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Population-Based Diallel Analyses Among Nine Historically Recognized Alfalfa Germplasms

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Population-Based Diallel Analyses Among Nine Historically Recognized Alfalfa Germplasms Theor Appl Genet (2004) 109: 1568–1575 DOI 10.1007/s00122-004-1784-8 ORIGINAL PAPER A. Segovia-Lerma . L. W. Murray . M. S. Townsend . I. M. Ray Population-based diallel analyses among nine historically recognized alfalfa germplasms Received: 11 June 2004 / Accepted: 29 July 2004 / Published online: 15 September 2004 # Springer-Verlag 2004 Abstract Identification of heterotic groups and patterns yield of M. falcata per se in the study environment and among breeding populations provides fundamental infor- consequently, low MPH values. Peruvian hybrids demon- mation to help plant breeders more knowledgeably strated the highest cross mean performance, significant manipulate heterosis. A diallel analysis was conducted positive MPH in all crosses, and positive HPH in five out among nine alfalfa (Medicago sativa L.) germplasms, of eight crosses. The results indicate that Peruvian should commonly referred to as African, Chilean, Flemish, be recognized as a heterotic group. Alfalfa breeders may Indian, Ladak, M. falcata, M. varia, Peruvian, and wish to explore opportunities for heterotic yield gains that Turkistan, which represent a significant proportion of the are likely to exist in hybrids between the Peruvian genetic diversity present in US cultivars. Heterotic germplasm and elite breeding populations, in particular, responses were determined by evaluating forage yield of those adapted to the southwestern United States. MPH the germplasms and their 36 half-diallel hybrids in seeded results suggest that alfalfa breeders may have capitalized plots that were harvested five times in each of 2 years. on the heterotic response between Flemish and M. varia Commercially acceptable yields were obtained from some during past development of alfalfa synthetics adapted to hybrids of unimproved parents, where at least one parent the central and northern latitudes of the United States. was adapted to the study environment. Variation among crosses was attributed primarily to general combining ability (GCA) effects; however, specific combining ability Introduction effects were also significant. GCA estimates for African, Chilean and Peruvian were positive, while those for Gains in alfalfa forage yield have resulted from both the Ladak, M. falcata, and M. varia were negative. Estimates accumulation of favorable alleles and through exploitation for variety heterosis effects were positive for Peruvian and of nonadditive genetic effects (Pfeiffer and Bingham 1983; M. falcata and negative for Indian and M. varia. Hill 1983; Holland and Bingham 1994; Woodfield and Significant mid-parent heterosis [(MPH) range of −21% Bingham 1995). Evidence indicates that much of the yield to 55%] and high-parent heterosis [(HPH) range of −33% gain attained since the mid-1950s likely reflects an to 23%] was detected. M. falcata hybrids exhibited the increased emphasis on intermating between multiple highest MPH values. However, this likely reflects the poor alfalfa germplasms (Holland and Bingham 1994). This breeding approach was used primarily as a means to Communicated by H. Geiger introgress more rapid regrowth into fall dormant winter- hardy populations and to incorporate resistance to multiple . * A. Segovia-Lerma I. M. Ray ( ) pests (Barnes et al. 1977). Department of Agronomy and Horticulture, New Mexico State University, Nine germplasm sources, commonly referred to as Las Cruces, NM, 88003, USA African, Chilean, Flemish, Indian, Ladak, Medicago e-mail: [email protected] falcata, M. varia, Peruvian, and Turkistan, have been Tel.: +1-505-6463819 recognized as primary contributors to contemporary North Fax: +1-505-6466041 American alfalfa cultivars (Barnes et al. 1977). Data from L. W. Murray a random sample of 90 cultivars and advanced experi- University Statistics Center, New Mexico State University, mentals registered with the North American Alfalfa Las Cruces, NM, 88003, USA Variety Review Board (http://www.naaic.org/varietyaps/ – M. S. Townsend lists/var&cultivar.html) during 1997 2002 indicate that USDA-ARS, Oregon State University, some cultivars contained varying percentages of all nine Corvallis, OR, 97331, USA germplasm sources (Table 1). In most cases, one to four 1569 germplasms (primarily two) usually predominated. The germplasm (M. sativa subsp. falcata) was represented by intermating of these germplasms decades ago undoubtedly 30 genotypes derived from a single genetically broad- resulted in linkage disequilibrium and subsequently, based accession, WISFAL (Bingham 1993). The other heterosis in many cases. However, multiple cycles of eight germplasms (M. sativa subsp. sativa and subsp. recurrent selection have since been practiced in these varia) were represented by 15 plants from each of two materials. Concern has been expressed that yield genes in “relic” seed lots that were produced on or before 1960. these genetically diverse populations may now be Relic accessions were used to increase the chance of approaching equilibrium (Barnes et al. 1977; Holland germplasm purity, because out-crossing and contamination and Bingham 1994). This could hinder yield progress by of more recently derived populations may have had a limiting future opportunities to capitalize on heterosis greater chance of occurring as alluded to by Barnes et al. through intermating of diverse gene pools for short-term (1988) and Kidwell et al. (1994). The germplasms and yield increases. Riday and Brummer (2002) reported that their representative accessions were African (Moapa and alfalfa yield improvement appears to have slowed Higazzi); Chilean (Arizona Chilean and Chilean 21-5); appreciably in some areas of the United States since the Flemish (DuPuits and Alfa); Indian (FC23631 and early to mid-1980s. FC32174); Ladak (Ladak 1 and Ladak 2); M. varia Following strategies that resulted in the tremendous (Grimm and Cossack); Peruvian (Hairy Peruvian and success of the hybrid maize industry (Melchinger and Coastal Hairy Peruvian); and Turkistan (Samarkand and Gumber 1998), it is clear that future efforts must be Tokmak). Additional information on the populations used directed towards identifying heterotic groups in alfalfa. in this study has been provided elsewhere (Segovia-Lerma Population improvement efforts must be practiced within et al. 2003). The nine germplasms were intermated by each group to maintain each population’s genetic integrity. hand (without emasculation) in a half-diallel to produce 36 Subsequent hybridization between groups will provide F1 hybrids. The F1 populations were generated by crossing breeders with the chance to exploit many forms of each plant within a germplasm to one other plant in each epistasis and to repeatedly capture heterosis (Bingham of the other eight germplasms. Parental populations were 1983). Opportunities to utilize heterosis in alfalfa as a synthesized by randomly intercrossing all genotypes means to increase forage yield has been nicely summar- within a given germplasm. An equal number of seed, ized by Brummer (1999) and demonstrated (Busbice and within each cross from each plant, was bulked to form Rawlings 1974; Riday and Brummer 2002). balanced composite populations for each inter- and Information describing population genetic parameters of intracross population. these nine key germplasms may provide insight for The 36 F1 crosses, the nine parents, and four check developing future breeding strategies to continue improv- cultivars (Dona Ana, Wilson, Commercial 1, and Com- ing alfalfa yield in North America. The present study was merical 2) were planted during March 1996, using a conducted to: (1) estimate genetic effects for these nine randomized complete block design with three replications. germplasms in order to provide retrospective insight into Each population was planted in three-row plots, 1.5 m the magnitude of additive and nonadditive effects that long, and seeded at a rate of 300 seed plot−1. Rows within have contributed to yield increases during the past plots were spaced 30 cm apart, and plots were spaced 50 years, (2) evaluate their respective diallel hybrids to 60 cm apart. Control plots of the cultivar Dona Ana were identify potential heterotic combinations that may still established between the entry plots to minimize interplot exist, and (3) document the usefulness of employing interactions. Plots were seeded on a Glendale sandy clay unimproved germplasms in alfalfa breeding programs as a loam (Typic Torrifluvent, pH 8.0) at the Leyendecker Plant means to immediately capitalize on heterosis. Science Research Center near Las Cruces, N.M., USA. Prior to planting, plots were fertilized with 122 kg ha−1 of phosphorous, and no additional fertilizer was applied to Materials and methods the plots after establishment. Plots were irrigated every 14 days from 15 April to 15 October during 1996–1998. Accessions representing each of nine alfalfa germplasm No data were collected during the 1996 establishment sources: African, Chilean, Flemish, Indian, Ladak, M. year. Plots were harvested five times, at 30-day intervals, falcata, M. varia, Peruvian, and Turkistan (Barnes et al. during May–September of 1997 and 1998, using a flail 1977), were evaluated in this study. The M. falcata harvester that cut at a 5-cm height. Forage yield data Table 1 Percentage contribution of nine germplasms to alfalfa cultivars and elite experimental lines (n=90) released in the United States during 1997–2002 Region of adaptation n African Chilean Flemish Indian Ladak M. falcata M. varia Peruvian Turkistan Unknown North Central and Northeast 48 0 5 40
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