Browsing by Author "Vicent, A."
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Item Characterization of Mycosphaerellaceae species associated with citrus greasy spot in Panama and Spain(PLoS ONE, 2017-12) Aguilera-Cogley, V.A.; Berbegal, M.; Català, S.; Brentu, F.C.; Armengol, J.; Vicent, A.Greasy spot of citrus, caused by Zasmidium citri-griseum (= Mycosphaerella citri), is widely distributed in the Caribbean Basin, inducing leaf spots, premature defoliation, and yield loss. Greasy spot-like symptoms were frequently observed in humid citrus-growing regions in Panama as well as in semi-arid areas in Spain, but disease aetiology was unknown. Citrus-growing areas in Panama and Spain were surveyed and isolates of Mycosphaerellaceae were obtained from citrus greasy spot lesions. A selection of isolates from Panama (n = 22) and Spain (n = 16) was assembled based on their geographical origin, citrus species, and affected tissue. The isolates were characterized based on multi-locus DNA (ITS and EF-1α) sequence analyses, morphology, growth at different temperatures, and independent pathogenicity tests on the citrus species most affected in each country. Reference isolates and sequences were also included in the analysis. Isolates from Panama were identified as Z. citri-griseum complex, and others from Spain attributed to Amycosphaerella africana. Isolates of the Z. citri-griseum complex had a significantly higher optimal growth temperature (26.8°C) than those of A. africana (19.3°C), which corresponded well with their actual biogeographical range. The isolates of the Z. citri-griseum complex from Panama induced typical greasy spot symptoms in ‘Valencia’ sweet orange plants and the inoculated fungi were reisolated. No symptoms were observed in plants of the ‘Ortanique’ tangor inoculated with A. africana. These results demonstrate the presence of citrus greasy spot, caused by Z. citri-griseum complex, in Panama whereas A. africana was associated with greasy spot-like symptoms in Spain.Item Crop loss, aetiology and epidemiology of citrus black spot in Ghana(Springer, 2012-01) Brentu, F.C.; Oduro, K.A.; Offei, S.K.; Odamtten, G.T.; Vicent, A.; Peres, N.A.; Timmer, L.W.Citrus Black Spot (CBS), caused by Guignardia citricarpa, was detected for the first time in Ghana and in West Africa. The disease was first observed in the Eastern Region in 1999 with typical disease symptoms including hard spot, virulent spot and false melanose were observed on several citrus species. A survey revealed that the disease has reached epidemic levels in the citrus-producing areas of the Eastern and Ashanti regions and is spreading rapidly within these areas and to other regions of the country. Currently, CBS is the most important fruit disease of citrus in Ghana, causing about 22% crop loss. Although the disease does not cause postharvest decay and the internal quality of the fruit is not affected, significant amounts of blemished fruit are discarded at the markets. Disease incidence and severity was found to be higher on mature than on young citrus trees. Pycnidia were found on fruit with hard spot symptoms, and pycnidia and pseudothecia typical of Guignardia spp. were found on decomposing leaves. Two species, G. citricarpa and G. mangiferae, were isolated from 15% of the samples collected and identified using the Oatmeal Agar test and by PCR with species-specific DNA primers. Isolates of G. citricarpa produced CBS symptoms after 80 to 233 days on 75% of the artificially inoculated young fruit of Valencia Late sweet orange. The fungus was re-isolated from symptomatic, inoculated fruit completing Koch’s postulates. Isolates of the endophyte G. mangiferae did not induce symptoms in the pathogenicity tests. In epidemiological studies, infections were detected from November to February for the minor cropping season and from May to November for the major season. Fruit of Valencia Late sweet orange were susceptible to G. citricarpa infection for up to 7 months after petal fall. Knowledge of the disease cycle in Ghana will improve methods for disease control.Item First report of Pseudocercospora angolensis causing fruit and leaf spot of citrus in Ghana(Plant Disease, 2013-12) Brentu, F.C.; Cornelius, E.W.; Lawson, L.E.V.; Oduro, K.A.; Vicent, A.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).Item Gummosis of citrus in Ghana caused by Phytophthora citrophthora(Australasian Plant Disease Notes, 2015-12) Brentu, F.C.; Vicent, A.Citrus in Ghana are seriously affected by gummosis, which causes trunk cankers and tree death. The disease was originally related to Phytophthora parasitica but more recently to Lasiodiplodia theobromae. The aetiology of citrus gummosis in Ghana was reassessed in the same locations surveyed by previous studies. Phytophthora citrophthora was confirmed as the causal agent of the disease. (PDF) Gummosis of citrus in Ghana caused by Phytophthora citrophthora. Available from: https://www.researchgate.net/publication/284091173/download [accessed Sep 05 2018].