Eucalyptus leaf [ 134 ], Halokirschsteiniothelia maritima from decaying wood in Thailand [ 135 ], Nigrospora oryzae from tropical plants [ 136 ], Pleurophoma ossicola from bone [ 102 ], Pseudocercospora angolensis from leaf spot on Citrus in Africa [ 137 ], Sakaguchia lamellibrachiae (Nagah., Hamam., Nakase and Horikoshi) Wang, Bai, Groenew. and Boekhout from a deep-sea tubeworm in Japan [ 138 ], and the basidiomycetous yeast Erythrobasidium hasegawianum has been recorded from old beer yeast culture in USA [ 139 ].…”

Development of loop-mediated isothermal amplification (LAMP) assay for detection of Pseudocercospora angolensis in sweet orange

“…That explains why in this study, the ITS1, 5.8S, ITS2 and partial sequence of the large subunit ribosomal RNA in the genome of P. angolensis were used to design both PCR and LAMP primers. In other studies, the Tef1-α , ITS1 and ITS4 have been used to design PCR primers for P. angolensis detection [8, 9]. The Tef1-α region is widely used in P. angolensis genus phylogeny since it is highly informative at species level [23].…”

“…Traditional methods of plant pathogen detection are time consuming and tedious [7]. Molecular methods such as PCR have been used to detect P. angolensis [8, 9]. Despite the specificity and sensitivity of PCR, this method is expensive due to the cost of thermocyclers and consumables used, hence not very cost-effective in low-income nation settings [10].…”