Evidence for Outcrossing in the Perennial Forage Legume Tedera

Tedera [Bituminaria bituminosa (L.) C.H. Stirt. vars. albomarginata and crassiuscula] is a traditional perennial forage legume of the Canary Islands (Spain). There is growing interest in expanding its cultivation into other Mediterranean-type climates due to its high-quality feed characteristics and its excellent productivity in dry conditions. Plant breeding programs have been established in mainland Spain and Australia, which are tasked with developing well-adapted and productive cultivars for these new environments. Being a new arrival to modern plant breeding, there are many gaps in our basic understanding of tedera including its mode of reproduction. Previous research suggested that tedera is mainly self-pollinating with some degree of outcrossing. The purpose of this experiment was to confirm that outcrossing occurs in tedera in normal field conditions. Six elite parents were clonally propagated and single clones of each parent were allowed to open-pollinate at three field sites and in a phytotron control. Four microsatellite markers were used to determine unambiguously the provenance of 362 seeds sampled evenly from parental clones grown in four environments. We found that most tedera elite parents outcrossed at moderate frequencies (up to 40%; average 7.8%) at two out of the three field sites, including between botanical varieties. These findings have clear implications for the new tedera breeding programs where outcrossing levels are sufficiently high to require plant bagging or plot isolation to prevent unintended cross-pollination between breeding lines. Conversely, outcrossing levels are likely to be too low for the development of synthetic varieties.