Response to Selection for Seed and Forage Traits in Smooth Bromegrass1

Abstract

Smooth bromegrass (Bromus inermis Leyss.) is an important cool‐season forage grass in the northern half of the USA and in Canada. The objective of this study was to determine the response to selection for high and low forage yield, increased seed weight, high fertility index, and greater disease resistance in a population of smooth bromegrass selected previously for increased seed weight. Six synthetics derived from fourth‐cycle selections for increased seed weight were evaluated for seed and forage traits and compared to the third‐cycle population (SBC3) from which parent clones were selected. Selection criteria for parents of each synthetic were: SB‐1, high general combining ability (GCA) for forage yield with emphasis on regrowth after early June harvest; SB‐2, high GCA for total forage yield; SB‐3, high clonal seed weight; SB‐4, high clonal fertility index; SB‐5, high GCA for resistance to brown leaf spot [Pyrenophora bromi (Died.) Drechsl.]; andS B‐6, low GCA for forage yield. Synthetics SB‐1 and 2 were similar to SB‐C3 in total forage yield. SB‐1 was 13% greater than SB‐C3 in second‐harvest forage yield. SB‐3 was 8% heavier than SB‐C3 in 100‐seed weight. SB‐4, the only synthetic satisfactory in seed yield, was 14 percentage units higher than SB‐C3 in fertility index. SB‐5 appeared more resistant to brown leaf spot than SB‐C3 and all other synthetics. SB‐6 yielded 8% less forage than SB‐C3. Significant positive correlations were obtained between Syn 2 performance of synthetics and mean topcross progeny performance of their parental clones for total and second harvest forage yield, and for brown leaf spot reaction. Relatively intense selection pressure for fertility during selection for seed weight would be necessary to maintain seed yields at satisfactory levels. Forage yield was maintained at a high level in spite of intense selection for 100‐seed weight with relatively few plants selected in each cycle.