Trait Architecture of Fruit-Panicle Economic Traits in Idesia polycarpa and Its Implications for Breeding

Idesia polycarpa is an important woody oil tree species in East Asia, but the phenotypic framework of fruit-panicle economic traits remains unclear. This study clarified the hierarchical structure of fruit-panicle yield formation and its relationships with panicle density and oil-related traits for breeding. All traits showed continuous variation. Panicle length, primary branch number, fruit stalk length, and fruit size were approximately normally distributed, whereas fresh panicle weight, fruit number per panicle, and secondary branch number were strongly right-skewed. Secondary branch number further showed a typical zero-inflated long-tail pattern. Single-panicle yield was directly determined by fruit number and hundred-fruit weight, while fruit number was jointly regulated by primary and secondary branching. Primary branches formed the basic panicle framework, whereas secondary branches contributed disproportionately to fruit-bearing capacity and extreme heavy-panicle phenotypes. Thus, secondary branch number is the key upstream structural target trait controlling large-panicle formation, while fruit number and hundred-fruit weight are the two major direct yield components. Panicle density is positively correlated with fruit size and branching architecture, and negatively correlated with fruit stalk length, indicating that overly compact panicles may compromise harvest performance by increasing fruit rot risk. Oil content and fatty-acid traits showed substantial variation but were only weakly correlated with most yield-related traits, indicating that high yield and high oil content can be improved simultaneously.