Germplasm diversity of sunflower volatile terpenoid profiles across vegetative and reproductive organs

Cultivated sunflower (Helianthus annuus) is the fourth most important oilseed crop globally and is known to have experienced multiple genetic bottlenecks during domestication and improvement. Homogenization of crop germplasm may limit breeding efforts to improve pest and pathogen resistance or optimize other biotic interactions like pollinator attraction. Such interactions are often strongly influenced by plant phytochemistry, especially volatile compounds like terpenoids. Here we use solid-phase microextraction gas chromatography mass spectrometry (SPME GC-MS) to evaluate volatile phytochemistry across leaves, involucral bracts, disc florets, and ray floret petals in a collection of twelve inbred lines selected to represent a cross-section of sunflower germplasm diversity. Results indicate considerable compositional diversity of volatiles among lines, though substantial reduction in total volatile abundance relative to wild H. annuus. From leaves and bracts to disc florets and petals, we observe a strong increase in the proportion of monoterpenoids relative to sesquiterpenoids accompanying the transition to reproductive structures, with consistently over 85% monoterpenoids in disc florets and petals. This pattern is driven by substantially higher production of monoterpenoids (especially alpha-pinene and sabinene) in reproductive structures. Sesquiterpenoid production is roughly similar across organs, and in leaves varies among lines from 21–55% of volatiles, dominated by cadinene-type sesquiterpenoids. This work suggests that the compositional diversity of volatile terpenoids within cultivated germplasm may be sufficient for many breeding applications, though for breeding increased volatile production the use of wild H. annuus and other wild Helianthus germplasm may be necessary.