Recurrent selection for seedling vigor in kura clover

Kura clover (Trifolium ambiguum M. Bieb.) is a rhizomatous perennial forage legume that has outstanding persistence once established. Low seedling vigor presents a challenge to kura dover establishment. Kura clover seedlings partition a significant portion of their dry matter to below ground growth. Therefore, seedling vigor could be improved by increasing dry matter allocation to the shoot. Our objective was to study the potential of recurrent phenotypic selection in the greenhouse for reduced root/shoot ratio to increase seedling vigor. Three cycles of divergent selection for root/shoot ratio and a control selection for large plant biomass (LP) were performed from a parent population consisting of 'Rhizo', ARS-2678, KZ1, and Erect Spreader populations. Selections for low root/shoot ratio (LoRS) and high root/shoot ratio (HiRS) were performed by independent culling after first selecting for large total biomass. Parent and selected populations were evaluated in the greenhouse and field. Three cycles of selection for LoRS and LP increased shoot yield in the field 42 d after planting (DAP) by 35 and 34%, respectively. Three cycles of selection for LoRS reduced root/shoot ratio in the field by 16%. Selection for HiRS did not affect seedling size in the field. Population mean shoot and total plant weights were correlated between greenhouse and field environments (average r = 0.89). Population mean seed weight was correlated with shoot weight in the field (r = 0.68, P < 0.05). The results indicate that phenotypic greenhouse selection for seedling size is an effective means of increasing seedling vigor in kura clover.