The Effects Of Cultivation On Seed For Restoration

Abstract

Native seed for restoration is in high demand, but due to widespread habitat degradation it is unlikely that we will be able to sustainably harvest enough seed from wild populations to meet this need. In recent decades, propagation farming of native species for seed increase has emerged to address this resource gap. ¬However, few studies have tested whether this process also causes genetic degradation and loss of plant fitness which may ultimately undermine restoration success, especially under stressful conditions. To test this, we grew the eighth generation of farm-propagated Clarkia pulchella Pursh (Onagraceae) alongside seeds from the wild source populations that established the farm fields under two watering treatments. Overall, farmed seeds were 4.1% larger and had 4% greater germination compared to wild-collected seed. Additionally, farmed plants were 22% taller at flowering and had 20% larger stigmas after accounting for differences in initial seed size. Despite plants from both seed sources decreasing growth under the low-water treatment, farmed plants had 37% lower survival to the end of the experiment. Moreover, farmed plants under the high-water treatment had 80% lower fitness than wild plants due to the 1.3% greater weekly mortality and a 3-fold reduction in flowering likelihood. Together, these data suggest that bottlenecks during initial sampling and/or unintentional selection during propagation severely reduced fitness, potentially due to increased levels of inbreeding depression. To avoid degradation of seed quality during commercial propagation of native species, attention should focus on bolstering the genetic diversity of the sampled population by obtaining seed from many maternal plants from multiple large wild populations, and limiting the number of sequential generations of cultivation prior to genetic augmentation, as is supported in some seed certification programs.