Spatial distribution of phenotypic and biotic traits in cassava fields across Sierra Leone

Limited information regarding the spatial distribution of key agronomic and biotic traits in cassava morphological types constrains targeted breeding, conservation and crop improvement efforts in Sierra Leone. This study aimed to assess the distribution of key agronomic traits of cassava morphological types on 276 smallholder farms in Sierra Leone during January 2022. Traits studied included apical leaf color, leaf color, leaf vein color, number of lobes, number of whiteflies and grasshoppers, cassava mosaic disease (CMD) severity, farm size and age of plants. A field survey involving 276 cassava farms distributed across the five regions of Sierra Leone was conducted in January 2022. Agronomic, pest and disease data were collected from 30 randomly selected plants per farm following WAVE harmonized protocols. Geographic Information System (GIS)-based geospatial analyses were used to generate spatial distribution maps, while analysis of variance and Pearson correlation analyses were used to examine relationships among traits, pest abundance and disease severity. The majority of the cassava morphological types assessed exhibited green apical leaf (65.3%), light green leaf (64.3%), green leaf vein (55.6%), and prominent foliar scar (53.5%) with seven lobes (62.6%). Whitefly and grasshopper had higher populations of seven whiteflies per plant and 12 grasshoppers per plant in the western and eastern regions, respectively; whereas, a few farms in the southern region had no whiteflies. The CMD infection was mainly through contaminated cuttings (99.2%), with cutting-derived plants exhibiting moderate CMD severity. Mean CMD severity significantly (P ≤ 0.05) varied with farm size, with high (4.29), medium (3.8) and low (2.94) CMD recorded in small (0-1 ha), medium (2-3 ha) and big (4-5 ha) farms, respectively. This study establishes the existence of useful phenotypic variability in the regional distribution of morphological traits that could be exploited for phenotypic selection for production, conservation, utilization, and/ or genetic improvement of the crop. Findings serve as useful guide for genotypic selection for production, conservation, utilization, and genetic improvement of cassava using existing phenotypic diversity.