Journal of Applied Biosciences (J. Appl. Biosci.) [ISSN 1997 - 5902]
Volume 36: 2332 - 2339. Published December 7, 2010.
Antixenosis as a mechanism of cocoa resistance to the cocoa mirid, Sahlbergella singularis (Hemiptera: Miridae).
K. F N’Guessan1*, Ph. Lachenaud2, and A. B. Eskes2
1Centre National de Recherche Agronomique (CNRA), BP 808 Divo, Côte d’Ivoire
2CIRAD-CP, TA 80, Avenue Agropolis, 34398, Montpellier Cedex 5, France
ABSTRACT
Objectives: The objectives of this study were to confirm the existence and heritability of mirid resistance in selected promising cocoa genotypes and to determine whether antixenosis is involved in the mechanism of resistance.
Methodology and results: Ten cocoa hybrids obtained from crosses between clones identified as susceptible or promising for resistance to the cocoa mirid, Sahlbergella singularis, in previous studies, because they sustained high or low damage in the field, were evaluated using a choice test in 2006 and 2007 for attractiveness to mirid in the laboratory. Nine parental clones among which 3 susceptible and 6 field resistant were also evaluated. The Catongo clone IFC372, susceptible to mirid, was included in the clone test. The choice test was based on comparison of attractiveness of fragments of twigs of the different cocoa genotypes vis-à-vis 4th instar mirid nymphs in large Petri dishes (16 cm diameter X 2 cm height). Fives 6 cm-long fragments of twigs with the same diameter and representing five different cocoa genotypes were placed end to end in the Petri dishes. The insects were allowed to feed on the fragments of twigs for 24 hours and the feeding lesions were counted in order to assess attractiveness of the different genotypes. The results showed significant differences (P<0.01) between the 9 parental clones with regard to mirid feeding lesions. Significant differences (P<0.01) were also revealed between the hybrids progenies. During both years, the susceptible parents (IFC5, ICS39 and UF667) were ranked susceptible in the choice test with 8 to 10 lesions. The hybrid obtained from a cross between the susceptible parents (ICS39XIFC5) was also ranked susceptible. The 4 promising parents (T79/501, UPA402, NA32, and PA150) and their hybrids progenies (T79/501XUPA402, PA150XNA32) were less attractive to the mirid nymphs in the laboratory with between 2 to 5 lesions.
Conclusion and application of the findings: The results obtained here indicate that antixenosis, based on feeding preference, may partly explain the level of mirid damage observed in the field. The results also indicated that antixenosis can be transmitted from the parents to the progenies. Moreover, the clones T79/501, UPA402, NA32, PA150 and T60/887 have been confirmed in the laboratory to be resistant to Sahlbergella singularis.
Key words: Cocoa, resistance, antixenosis, Sahlbergella singularis.
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