Peleg, G. | Search bioRxiv

bioRxiv2026

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 F1 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 F1 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. Key messageRoot-mediated yield heterosis in melon was genetically dissected using grafting strategy, revealing additive QTLs from both parents of the mapping population. Rootstock breeding through pyramiding of favorable alleles is proposed as strategy for enhancing crop yield and stress tolerance.

plant biology↗

bioRxiv2026

Domestication reduces drought tolerance in watermelon through loss of root plasticity traits

Wild plants, particularly those native to xeric environments, are highly adapted to survive under harsh conditions. These adaptive strategies primarily ensure the successful transfer of genetic material to subsequent generations, often independently of fruit size or quality. In contrast, more than 10,000 years of domestication have shifted plant strategies away from survival-oriented traits toward increase in yield and fruit quality. In this study, we characterized both shared and divergent physiological traits contributing to drought tolerance in wild and domesticated watermelon genotypes. Specifically, we compared above- and belowground responses to water limitation in desert watermelon (Citrullus colocynthis) versus these in a watermelon cultivar (Citrullus lanatus). While aboveground responses to water scarcity were largely similar between the two genotypes, pronounced differences emerged belowground. Root biomass and surface area in the cultivated watermelon were predominantly concentrated in the upper soil layers. In contrast, desert watermelon displayed substantial root system plasticity under drought conditions. Although total root biomass remained largely distributed in the upper soil layers, root surface area shifted toward deeper soil layers, indicating enhanced water acquisition from deeper soil layers without additional biomass investment. These findings suggest that domesticated watermelon, despite originating from desert-adapted ancestors, has largely lost the capacity for dynamic root system adjustment in response to spatial and temporal variation in soil water availability.

plant biology↗