Apomixis Allows the Transgenerational Fixation of Phenotypes in Hybrid Plants

The introduction of apomixis-asexual reproduction through seeds-into crop plants is considered the holy grail of agriculture, as it would provide a mechanism to maintain agriculturally important phenotypes [1, 2]. Apomicts produce clonal offspring, such that apomixis could be used to transgenerationally fix any genotype, including that of F1 hybrids, which are used in agriculture due to their superior vigor and yield [3-9]. However, traits (phenotypes) do not only result from a complex combination of genetic and environmental variation but can also be influenced by epigenetic variation, which can be transgenerationally heritable in plants [10-15]. Hence, it is far from clear whether genetic fixation by apomixis suffices to fix the agriculturally relevant phenotypes of F1 hybrids, in particular because hybridization was recently shown to induce epigenetic changes [16, 17]. Here, we show that the phenotypes of Hieracium pilosella hybrids can be fixed across generations by apomixis. Using a natural apomict, we created 11 hybrid genotypes (lines). In these and a parental line, we analyzed 20 phenotypic traits that are related to plant growth and reproduction. Of the 20 traits, 18 (90%) were stably inherited over two apomictic generations, grown at the same time in a randomized design, in 11 of the 12 lines. Although one hybrid line showed phenotypic instability, our results provide a fundamental proof of principle, demonstrating that apomixis can indeed be used in plant breeding and seed production to fix complex, quantitative phenotypes across generations.