Information on heritability and predicted gains from selection for increased biomass yield for ethanol production in switchgrass is limited and may vary among breeding populations. The purpose of this study was to estimate heritability and predicted gains from selection for higher biomass yield within a lowland ecotype switchgrass population, Southern Lowland 93 (SL-93), and two upland ecotype switchgrass populations, Southern Upland Northern Upland Early Maturing (SNU-EM) and Southern Upland Northern Upland Late Maturing (SNU-LM). Narrowsense heritabilities (h n 2 ) for biomass yield in each of the three populations were estimated via progeny-parent regression analysis. Half-sib (HS) progeny families from 130 randomly selected plants from the SL-93 population were evaluated for biomass yield in replicated trials in 2002 and 2003. Clonal parent plants were evaluated for biomass yield in separate environments to provide unbiased h n 2 estimates from progeny-parent regression. Yield differences were highly significant among SL-93 HS progenies within and over years. For the SL-93 population, h n 2 estimates were 0.13 and 0.12 based on individual plant and phenotypic family mean (PFM) selection, respectively. Predicted genetic gains (DG) per selection cycle were 0.15 kg dry matter (dm) plant 21 and 0.10 kg dm plant 21 for PFM and individual plant selection methods, respectively. For the SNU-EM and SNU-LM populations, year and year  HS family effects were highly significant (P < 0.01) and the HS family effect over years was nonsignificant (P < 0.05). However, HS family effects were highly significant within respective years (P < 0.01). Estimates of h n 2 for the SNU-EM and SNU-LM populations based on PFM and individual plant selection were similar, ranging from 0.44 to 0.47; DG per selection cycle ranged from 0.22 to 0.33 kg dm plant 21 .The magnitudes of the estimates of additive genetic variation suggest that selection for higher biomass yield should be possible. The substantial effect of environment on biomass yields in the upland populations and the failure of families to respond similarly over years stress the importance of adequately testing biomass yield over years.
No information is available on the effects of different biomass yield environments on selection efficiency in switchgrass (Panicum virgatum L.) breeding improvement. This study was conducted to assess the effects of high-and lowbiomass yield environments (HYE and LYE, respectively) on recurrent selection for general combining ability (RSGCA) in a lowland population of switchgrass (NL-94). The top 14 of 65 NL-94 C 0 parent plants were selected based on biomass yield of half-sib (HS) progeny tested for one post-establishment year under HYE and LYE conditions. Nine of the 14 C 0 parent plants were the same based on HS performance under HYE and LYE. Selected plants were intercrossed to produce NL-94 HYE and NL-94 LYE C 1 populations. One hundred and twenty-five HS C 1 progeny families (60 NL-94 HYE and 65 NL-94 LYE) were evaluated for biomass yield for 3 years (2002)(2003)(2004) under HYE and LYE conditions. The HYE produced about 2.5 times higher biomass yields than the LYE in both C 0 and C 1 HS progeny tests. Estimated additive genetic variance and predicted gains from selection (DG) were high in the C 1 populations indicating that RSGCA should achieve higher biomass yields. Mean biomass yields of C 1 HS families originating from the LYE protocol were significantly higher than those of families originating from the HYE protocol in both HYE and LYE performance tests, suggesting greater selection response under LYE in the C 0 population. The estimates of narrow-sense heritability ( h 2 n ) and DG from the C 1 populations indicate that positive response to selection for biomass yield is possible in subsequent cycles of selection under either HYE or LYE, with a possible small advantage for HYE.
No information is available on the efficacy of various nonparametric stability parameters when compared with GGE biplot methodology in assessing the stability of dry matter yield in bermudagrass (Cynodon dactylon L. Pers.) when a small number of genotypes is assayed. This study was conducted to compare the results of four nonparametric stability parameters developed by Huehn and Nassar (Si ), Kang's rank-sum method and the GGE biplot method for five genotypes over 11 location-year environments at Oklahoma State University experiment stations. Results from analysis of variance procedures indicated highly significant levels of genotype-by-environment interaction (P \ 0.01), which further indicated the need for stability analysis measures to be conducted. Results of the stability analysis indicated agreement among Si , Kang's rank-sum method, and the biplot method for the stability rankings of the genotypes and between these methods and the overall yield rankings of the genotypes. The S ð3Þ i and S ð6Þ i statistics were not in agreement with each other or any of the previously mentioned methods concerning the stability rankings of the genotypes. From examination of the formulae for the nonparametric statistics it was concluded that, when a small number of genotypes is assayed, the S ð1Þ i , S ð2Þ i , S ð3Þ i and Si statistics have the potential to be extremely sensitive and to produce misleading results. It was further concluded that for assessment of small numbers of genotypes the GGE biplot stability analysis method, augmented with Kang's rank-sum method, would produce the most reliable estimates of genotype stability.
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