Bioprospecting for improved floral fragrance in wild sunflowers

Cultivated sunflower (Helianthus annuus) is not typically considered to
have a pleasant floral fragrance. In field production, seed yield is often
limited by pollination services, particularly in the production of hybrid
seed. Improved floral fragrance, as determined by volatile organic
compounds, maybe a route to improving pollinator attraction for oilseed
and confectionary production and could also add value to ornamental
sunflowers. Wild relatives of H. annuus have a long history of being used
to breed improved traits into cultivated varieties, yet it is unknown
whether favorable scents are present in wild Helianthus species and thus
an available resource for fragrance breeding. To assess the diversity of
floral fragrance available in crop wild relatives, 30 diverse accessions
of wild Helianthus as well as seven varieties of H. annuus spanning a
domestication gradient were grown in greenhouse experiments and variation
in floral volatiles was analyzed by solid phase microextraction-gas
chromatography-mass spectrometry. While alpha-pinene made up a significant
portion of the volatiles emitted for most taxa, there was substantial
diversity present across the genus as well as within H. annuus. Most
volatiles emitted were monoterpenoids with a significant share of
sesquiterpenoids. The diversity identified here will inform further
targeted study of which compounds affect pollinator attraction and health.
Several wild accessions such as H. debilis subsp. tardiflorus and H.
praecox subsp. praecox as well as open-pollinated domesticated accessions
of H. annuus show promise for breeding for improved floral fragrance due
to high volatile abundance and likely favorable compound compositions.