Genetic dissection of root-mediated yield heterosis in melon ( Cucumis melo )

Heterosis, the superiority of hybrids over their parents, is a major genetic force associated with plant fitness and crop yield enhancement. We previously discovered and characterized root-mediated yield heterosis (RMYH) in melon ( Cucumis melo ) using a half-diallel population, derived from 20 diverse parents. In the current study we investigated the genetic architecture of RMYH using a segregating population derived from a selected F ₁ hybrid (HDA019) that consistently induced RMYH under several melon scion varieties and growing conditions. 78 recombinant inbred lines (RILs) and their test-crosses to both parents were analyzed in yield trials as rootstocks under a common commercial scion variety. The population displayed normal root-mediated yield distribution and transgressive segregation relative to the parents but none of the RILs equaled the superior performance of the F ₁ hybrid. RMYH of HDA019 was dissected to small effect QTLs showing mostly additive or dominant mode-of-inheritance and favorable QTL-alleles were contributed by both parents. Five consistent QTLs were selected and used to demonstrate the potential of root-mediated yield QTL pyramiding, and 20 combinations of QTL pairs and triplets supported the cumulative model for heterosis. Favorable QTLs alleles were introgressed to generate advanced QTL-backcross lines that were used for validation. This study provides first detailed genetic dissection of yield-related rootstock traits in cucurbits, highlighting rootstock breeding as an important underutilized route for improving yield and stress tolerance of crops.