Mapping of the egusi seed trait locus (eg) and quantitative trait loci associated with seed oil percentage in watermelon

Abstract

The egusi watermelon (Citrullus lanatus) is popular in West Africa for its oil and protein-rich seed, which is consumed in soups and stews. The egusi phenotypic trait is controlled by a single recessive gene (eg) and is characterized by large seed size and fleshy, thick pericarp. An F2 mapping population was derived from Strain II (PI 279461) of the Japanese cultivar Yamato-cream with normal seed type and low seed oil percentage (SOP = 25.2%) and an egusi type from Nigeria [Egusi (PI 560023)] with high SOP (40.6%). Genetic analysis confirmed that the egusi seed trait is controlled by a single recessive gene (eg) and the location of the gene was mapped to 57.8 cM on linkage group (LG) 2, between markers NW0248325 and NW0250248. Four main quantitative trait loci (M-QTL) were identified for SOP in the population with the eg locus contributing 84% of the explained phenotypic variation (R2). A significant epistatic interaction (E-QTL) was identified between, the eg locus and an M-QTL on LG 9B. The present study reports the location of the eg locus responsible for the egusi seed trait in watermelon on LG 2 as well as M-QTL and E-QTL associated with SOP.