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Title:   Author  item
                                            Riday, Heathcliffeitem
                                            BRUMMER, CHARLES - IOWA STATE U
  Submitted to: Crop Science
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 9/5/2003
                                    Publication  Date: 1/1/2005
                                    Citation: Riday, H., Brummer, C.E. 2005. Heterosis in a broad range of alfalfa germplasm. Crop Science. 45:8-17.Interpretive Summary: Hybrid varieties between yellow and purple flowered alfalfa increased yield compared to traditional alfalfa varieties.  This study examined yellow by purple flowered alfalfa hybrids and found that eastern European yellow flowered alfalfas were the highest yielding hybrids in combinations with purple flowered commercial alfalfa.  Based on this study focused selection of yellow flowered alfalfa plants and plant sources can be made.  Such selection will benefit alfalfa growers through the creation of high yielding hybrid alfalfa varieties.
                                Technical Abstract: Crosses between Medicago sativa subsp. sativa and subsp. falcata produce progeny exhibiting heterosis for biomass yield.  The purpose of this study was to determine which subsp. falcata germplasm produced the best hybrids in testcrosses with elite subsp. sativa material in order to guide future breeding efforts.  Over 100 falcata genotypes from 40 populations were test crossed to four elite sativa populations.  Testcross progeny and parental clones were grown for two years in two locations and harvested three times per year to determine biomass yield.  A broad range of testcross performance was observed, with mean heterosis values approximately zero.  The highest yielding sativa-falcata hybrids were derived from European falcata germplasm.  North American semi-improved falcata germplasm performed well in hybrid testcrosses.  Pre-selection of parental falcata genotypes for autumn growth was associated with higher yielding testcross progeny.  Positive heterosis was seen during the first harvest, but negative heterosis was often observed during second and, to a smaller extent, third harvests.  Superior sativa-falcata hybrids were observed that showed good biomass yield and heterosis during all three harvests.  Parental yield was least predictive of hybrid progeny yield during first harvest (h2 = 0.12).  Heritability increased during second and third harvest to 0.31 and 0.33, respectively.  Expected genetic gain per selection cycle is greater using progeny testing compared to simple recurrent phenotypic selection.


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