Effectiveness of Index Selection for Switchgrass Forage Yield and Quality
Index selection has been proposed as an effective method to improve agronomic traits in switchgrass (Panicum virgatum L.), but the actual effectiveness of this selection tool has not been determined. The objective of this research was to ascertain the efficacy of the estimated index when used to improve switchgrass forage yield and in vitro dry matter disappearance (IVDMD). Three populations were generated by selection on the basis of three different sets of criteria: (i) increased yield, with IVDMD and nitrogen concentration (N) as covariates, (ii) increased yield and IVDMD, with N as a covariate, and (iii) increased IVDMD, with yield and N as covariates. Selections were made among a total of 660 Cycle 1 plants, designating 16 plants to comprise each of the three index-derived populations. The resulting groups of plants were allowed to open-pollinate in isolation and their progeny (Cycle 2) were evaluated for forage yield and quality traits. Comparisons were made among the three groups and also with a set of 15 plants randomly chosen to represent the Cycle 0 population. Significant differences were found among the three Cycle 2 groups for yield, in vitro dry matter disappearance (IVDMD), acid detergent fiber, and neutral detergent fiber. Only the third group, selected for increased IVDMD, had regrowth IVDMD that was significantly greater than that of the Cycle 0 population. Gains in IVDMD were possible, but not without reduced gains in forage yield. Yields of Indices 1 and 2 were significantly greater than the Cycle 0 population yield for both initial growth and regrowth. Canonical discriminant analysis demonstrated the value of the three selection indices in separating the Cycle 2 population into distinct subpopulations with differing attributes. Selection indices were shown to be effective in obtaining moderate increases in trait means and in tailoring switchgrass populations with desired forage production characteristics.
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