First Report of Leaf Blight of Taro (Colocasia esculenta) Caused by Phytophthora colocasiae in Ghana

Abstract

Taro (Colocasia esculenta (L.) Schott) is an important food crop cultivated for its edible tubers in Ghana. In May 2009, outbreaks of a destructive leaf disease were observed on several taro farms in the Atiwa, East-Akim, Fanteakwa, West-Akim, and New Juaben districts of the Eastern Region of Ghana. Symptoms began on leaves as small, brown, water-soaked lesions that enlarged and coalesced into large lesions with yellow exudate, ultimately leading to the defoliation and death of plants. Symptoms were suggestive of taro leaf blight (TLB) caused by Phytophthora colocasiae Raciborski (3). By August 2010, the disease had spread to other taro-growing regions in Ghana. To identify the pathogen, leaf tissue from lesion margins were excised and plated on carrot agar and V8 selective media for Phytophthora and incubated at 27°C for 5 days (2). Growth from diseased tissue was used for morphological characterization. Sporangia were ovoid, hyaline, papillate, caducous, 30 to 60 × 17 to 28 μm, and pedicels were 3.5 to 10 μm long. Genomic DNA was isolated from pure cultures of two isolates, PCg11-2 from Oseim (6°15′N, 0°27′E) and PCg11-5 from Oyoko (6°8′N, 0°17′W). Ribosomal DNA ITS1, 5.8S and ITS2 were amplified by PCR using the ITS1 and ITS4 primers (4). The resultant 784-bp amplicons were sequenced (GenBank Accession Nos. JN662439 and JN662440). Sequences of both isolates were identical. A BLASTn search of these sequences revealed maximum homology of 99% with the sequence of P. colocasiae strains from blighted taro leaves in Nigeria (GenBank Accession No. HQ602756), Hawaii (GenBank Accession No. GU258997), and several strains in Asia and the South Pacific. On the basis of morphological characteristics and nucleotide homology, the isolates were identified as P. colocasiae. To fulfill Koch's postulates, 30 leaf discs from 3-month-old plants were inoculated with 10 μl of a suspension of 3 × 105 zoospores per ml (2). Leaf discs were incubated in the dark at 27°C on wet foam in plastic trays for 5 days. All inoculated discs developed blight symptoms similar in appearance to those observed on diseased taro in the fields. Control discs remained asymptomatic. P. colocasiae was reisolated from leaf discs and its identity confirmed by morphological characteristics. To our knowledge, this is the first report of TLB and P. colocasiae in Ghana. Occurrence of TLB was recently reported in Nigeria (1). The recent occurrence of TLB in both Nigeria and Ghana threaten the taro-growing regions of West and Central Africa. Disease surveys and a management strategy that includes resistant varieties are urgently needed. References: (1) R. Bandyopadhyay et al. Plant Dis. 95:618, 2011. (2) A. Drenth and B. Sendall. Practical Guide to Detection and Identification of Phytophthora. Version 1.0. CRC for Tropical Plant Protection. Brisbane, Australia, 2001. (3) M. Raciborski. Java Batavia Bull. 19:189, 1900. (4) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, CA, 1990.

Taro Leaf Blight—A Threat to Food Security

“…There is concern for food security and social unrest. The disease has spread rapidly to other countries in West Africa, including Nigeria and Ghana [17,18]. While it is too early to assess the impact of TLB on these countries, experience tells us that the disease has a potential to create a devastating cascade effect: reduction in food and household incomes, increased poverty and even starvation.…”

“…The Oomycete is now widely distributed geographically over almost all continents including Asia (Bangladesh, Brunei, China, India, Indonesia, Irian Jaya, Japan, Korea, Malaysia, Peninsular Malaysia, Myanmar, Nepal, Pakistan, Philippines, Sri Lanka, Taiwan, Thailand), Africa (Cameroon, Equatorial Guinea, Ethiopia, Ghana, Nigeria, Seychelles), North America (USA), Central America and Caribbean (Brazil, Cuba, Dominican Republic, Puerto Rico, Trinidad and Tobago), South America (Argentina), Oceania (American Samoa, Guam, Northern Mariana Islands, Palau, Papua New Guinea, Samoa, Solomon Islands) [17,18,56,57]. Some of these reports have not been verified and need confirmation.…”

“…The introduction of TLB to the Caribbean in 2004 led to the annihilation of the taro crop in the Dominican Republic, Cuba and Puerto Rico [1]. Most recently TLB has been reported from West Africa in Cameroon [16], Nigeria [17] and Ghana [18] where it continues to decimate taro cultivation, and is impacting on the livelihoods and food security of rural communities. A number of other countries in West and Central Africa may face the same problem because the disease has the capacity to spread on taro planting material-the Oomycete has been reported to survive on planting tops for up to 3 weeks after harvest [19].…”

Conserving and Sharing Taro Genetic Resources for the Benefit of Global Taro Cultivation: A Core Contribution of the Centre for Pacific Crops and Trees

“…With the recent TLB outbreak and spread in West Africa, in Nigeria, 37 the global leader in taro production, and Ghana, 38 also among the top five global producers, access to TLB-resistant germplasm became vital. However, introducing new allelic diversity of taro globally is not only relevant for TLB resistance breeding but also for better adaptation to abiotic stresses exacerbated by climate change.…”

Characterization of Isolates of Phytophthora colocasiae Collected from Andhra Pradesh and Telangana Causing Leaf Blight of Taro

“…after release and size of the cyst was 9.7 µm to 19.5 µm in diameter. Omane et al, (2012) reported morphological characters of P. colocasiae isolates of taro from Ghana. Sporangia were ovoid, hyaline, papillate, caduceus, 30 to 60 µm × 17 to 28 µm, and pedicels were 3.5 µm to 10 µm long.…”