Effect of Essential Oils from Citrus Varieties on in vitro Growth and Sporulation of Phaeoramularia angolensis Causing Citrus Leaf and Fruit Spot Disease |
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Authors: | Jean Kuate Jacob Foko Sali Atanga Ndindeng Pierre Michel Jazet-Dongmo Eric Fouré François Damesse Bella-Manga Daniel Ducelier |
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Institution: | (1) Institute of Agricultural Research for development (IRAD), P.O. Box 2067, Yaounde, Cameroon;(2) University of Dschang/CARFOP, P.O. Box 409, Dschang, Cameroon;(3) University of Douala, Faculty of Sciences, P.O. Box 24157, Douala, Cameroon;(4) African Centre for Research in Bananas and Plantains (CARBAP), P.O. Box 832, Douala, Cameroon |
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Abstract: | Citrus leaf and fruit spot disease caused by Phaeoramularia angolensis is a serious production constraint in tropical Africa. In previous studies, essential oils extracted from fruit peels of
two tolerant varieties exhibited a strong antifungal activity in vitro against P. angolensis as compared to oils from susceptible ones. In order to investigate if the susceptibility of citrus varieties is associated
with the antifungal activity of their essential oils, some 22 varieties of different susceptibility levels (tolerant, susceptible
and highly susceptible) and belonging to different botanical groups were studied. Oils extracted from fruit peels were evaluated
for their activity against radial growth and sporulation using the poisoned food technique. The optimal doses for growth inhibition
and conidial reduction were 2500 and 1000 ppm, respectively. At these doses, radial growth and sporulation exceeded the untreated
control respectively for four and nine varieties suggesting that oils from these varieties promote fungal development. In
general, oils from the tolerant group were most effective in reducing radial growth irrespective of dose. The highly susceptible
group ranked first in reducing sporulation at dose 1000 ppm (45.93%) while at higher doses of about 2000–2500 ppm, oils from
the tolerant varieties could reduce sporulation up to 100%. The marked dose effect in reducing sporulation suggests that there
may be different compounds acting with changing dose. Botanically, oils from pummelo (Citrus maxima, tolerant group), were best in reducing radial growth (>87% inhibition) while those from grapefruits (C. paradisi, highly susceptible group) were most effective in reducing sporulation (>64% reduction). |
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Keywords: | citrus essential oils Phaeoramularia angolensis radial growth and sporulation |
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