Variation in alfalfa (Medicago sativa L.) for germination and seedling vigor at suboptimal temperatures: and laboratory and field response to selection within six alfalfa populations

Abstract

Introduction Materials and Methods 60 Results and Discussion References CHAPTER 5. GENERAL CONCLUSIONS General Discussion Recommendations for Future Research References temperatures in the laboratoiy with seed lot quality, 100-seed mass, and field emergence; (ii) to assess progress realized from phenotypic recurrent selection for germination rate and seedling growth at low temperatures under laboratory conditions in six alfalfa populations; and (iii) to asses progress in the field from phenotypic recurrent selection for cold temperature germination and seedling vigor under laboratory conditions performed in six alfalfa populations. Dissertation Organization This dissertation has been organized into four parts. The first part, this chapter, is a review of literature pertinent to the overall subject of study. The remaining chapters are organized as manuscripts to be submitted to refereed publications. Each chapter includes an abstract, introduction, materials and methods, and results and discussion section. References are listed for each part. Literature Review Origin and Adaptation of Cultivated Alfalfa Alfalfa (Adedicago sativa L.) originated near Iran, with related species located throughout central Asia and into Siberia (Barnes and Sheaffer, 1995; Hill, 1987). Cultivated alfalfa may have been in use as early at 7000 B.C, but the earliest known reference to alfalfa was from Turkey in 1300 B.C. (Hill, 1987). The use of alfalfa as animal feed was documented in the Roman Empire as early as c. 490 B.C. (Bames and Sheaffer, 1995). Alfalfa, introduced to North America in 1736, is now worldwide in distribution (Bames and Sheaffer, 1995). About 57% of U.S. production is in the north central states (esp. Wisconsin, Iowa, South Dakota, Minnesota), where it is primarily harvested and stored as hay or silage for on-farm use (Bames and Sheaffer, 1995). 3 Alfalfa is adapted to growth in cool or warm, dry climates (Hill, 1987), and is tolerant of temperature extremes (below-25 C and above 50 C) (Barnes and Sheaffer, 1995). The number of harvests per year varies from one in northem and arid regions to ten under irrigation in the southwest (Bames and SheafTer, 1995). Production is generally defined as the amount of forage dry matter (DM) per hectare (Sollenberger and Chemey, 1995). Cultivated alfalfa is naturally outcrossing (Hill, 1987). Most alfalfa cultivars are synthetic populations, produced by intercrossing individual plants selected from a breeding program (Hill, 1987). Because most recently developed synthetics are broad-based populations, formed from more than 40 parents, they can be considered highly heterogenous populations of heterozygous individuals (Bames and Sheaffer, 1995, Hill, 1987). Breeding of alfalfa cultivars in the last 25 years has focused on increases in yield, especially by increased adaptation (such as winter hardiness) and by incorporation of multiple pest resistances (Bames and Sheaffer, 1995, Hill, 1987). Some breeding effort has also been applied to improvements in forage quality, and stand establi...

Response of Six Alfalfa Populations to Selection under Laboratory Conditions for Germination and Seedling Vigor at Low Temperatures

“…Germination of alfalfa, one of the most cold resistant forage legume species, can occur at 0 to 1°C (Arakeri and Schmid, 1949; Tysdal and Pieters, 1931; Coffman, 1923), but germination rate and percentage is optimum between 15 and 25°C, as determined on the basis of an evaluation of two intermediate dormancy alfalfa cultivars (Brar et al, 1991). Variation among cultivars for germination time (GT) and root growth response has been reported across a temperature range of 5 to 30°C (Klos, 1999). Among alfalfa cultivars we have studied, some fall dormant cultivars were found to germinate more slowly at 5°C than those with less dormancy; and germination rate had a weak negative correlation with seed mass (Klos, 1999).…”

“…Variation among cultivars for germination time (GT) and root growth response has been reported across a temperature range of 5 to 30°C (Klos, 1999). Among alfalfa cultivars we have studied, some fall dormant cultivars were found to germinate more slowly at 5°C than those with less dormancy; and germination rate had a weak negative correlation with seed mass (Klos, 1999). Differences among cultivars in initial radicle growth rate at 5 to 15°C were not associated with fall dormancy rating (Klos, 1999).…”

“…Correlations of field and laboratory measurements of germination responses at cold temperatures have been examined in several leguminous crop species. In alfalfa, rapid germination and radicle growth at suboptimal temperatures in the laboratory was positively correlated with better field emergence at one of two locations evaluated (Klos, 1999). In soybean [ Glycine max (L.) Merr.]…”

Field Response to Selection in Alfalfa for Germination Rate and Seedling Vigor at Low Temperatures

“…Alfalfa seed planted under optimum conditions emerges rapidly, usually within 17 d after planting, but spring soil temperatures in this region are often suboptimal for alfalfa germination and growth (Brar et al, 1991; McElgunn, 1973; Vough et al, 1995; Weihing, 1941). At suboptimal temperatures, alfalfa cultivars differ in germination and root growth rates, and some cultivars may have better potential for good stand establishment than others (Brar et al, 1990; 1991; Klos, 1999).…”

“…Field emergence of alfalfa 8 d after planting is positively correlated with radicle growth rate and negatively correlated with germination time (GT) measured in the laboratory (Klos, 1999). Germination time was defined at the average days from planting to germination for a population of seeds (Klos, 1999).…”