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African Journal of Food, Agriculture, Nutrition and Development
Rural Outreach Program
ISSN: 1684-5358
EISSN: 1684-5374
Vol. 12, No. 7, 2012, pp. 7072-7087
Bioline Code: nd12110
Full paper language: English
Document type: Research Article
Document available free of charge

African Journal of Food, Agriculture, Nutrition and Development, Vol. 12, No. 7, 2012, pp. 7072-7087

 en MORPHOLOGICAL CHARACTERIZATION AND IDENTIFICATION OF Phytophthora check for this species in other resources SPECIES CAUSING CITRUS GUMMOSIS IN KENYA
Mounde, LG; Ateka, EM; Kihurani, AW & Wasilwa, L

Abstract

Frequent outbreaks of citrus gummosis in Kenyan citrus orchards have been reported, yet the identity and distribution of the Phytophthora check for this species in other resources species causing the disease are unknown. Work was carried out to (i) characterize and identify Phytophthora species associated with citrus gummosis based on cultural and morphological traits and (ii) determine the distribution of these species associated with gummosis in different agroecological zones (AEZ). Some 59 plant and soil samples obtained from symptomatic trees and the rhizosphere were evaluated by direct isolation and baiting, respectively, using Phytophthora semi-selective media. Phytophthora species were identified on the basis of colony morphology, mycelial characteristics, cardinal growth temperatures, morphology and dimensions of sporangia, oogonia and antheridia. For colony morphology and growth temperature studies, a 5 mm diameter mycelial plug of each isolate was transferred to amended cornmeal agar (ACMA) and incubated at 5, 24 and 35°C for 7 days in the dark. Growth rates were evaluated based on daily records of mycelial growth for 7 days. The occurrence and distribution of these species were determined by recording the number of isolates recovered from samples from each AEZ. P. citrophthora check for this species in other resources was the most prevalent (76.3 %) of all the Phytophthora species identified in all the AEZs, followed by P. nicotianae check for this species in other resources (22 %). P. syringae check for this species in other resources was the least (1.7 %) prevalent. P. citrophthora was the only species present in all AEZs sampled whereas P. nicotianae was confined to the coastal lowlands although also present in other zones in a lower scale. P. syringae was present only in low midland zones and was the only species not found in coastal lowland zones. The forty five isolates of P. citrophthora, thirteen isolates of P. nicotianae and one isolate of P. syringae were tested for virulence on fruits of lemon var. rough lemon. The three most virulent isolates of P. citrophthora, two most virulent isolates of P. nicotianae and the only isolate of P. syringae were selected for pathogenicity testing on lemon seedlings. Based on these studies, it may be concluded that P. citrophthora, P. nicotianae (syn. P. parasitica) and P. syringae are the Phytophthora species associated with citrus gummosis in Kenya. Molecular characterization of the pathogens is recommended to confirm true genetic identity of the species.

Keywords
Phytophthora, morphological, characterization, virulence, pathogenicity

 
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