Genotype x environment interaction for establishment and precocity traits among elite cocoa (Theobroma cacao L.) hybrids in Ghana

Developing and releasing cocoa varieties take several years of testing bi-parental crosses within the cocoa production belt. A critical phase in these testing schemes is multi-location evaluation under farmers' production conditions to elucidate the adaptation of promising varieties. The genotype and genotype- by- environment interaction (GEI) of 25 recently developed cocoa hybrids were assessed for establishment and precocity traits including stem diameter (SD) growth, percentage survival (%S), and number of pods per tree (NP). A randomized complete block design with four replications across five contrasting environments was used to evaluate the 25 hybrids together with two standard varieties. Variations due to genotype, environment, and GEI were highly significant (p < 0.001) for all the traits, with mean square of environment being the largest followed by the main effects and the GEI had the least. The mean performance of the hybrids ranged from 72.25% in PA7 x GEBP 303/B-M to 88% in PA7 x CRG 0543 for % S, 31.93 in T79/501 x CRG 0543 to 40.87 mm in GU 144/C x EQX 78 for SD and 2.41 in T79/501 x CRG 0543 to 4.14 in GU 144/C x EQX 78 for NP. The genotype main effects plus genotype x environment interaction (GGE) biplot analysis revealed that hybrid 2 (GU 144 x EQX 78) performed best for SD growth and NP, and 12 (T63/967 x CRG 0314) for %S in most of the locations including Akomadan that had more intense dry seasons over the period. They could be used in cocoa breeding programs that seek to improve production under marginal conditions. Tafo for NP and SD growth, and Akomadan for % S were identified as the most discriminating and representative locations and considered the ideal testing locations for establishment and precocity traits. For stability, hybrids 3 (GU 144 x MAN 15-2), 7 (PA7 x EQX 78) and 17 (T63/967 x T65/238) were the best for NP, % S and SD growth, respectively. They were significantly not different from the highest performing hybrids for all the traits and could be further monitored for yield production before recommended as planting materials in Ghana and beyond.