Recurrent Selection in Blue Grama. I. Seedling Water Uptake and Shoot Weight

The interval between emergence and production of adventitious roots is critical in the survival of blue grama [Bouteloua gracilis (Willd. ex Kunth) Lag. ex Griffiths] seedlings, because the threadlike seminal root and subcoleoptile internode provide the only water for the developing shoot. The objectives of this study were to evaluate plant characteristics related to water uptake and determine potential for genetic gain by selection. Six-week-old seedlings that had reached a ceiling in their capacity for 24-h water uptake were tested in a greenhouse study. Seedlings were prevented from forming adventitious roots by a dry soil layer, and pots were sealed to allow water loss only through seminal root uptake and transpiration. Shoot weights as well as water uptake values were criteria for recurrent selection of approximately the top 10% of the population over three cycles. Shoot weights of the polycross progenies from the three cycles were compared in a combined experiment. There was about a two-fold difference (P < 0.01) in water uptake and shoot weight between the lowest and highest progeny in each generation, with broad-sense heritabilities of 62 and 69% on a family mean basis indicating useful genetic variance in those traits. Results indicated a 21% increase in shoot weight for two cycles of simple recurrent selection, and narrowsense heritability by parent-progeny regression was 48% and 42% for the second and third cycles. Shoot weight was significantly (P ≤ 0.01) associated with water uptake (r = 0.81) and with caryopsis weight (r = 0.40). Selection for high shoot weight in seedlings (from high caryopsis weight parents) supported by the seminal root, rather than selection for water uptake, should result in more efficient progress because a larger number of seedlings could be evaluated. Genetic gain with use of this approach should increase survival and establishment of blue grama seedlings.