Evaluation of resistance in selected cocoa genotypes to the brown cocoa mirid, Sahlbergella singularis Haglund in Nigeria

The use of host-plant resistance is the most economic and ecologically Sound option for the control of the most important insect pest of cocoa, Sahlbergella singularis leaving no deleterious side effects on the produce and the environment. 44 genotypes comprising 24 hybrids and 20 clones were assessed for antixenosis whereas 25 and 28 genotypes were tested for antibiosis and tolerance, respectively. The brown cocoa mirids showed significant non-preference for genotypes T65/7xT57/22, T65/7xT9/15, P7xPa150, T5315xN38, T53/5xT12/11, T65/35xT30/13, F3 Amazon, T86/2xT16/17, T65/7xT53/8, T86/2xT65/35, T82/27xT16/17, T9/15, T12/5, T30/13, C77, T53/8, T53/5, EET59, Pa150. UF 676, Amaz`15-15, BE 10, SPEC54 and Pa107. Mind survival (antibiosis) was lowest in EET59 (28.7%) while it ranged from 52.2 to 67.8% in genotypes BE10, Amaz15-15, SPEC54, UF 676, P7xPa150, and Pa107. The indigenous clone N38 had the highest number of lesions of 12.2 in the field while EET59, IFC-5, Playa Alta, BE10, Amaz15-15 and SPEC54 had mirid lesions of 2.7, 3.3. 5.2, 5.3, 5.5 and 5.5; respectively. However. in terms of recovery from mirid damage and dieback progression which were important parameters assessed in tolerance, Clones ICSI, EET59, BE 10, Amaz15-15, SPEC54 and Pa 102 showed highest rate of recovery from mirid damage and lowest dieback progression. Clones UF 676, C77, Pa150 and F3 Amazon also showed moderate recovery from mirid damage with mean scores of 1.2, 2.3, 1.6, 1.4, 1.7, 1.4 and 1.5, respectively. UF 676, C77, Pa150 and F3 Amazon performed moderately well in terms of tolerance. Some of these genotypes such as BE10, Amaz15-15, SPEC54, UF 676, P7xPa150, and Pa107 were very consistent in all mechanisms of resistance tested and therefore adjudged as resistant cocoa genotypes. (C) 2008 Elsevier Ltd. All rights reserved.