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.
Highlights
Hybridization is common between crop and wild relatives, with 22 of the 25 most important domesticated plant species hybridizing in some part of their geographical range (Ellstrand 2003; Ellstrand et al 2013)
Field seed burial experiment: effects of removal date and cross type on seed fate In the multinomial and binomial analyses of seed fate, we found that the interaction between removal date and cross type was consistently significant (Table S1)
Subsequent analyses by removal date were performed. These analyses indicated that late-fall germination increased linearly with % crop alleles for each maternal type (Fig. 3), % crop alleles had a stronger effect on germination for F1 and crop maternal parents than for cross types produced on wild maternal plants (Fig. 3A)
Summary
Hybridization is common between crop and wild relatives, with 22 of the 25 most important domesticated plant species hybridizing in some part of their geographical range (Ellstrand 2003; Ellstrand et al 2013). Crop-wild hybridization has been shown to reduce dormancy in field studies when compared to wild seeds (Snow et al 1998; Mercer et al 2006b; Alexander et al 2014) Such field studies were carried out with a limited number of cross types and do not fully represent the genetic diversity likely present at early stages of crop-wild hybridization. We do not understand how the maternal parent of crop-wild hybrid seed may affect overwinter survival and entry into a persistent seed bank These results could imply that coexisting hybrid cross types may be more or less able to act as likely routes of crop allele introgression. To address these gaps in the literature, we studied seed dormancy, germination, and mortality patterns of a diverse array of crop-wild hybrids. Given the crucial role of seed traits and seed banks in plant populations, we expect that our results will inform understanding of the potential for crop allele introgression
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