Seed fates in crop–wild hybrid sunflower: crop allele and maternal effects

Abstract

Domestication has resulted in selection upon seed traits found in wild populations, yet crop-wild hybrids retain some aspects of both parental phenotypes. Seed fates of germination, dormancy, and mortality can influence the success of crop allele introgression in crop-wild hybrid zones, especially if crop alleles or crop-imparted seed coverings result in out-of-season germination. We performed a seed burial experiment using crop, wild, and diverse hybrid sunflower (Helianthus annuus) cross types to test how a cross type's maternal parent and nuclear genetic composition might affect its fate under field conditions. We observed higher maladaptive fall germination in the crop- and F1- produced seeds than wild-produced seeds and, due to an interaction with percent crop alleles, fall germination was higher for cross types with more crop-like nuclear genetics. By spring, crop-produced cross types had the highest overwintering mortality, primarily due to higher fall germination. Early spring germination was identical across maternal types, but germination continued for F1-produced seeds. In conclusion, the more wild-like the maternal parent or the less proportion of the cross type's genome contributed by the crop, the greater likelihood a seed will remain ungerminated than die. Wild-like dormancy may facilitate introgression through future recruitment from the soil seed bank.

Life history traits and phenotypic selection among sunflower crop–wild hybrids and their wild counterpart: implications for crop allele introgression

“…; Pace et al. ). Second, emergence increased for the wild‐produced cross types as percent crop alleles decreased.…”

“…; Pace et al. ). Importantly, crop–wild hybrid cross types also closely resembled wilds in average seedling emergence date and shape of emergence curves (Figs and ).…”

“…; Pace et al. ). This variation among generations from a single hybrid zone affects how introgression proceeds and will affect the phenotypes of future generations, partly through maternal and partly through nuclear genetic effects (Alexander et al.…”

“…), cross type differences may have been due to untimely fall germination, seed or seedling mortality during the winter and early spring, or continued seed dormancy; the first two might be most likely for our F 1 ‐produced cross type and the latter—for the wild‐produced cross types (Pace et al. ). Thus, germination/dormancy related traits had a large influence on the percentage of each cross type that flowered in the first year.…”

“…First, wild-produced cross types (W, BC w , and F 1 ) had higher emergence rates than the cross type produced on F 1 -maternal plants (F 2 ). This may have been due to increased fall emergence (i.e., lack of dormancy) and overwintering mortality, possibly due to more permeable seed coverings or greater sensitivity of unemerged, but germinated, seedlings of the F 2 cross type (Weiss et al 2013;Pace et al 2015). Second, emergence increased for the wildproduced cross types as percent crop alleles decreased.…”