Evidence That 2n Eggs Explain Partial Hybrids between and .

Selected genotypes of alfalfa () produce partial hybrids in sexual crosses with , as reported in (2013). The hybrids contain mostly alfalfa DNA and traits, but also contain DNA and traits from . It was proposed in 2008 that the partial hybrids could be explained by fertilization of 2n eggs in alfalfa by normal pollen from , followed by partial loss of chromosomes during embryogenesis. In this paper, we confirm the presence of 2n eggs in the first alfalfa parents that produced hybrids. The test for 2n eggs involved pollinating 4x alfalfa with pollen from 8x alfalfa. The production of 8x progeny in the cross proved that selected alfalfa parents produced 2n eggs. Thus, 2n eggs appear to explain how the partial hybrids (hereafter hybrids) contain mostly alfalfa DNA and traits. However, two of the six alfalfa plants that did not hybridize with also had 2n eggs. Thus, although 2n eggs explain the alfalfa content of hybrids, 2n eggs are not the only factor involved in weakening the hybridization barrier, and in transferring genes to alfalfa from .