Seed trait variation across carrots ( Daucus carota ssp. sativus ) bred for organic agriculture

Breeding crops for organic agriculture aims to address mismatches between crop trait expression and traits necessary for performance in on-farm organic conditions. Little is known about how breeding influences seed traits, which may have implications for crop performance in organic systems. We measured 11 traits related to seed size, exterior characteristics, and shape for 15 carrot varieties (Daucus carota ssp. sativus) bred for conventional and organic agriculture. Data were used to assess how seed traits vary across breeding classes (across inbred breeding lines, a first filial generation hybrid [F1] and open-pollinated [OP] varieties), and variety identity. Seed traits varied significantly among varieties, with seed sizes, exteriors and shapes being most variable across and within OP varieties. Traits related to exteriors and shape varied systematically across breeding classes. Notably, the F1 variety expressed no discernible coat or spines, while OP varieties expressed more compact seed shapes. Seed traits covaried along multivariate axes associated with (1) positive relationships among size traits, (2) a trade-off between compactness and roundness versus stylopodium length, and (3) a trade-off between seed coat width and spine length versus weight. Multivariate trait relationships varied systematically across variety identity, and to a lesser extent, breeding classes. Breeding for organic agriculture affects seed traits of crops with OP reproductive strategies, leading to more variable seed trait expression versus other breeding classes. Our results support the hypothesis that breeding for organic agriculture introduces variability in reproductive traits, which may improve crop performance under greater environmental variation commonly associated with organic systems.