Performance of melon hybrids derived from parents of diverse geographic Origins

Genetic relatedness and phenotype are important factors that govern the expression of heterosis in hybrid progeny of many cross-pollinating plant species. Since this relationship is important but not well understood in melon (Cucumis melo L.), one monoecious and two andromonoecious melon lines of diverse Chinese [Peoples Republic of China (PRC)] origin were crossed to the andromonoecious U.S. Western Shipping market type ‘Top Mark' (TM) and the andromonoecious, highly branched line H-16 to determine parental combining ability and heterosis for five yield component traits in three test environments [open-field (USA), and energy-saving (PRC) and plastic greenhouses (PRC)]. Random amplified polymorphic DNA (RAPD)- and simple sequence repeat (SSR)-based genetic distances (GD) among and between parents (5) and their hybrids (6) were calculated and compared to phenotypic trait values. These germplasms were evaluated for lateral branch number (LBN), days to 50% flower (DF), fruit number and weight per plant, and fruit length:diameter (L:D) ratio in each of three test environments. General combining ability was significant for all characters, except for L:D in all locations, and LBN and DF in the plastic greenhouse environment. Both descriptors of difference (genetic marker and phenotype) were discriminatory, and provided similar assessments of relationships among parents and hybrids. Although dramatic performance differences were detected between parents and among F₁ hybrid progeny, a strong relationship between GD and heterotic effects was not consistently detected.