effect of sheltered load on reproduction in Solanum carolinense, a species with variable self-incompatibility

• Published in: Sexual plant reproduction Vol. 22; no. 2; pp. 63 - 71
• Main Authors: Mena-Alí, Jorge I, Keser, Lidewij H, Stephenson, Andrew G
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Berlin/Heidelberg : Springer-Verlag 01.06.2009; Springer-Verlag
• Subjects: Agriculture; Alleles; Biomedical and Life Sciences; Cell Biology; evolution; fertilization; flowering plants; Flowers - genetics; Flowers - physiology; Genome, Plant; Inbreeding; inbreeding depression; Life Sciences; natural-populations; nicotiana-alata; Original Article; Plant Sciences; pollen-tube growth; Reproduction; s-alleles; solanaceae; Solanum - genetics; Solanum - physiology; Inbreeding depression; Breakdown in self-incompatibility; Sheltered load
• ISSN: 0934-0882; 1432-2145
• DOI: 10.1007/s00497-008-0092-x

In previous studies, we have investigated the strength of self-incompatibility (SI) in Solanum carolinense, a highly successful weed with a fully functional SI system that inhabits early successional and other disturbed habitats. We have found that the SI response in S. carolinense is a plastic trait--its strength being affected by the age of the flowers, and the presence of developing fruits and that there are genetic differences among families in their self-fertility. However, in species with a fully functional SI response, selfing would not be that common. As a result, deleterious recessives scattered though the genome of horsenettle are only occasionally exposed to selection. It has been suggested that deleterious recessives accumulate near S-alleles in strong SI species because the S-locus is located in a non-recombining region of the genome and because strong S-alleles are never in the homozygous state, thus sheltering some of the genetic load near the S-locus from selection. We performed a series of laboratory and greenhouse experiments to determine the extent to which sheltered load adds to the overall magnitude of inbreeding depression in horsenettle. Specifically, we amplified and sequenced the S-alleles from 16 genets collected from a large population in Pennsylvania and performed a series of controlled self-pollinations. We then grew the selfed progeny in the greenhouse; recorded various measures of growth and reproductive output; and amplified and sequenced their S-allele(s). We found that the heterozygous progeny of self-pollinations produce more flowers and have a greater ability to set both self and cross seed than S-homozygous progeny. We also found evidence of variation in the magnitude of load among S-alleles. These results suggest that sheltered load might slow the fixation of weak (partially compatible) S-alleles in this population, thus adding to the maintenance of a mixed mating system rather than leading to the fixation of the selfing alleles.