African Journal of
Biotechnology

  • Abbreviation: Afr. J. Biotechnol.
  • Language: English
  • ISSN: 1684-5315
  • DOI: 10.5897/AJB
  • Start Year: 2002
  • Published Articles: 12184

Full Length Research Paper

Assessment of three cocoa hybrid families’ susceptibility and cysteine involvement in defense process against Phytophthora megakarya

Minyaka Emile
  • Minyaka Emile
  • Department of Biochemistry, Faculty of Sciences, University of Douala, P. O. Box 24157 Douala, Cameroon.
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Simo Claude
  • Simo Claude
  • Department of Plant Biology, Faculty of Sciences, University of Douala, P. O. Box 24157 Douala, Cameroon.
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Mouen Piau Jean Cyrille
  • Mouen Piau Jean Cyrille
  • Department of Biochemistry, Faculty of Sciences, University of Douala, P. O. Box 24157 Douala, Cameroon.
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Madina Banen Colette Vanessa
  • Madina Banen Colette Vanessa
  • Department of Biochemistry, Faculty of Sciences, University of Douala, P. O. Box 24157 Douala, Cameroon.
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Djocgoue Pierre François
  • Djocgoue Pierre François
  • Laboratory of Plant Physiology and Biochemistry, Department of Biological Sciences, Higher Teacher’s Training College, P. O. Box 47, Yaoundé, Cameroon.
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Omokolo Ndoumou Denis
  • Omokolo Ndoumou Denis
  • Laboratory of Plant Physiology and Biochemistry, Department of Biological Sciences, Higher Teacher’s Training College, P. O. Box 47, Yaoundé, Cameroon.
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  •  Received: 28 July 2017
  •  Accepted: 08 September 2017
  •  Published: 27 September 2017

Abstract

Black pod disease (BPD) is the major cocoa pathology constraint caused by an Oomycete, Phytophthora megakarya prevailing in African cocoa producing countries. The development of T. cacao planting material tolerant to BPD lies on cross-pollination of adequate parental genotypes which generate offspring with desirable traits. We assessed the susceptibility to BPD of offspring derived from three manual crosses (SNK13xUPA143, T79/501xUPA143 and UPA143xSNK64) using leaf discs test (LDT) which evaluates disease scores of hybrid genotypes. Cysteine involvement in T. cacao defence process against BPD has been studied for the potential use of this sulphur amino acid profile to identify tolerant cocoa hybrid genotypes. LDT displayed variable disease scores patterns. Within a given family, LDT revealed heterogeneity in disease scores. This heterogeneity may have been derived from polygenic character of T. cacao susceptibility to BPD. In SNK13xUPA143 family, 26.13% exhibited disease scores lower than two (tolerant hybrid genotypes). T79/501xUPA143 and UPA143xSNK64 generated 21.18 and 26.46% of tolerant hybrid genotypes respectively. This variability between families may have resulted from deferential susceptibility of parental clones; UPA143 being more susceptible than T79/501 followed by SNK13. SNK64 was the less susceptible to BPD. The percentages of tolerant hybrid genotypes in this study appeared to be consistent hence, SNK13xUPA143, T79/501xUPA143 and UPA143xSNK64 could be used to produce hybrids genotypes tolerant to BPD. Cysteine analysis was performed in none detached healthy and wounded-infected leaves of hybrid genotypes with variable disease scores. It appeared that cysteine was mobilized during the infection. Two main patterns were observed: in tolerant hybrid genotypes (disease score lower than 2), infection was associated to a significant reduction of cysteine content in young leaves while in susceptible hybrid genotypes, infection was associated to an increase (accumulation) of cysteine in young leaves. Cysteine could be involved in the synthesis of effective defence molecules against P. megakarya in tolerant hybrid genotypes. This set of finding may indicate that cysteine profile could be used to discriminate tolerant from susceptible hybrid genotypes of T. cacao to P. megakarya. 

Key words: Cocoa tree, black pod disease, hybrids genotypes, tolerance, cysteine.