With increasing frequency and intensity of dry spells in the cocoa production zones of West Africa, strategies for mitigating impact of water stress on cocoa seedling survival are urgently required. We investigated the effects of applied potassium on biomass accumulation, physiological processes and survival of cocoa varieties subjected to water stress in pot experiments in a gauzehouse facility. Four levels of potassium (0, 1, 2, or 3 g/plant as muriate of potash) were used. Soil water stress reduced plant biomass accumulation (shoot and roots), relative water content (RWC), chlorophyll content and fluorescence. Leaf phenol and proline contents were increased under water stress. Additionally, compared to the well-watered conditions, soils under water stress treatments had higher contents of exchangeable potassium and available phosphorus at the end of the experimental period. Potassium applied under well-watered conditions reduced leaf chlorophyll content and fluorescence and increased leaf electrolyte leakage, but improved the growth and integrity of physiological functions under soil water stress. Potassium addition increased biomass partitioning to roots, improved RWC and leaf membrane stability, and significantly improved cocoa seedling survival under water stress. Under water stress, the variety with the highest seedling mortality accumulated the highest contents of phenol and proline. A significant effect of variety on plant physiological functions was observed. Generally, varieties with PA 7 parentage had higher biomass partitioning to roots and better seedling survival under soil moisture stress. Proportion of biomass partitioned to roots, RWC, chlorophyll fluorescence and leaf electrolyte leakage appear to be the most reliable indicators of cocoa seedling tolerance to drought.

This study investigated the growth and leaf metabolism of clonal cocoa varieties in response to field stress conditions during wet and dry seasons. It was hypothesized that clonal cocoa varieties differ in their growth, photochemical efficiency, relative water content and central carbon metabolism under seasonal field stress conditions. Fourteen cocoa clone varieties between 35 and 44 months after planting were evaluated. Using various standard procedures in the field and laboratory, the plants were assessed in both wet (as unstress condition) and dry (as stress condition) seasons field conditions. Soil moisture content, photochemical efficiency, relative water content, non‐structural carbohydrate, carbon, nitrogen, growth and pod numbers were measured and compared among the seasons. The clones conserved cellular water, and this manifested in high levels of relative water content. Photochemical efficiency reduced in most of the clonal cocoa varieties during the dry season. Soluble sugars, starch and non‐structural carbohydrate accumulated in the leaves of the plants during the dry season. The levels of carbon and nitrogen were significantly high and low respectively in the dry season. Some clonal cocoa varieties increased growth rate and had a greater number of pods. The correlation analysis revealed a relationship among non‐structural carbohydrate, growth and physiological traits. Clone varieties CRG 0132/105, CRG 0145/205, CRG 0314/102 and T65/238 were the most tolerant in response to field stress conditions, and this reflected in the accumulation of soluble sugars, starch and non‐structural carbohydrate, improved photosynthetic efficiency, conserved cellular water and enhanced growth rates and pod numbers agreeing to the hypothesis.

The use of better‐quality varieties is a critical necessity in any crop production system. The knowledge and usage of information regarding genetic parameter estimates would undeniably guarantee the success of any breeding program as regards variety development. The present study was therefore set up to gauge the level of genetic diversity among half‐sib robusta coffee families in yield and yield‐related traits, determine the relationship among key agronomic traits, and identify best‐performing robusta coffee genotypes. Twenty‐three half‐sib families and one standard variety were field‐planted in 2016 following a randomized complete block design with four replications and assessed for growth and yield traits over a 9‐year period. Significant ( p < 0.05) differences were found among the families for all traits except leaf chlorophyll fluorescence. With the exception of length of laterals and leaf chlorophyll fluorescence, moderate‐to‐high heritability estimates (0.42–0.75) were observed for all traits reflecting an encouraging outlook for selection to improve these traits in variety development. Our analysis also revealed that early year average yield may to some extent be a good proxy to select for yield in later years ( r = 0.92, p < 0.0001) or total yield ( r = 0.96, p < 0.0001). Exploiting these associations may likely facilitate the breeding process of the crop. Cluster analysis grouped the half‐sib families into two main groups that could guide parental selection and future hybridization efforts. Principal component (PC) analysis showed that stem diameter, plant height, span, number of laterals, cumulative yield, and first 3‐year average yield influenced the variation the most among the evaluated half‐sib families on the first PC axis. The top 26% of the half‐sib families based on cumulative yield (U17, U57, U41, U67, U62, U24) are recommended for further testing through ortet selection following cup quality determination, and disease and pest reaction assessment.