Genetic basis of autumn growth and winter hardiness in alfalfa

Abstract

Alfalfa (Medicago sativa L.) has a broad geographic distribution, with some populations adapted to cold climates and others lacking cold tolerance. Although considerable research on winter hardiness in alfalfa has been conducted, much remains unknown about the mechanisms and genetic control of winter survival. We conducted two experiments designed to identify and quantify morphological, physiological, and biochemical traits associated with winter hardiness and to estimate the genetic relationship of these traits with winter hardiness. In Experiment 1, ten alfalfa genotypes were planted in June 2000 and in May 2001 at Ames, IA, and traits were measured in August, November, and the following April in each year. Concentrations of palmitate, palmitoleate, linoleate, linolenate and total fatty acids increased in crowns and roots of all genotypes from August to November and declined by April; similar results were observed for total sugars, crude protein, and amino-N groups. Winter injury showed a negative phenotypic correlation with concentrations of palmitate, linoleate, linolenate, total fatty acids, protein, amino-N groups, and starch in both roots and crowns; no correlation was observed between winter injury and the monosaccharides glucose and fructose or soluble protein. Total and individual fatty acid concentration was not correlated with any morphological trait in autumn. These data suggest an important role of fatty acids in winter hardiness, possibly as a cryoprotective cellular mechanism. In Experiment 2, we established an F1 segregating population of 200 individuals, derived from a cross between the parental genotypes ABI408 and WISFAL-6, in the field in successive years at Ames, IA and measured the traits listed above in August and November. On average across years, the parents were similar except that ABI408 had higher shoot and viii crown biomass and stem number in August and increased concentrations of total nonstructural carbohydrates, sucrose, crude and soluble protein, and amino-N in November. WISFAL-6 had higher concentrations of starch, linoleate, and total fatty acids in November. Although differences among the individuals in the F1 population were present for all traits, and transgressive segregation present for many, the population mean tended to fall intermediate to the two parents. For root and crown mass in November, it was higher than the midparent and for crude and soluble protein in November, it was lower than the midparent. No differences in winter injury were found between the parents or between the parental midpoint and the F1 population mean. Broad sense herilabilities on an entry mean basis were 0.58 for winter injury, 0.60 for plant height in November, and ranged from 0.44 to 0.63 for shoot, crown, and root mass in August and November. Total fatty acid concentration had an H 2 of 0.72 in August and 0.44 in November. Heritabilties of most individual fatty acids, crude and soluble protein, amino-N, glucose, sucrose, total nonstructural carbohydrates, and starch were generally moderate (...

Fatty Acid Profiles of Orchardgrass, Tall Fescue, Perennial Ryegrass, and Alfalfa

“…Winter hardiness was correlated (P < 0.01) to linoleic acid in orchardgrass (r 2 = 0.08) and (P < 0.05) in tall fescue to α-linolenic acid (r 2 = 0.03) (data not shown). This result is supported by Alarcón Zúñiga (2003), who compared FA concentrations and winter injury in roots of several alfalfa cultivars diff ering in winter hardiness. Samala et al (1998) reported that the winter-hardy bermudagrass cultivar Midiron had a higher percentage of α-linolenic acid after 21 d of cold treatment than the nontolerant cultivar U3.…”

“…Therefore, it seems that an increase in the winter survivability, measured either by winter hardiness or fall dormancy has some basic impact on the FA concentrations even under nonfreezing conditions. This result is supported by Alarcón Zúñiga (2003), who compared FA concentrations and winter injury in roots of several alfalfa cultivars diff ering in winter hardiness. Cultivars with higher concentrations of linoleic, palmitic, and α-linolenic acid in autumn experienced less injury over winter.…”

“…Interestingly, tall fescue cultivar TF1 had the highest α-linolenic acid concentration and was originally selected for cold tolerance. Coeffi cients of determination for linoleic acid ranged from 0.17 to 0.50, whereas α-linolenic acid varied from 0.14 to 0.26 and palmitic acid was 0.13 (Alarcón Zúñiga, 2003). In contrast, winter hardiness in alfalfa had a much stronger correlation to individual FA when compared with that of the grass species.…”

“…However, this relationship is indicative of the amount of membrane structures contained within the chloroplasts, and not the amount of total chloroplasts. Additionally, Bolton et al (1978), using a barley (Hordeum vulgare L.) mutant lacking chlorophyll b, found that stearic and oleic acid concentrations were elevated compared with a wild-type, but that concentrations of α-linolenic and total FA were reduced. Additionally, Bolton et al (1978), using a barley (Hordeum vulgare L.) mutant lacking chlorophyll b, found that stearic and oleic acid concentrations were elevated compared with a wild-type, but that concentrations of α-linolenic and total FA were reduced.…”

Mapping Fall Dormancy and Winter Injury in Tetraploid Alfalfa

“…Environments E3 and E4 were previously described by Alarcón- Zúñiga (2003). Briefly, field plots were established using the same population at the Agronomy and Agricultural Engineering Research Farm west of Ames, IA, on 1 June 2001 and on 15 May 2002.…”