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Title:   Author  item
                                            Riday, Heathcliffeitem
                                            BRUMMER, CHARLES - IOWA STATE U
  Submitted to: Euphytica
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 4/20/2004
                                    Publication  Date: 7/1/2004
                                    Citation: Riday, H., Brummer, C.E. 2004. Performance of intersubspecific alfalfa hybrids in sward versus space planted plots. Euphytica. 138:107-0112.Interpretive Summary: Hybrids between purple flowered and yellow flowered alfalfa subspecies produce increased forage biomass.  This study examined if the increased hybrid forage biomass was observed in sward plots compared with space plants under a more intensive cutting management.  Increased hybrid forage biomass, although still present, was diminished in sward plots compared with space planted plots.  The diminished performance was especially noticeable in cuttings subsequent to first cutting.  This study benefits alfalfa breeders by demonstrating that proper testing of hybrid alfalfa in sward plots is necessary to obtain useful varieties to release to producers.
                                Technical Abstract: Intersubspecific hybrids between Medicago sativa subsp. sativa and subsp. falcata show biomass yield heterosis in space planted plots.  Relative biomass yield of alfalfa is known to differ in space planted versus sward plots although the magnitude of the difference is variable.  The objective of this study was to determine if and how much of the biomass yield heterosis observed in space planted alfalfa hybrids was retained in sward planted plots.  Two falcata genotypes (WISFAL-6 and PI502453-1) and three elite sativa genotypes were crossed in a diallel mating design.  Progeny were transplanted into space-planted plots and harvested three times per year or drilled into sward plots harvested four times per year.  Hybrids of WISFAL-6 with the sativa genotypes produced as much first harvest biomass yield as intra-sativa hybrids in space-planted plots and more in sward plots.  Yield in subsequent harvests was lower than intra-sativa hybrids in sward plots only.  Hybrids of PI502453-1 with sativa were generally lower yielding than intra-sativa crosses. A moderate correlation was observed between biomass yield in space planted and sward plots. Heterosis expression in swards was lower than that in spaced planted nurseries for progeny of both falcata genotypes.  The increased plant-to-plant competition in swards is the likely cause of the loss of heterosis.


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