International Journal of Agricultural Policy and Research
Vol.6 (2), pp. 7-20, February 2018
Available online at https://www.journalissues.org/IJAPR/
Article 17/ID/JPR006/14/ pages
Author(s) retain the copyright of this article. Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License.
Original Research Article
Guaiacol Peroxidase heritability in tolerance of cocoa (Theobroma cacao L.) to Phytophthora megakarya, agent of cocoa black pod disease
Claude Simo*1,4, Pierre François Djocgoue 2,4 Emile Minyaka 3,4, and Ndoumou Denis Omokolo4
1Department of Plant Biology, Faculty of Science, University of Douala, PO Box 24157 Douala, Cameroon.
2Department of Plant Biology, Faculty of Science, University of Yaoundé I, P.O. Box 812, Yaoundé, Cameroon.
3Department of Biochemistry, Faculty of Science, University of Douala, PO Box 24157 Douala, Cameroon.
4Laboratory of Plant Physiology, Department of Biological Sciences, Higher Teacher’s Training College, University of Yaoundé I, P.O. Box 47, Yaoundé, Cameroon.
Tel: (+237) 677 58 92 87;691 78 36 07
*Corresponding Author E-mail: simoclaude(at)yahoo.fr;simoclaude(at)univ-douala.com
Black pod disease (BPD) caused by Phytophthora megakarya is the main limiting factor of cocoa production in African countries. This pathogen is responsible of yield reductions of 30-80%. Developing cocoa genotypes tolerant to BPD is the way out to improve yield and cocoa sustainability. Plants exposed to biotic stresses adjust their physiology and metabolism (such as stress-related enzymes among which peroxidases). This study was focused on peroxidases activities and heritability of (POX) in two hybrid populations F13 (♀SNK13 x ♂T79/467) and F79 (♀T79/467 x ♂SNK13) subjected P. megakarya. The results show that more tolerants and more productive hybrid genotypes (F1307, F1314, F7902, F7928) and more tolerant genotypes (F1315, F1313, F7926, F7907) relative to the best parent in the soluble (S) and bound fractions (L) recorded a large amount of POX activity with small areas of necrotic lesion in contrast to less tolerant and productive genotypes (F1324, F1308, F7915 and F7919) which displayed lowest POX activities and largest areas of necrotic lesion. A negative and significant correlation (P <0.01) was observed between the development of necrosis and peroxidase activities. The profile of peroxidase isoforms (S) of the mesocarp of infected pods revealed the existence of a specific form (A2) after infection in tolerant genotypes T79 / 467, F7902, F7926, F1315 and F1307. This isoform is linked to tolerance. The heritability values of POX activity obtained in soluble fractions (S) in the F13 family (♀SNK13 x ♂T79 / 467) in the F79 family (♀T79 / 467 x ♂SNK13) were relatively high, they were 0.65 and 0.62 respectively. These high values show a strong additive variance in the transmission of tolerance to black pod disease. The manifestation of hybrid vigor and the heritability values of POX that have been inherited by the offspring indicate a good general aptitude for the combination of parental clones. The existing isoform (A2) in hybrid tolerant genotypes could be used to develop productive and tolerant genotypes for farmers.
Key words: Theobroma cacao, Phytophthora megakarya, black pod disease, heritability, tolerance, peroxidases