Measurements of lethal and nonlethal inbreeding depression inform the de novo domestication of Silphium integrifolium.

Abstract

PREMISE\nInbreeding depression, or the reduction in fitness of progeny with related parents, has the potential to adversely affect the long-term viability of both wild and captive plant populations. Silphium integrifolium, a prairie plant native to the central United States, has been identified as a potential candidate for domestication as a perennial oilseed crop. Little is known about the potential for inbreeding depression in this species, but it is expected to be nonnegligible because S. integrifolium is both perennial and self-incompatible. Here, we measure lethal inbreeding depression expressed through embryo deaths, and nonlethal inbreeding depression expressed through changes in vigor and fitness phenotypes of progeny.\n\n\nMETHODS\nFirst, we made controlled crosses among related and unrelated individuals to determine the effect of two different levels of inbreeding on seed production. Then, we grew inbred and outbred progeny from this population to reproductive maturity and measured 11 key traits.\n\n\nRESULTS\nWe found that within an improved S. integrifolium population, individuals carried an average of slightly less than one lethal allele per gamete. In progeny, significant inbreeding depression was observed in at least one family for eight of the 11 measured traits.\n\n\nCONCLUSIONS\nInbreeding depression is likely to be an important challenge to S. integrifolium domestication, reducing overall population fecundity and values for important phenotypes. These effects may grow worse as selection reduces effective population size. We recommend several strategies for S. integrifolium breeding to help mitigate these problems.