Alfalfa Genotypes Research Articles

Observations on the rapid size-exclusion chromatography of proteins

The retention behaviour of reference proteins on commercial siliceous size-exclusion supports was studied. Sorption was observed on both surface modified and unmodified supports. When sodium dodecylsulfate was added to the aqueous mobile phase, normal elution patterns were found. With this system, proteins, such as those isolate from different alfalfa genotypes, may be compared rapidly. Comparisons were facillitated by use of on-line central data processing capability.

Interacting effects of subsoil acidity and water on the root behaviour and shoot growth of some genotypes of lucerne (Medicago sativa L.)

The effects of additions of calcium carbonate to a low-calcium, acidic subsoil, underlying a fertilized, limed surface soil, on the root and shoot growth of four lucerne genotypes were studied in deep (85 cm) soil columns. Separate surface and subsoil watering treatments were included after plants were established. A comparison showed that, at low rates of addition, calcium carbonate was more effective than magnesium carbonate in promoting root elongation, but more generally the increase in pH appeared to be the important factor. Surface droughting reduced shoot growth, but the response to subsoil lime continued as long as subsoil moisture was supplied, in accordance with the increased root penetration and ability for water uptake. Thus shoot growth under surface drought reflected (r = 0.973) the total length of deep roots (> 60 cm depth) over all genotypes and lime treatments. The genotypes, which included three from cv. Hunter River and one from cv. Siro Peruvian, differed in several respects. Our selections from Hunter River varied in root morphology, shoot:root ratios and type of response to subsoil lime. The Siro Peruvian genotype produced abundant deep, fine roots and good shoot growth under surface drought.

Variation Among Alfalfa Genotypes for Rate of Acetylene Reduction1

Alfalfa (Medicago sativa L) cultivars with increased symbiotic N fixation potential would be useful in many agricultural systems for supplying N for grain and pasture crop production. This paper describes a greenhouse procedure for evaluating alfalfa for rates of acetylene reduction and characterizes genetic variation of traits that may influence nitrogen fixation in alfalfa. Two thousand plants of six alfalfa cultivars were scored for nodulation when inoculated with a mixture of Rhizobium meliloti strains. Seventy‐seven plants, representing extremes in nodulation, were selected and vegetatively propagated (cloned). Clones differed significantly for nodulation, root type, and acetylene reduction in replicated tests. Crosses were made in all possible combinations among six clones differing in acetylene reduction potential. Progenies were established in sand benches, allowed to grow to flowering, and then cut off. When the regrowth was at the early bud stage, plants were assayed for acetylene reduction and evaluated for nodulation and root morphology. Crosses between clones with high acetylene reduction values produced progenies with acetylene reduction rates more than twice those of progenies from low ✕ low crosses. Crosses between clones with high acetylene reduction values and clones with low acetylene reduction values produced progenies with intermediate values. Morphological traits associated with high levels of acetylene reduction were: many fibrous roots, many nodules, and high top and root weights. These greenhouse results indicated that significant variation exists among alfalfa genotypes for factors that may be associated with N fixation.

Effects of temperature on the photosynthesis–irradiance response curves of newly matured leaves of alfalfa

Various carbon dioxide exchange characteristics are described for two alfalfa (Medicago sativa L.) genotypes (AT 171 and CC 120) grown at 20:15 °C and 30:25 °C day:night temperatures and 53 nE cm−2 s−1 irradiance (400–700 nm). Growth at 30:25 °C as compared with 20:15 °C resulted in lower net carbon dioxide exchange rates (NCE) for both genotypes when analyzed at 20 °C, but did not cause any sizeable change for CC 120 at 30 °C. Oxygen inhibition of photosynthesis increased with irradiance to 48 nE cm−2 s−1 but either declined or remained constant with further increase in irradiance. Oxygen inhibition was higher at 30 °C than at 20 °C and was not consistently influenced by growth temperature. However, the ratio of oxygen inhibition to carbon dioxide exchange rate in air containing 1% oxygen and the mesophyll resistance were greater with AT 171 grown at 30:25 °C than at 20:15 °C, particularly at high irradiances. NCE measured at 20 °C instead of 30 °C for plants grown at 30:25 °C was reduced to a much more marked extent with CC 120 than with AT 171; this difference was paralleled by a more marked increase in stomatal resistance length (rSL) for CC 120.rSL decreased with an increase in irradiance, was generally higher at 20 °C than at 30 °C, and did not differ between growth temperatures when measured at an irradiance of 116 nE cm−2 s−1 and a temperature equal to the day temperature of the growth regime. The results are discussed in relation to factors responsible for adaptability to different thermal environments.

Effects of subsoil calcium on the root growth of some lucerne genotypes (Medicago sativa L.) in acidic soil profiles

The root growth of lucerne was examined in an acidic soil profile modified by varying additions of calcium carbonate to different layers of the subsoil. Root growth responded strongly to changes in the concentration of exchangeable soil calcium. Symptoms of thickening, distortion and poor lateral formation occurred under low calcium treatments. The results were in agreement with the interacting effects of calcium (at 0.5–5.0mM) and aluminium ions (at 0–20,µM) on lucerne in separate solution culture experiments. Differences in root penetration were observed between three lucerne clones selected from the cultivars Hunter River and Siro Peruvian. At the first harvest, the magnitude of these differences was increased by the addition of lime to the profiles. The three genotypes produced similar total dry weight yields, but differed in their distribution of growth between shoots and roots. This distribution was not affected by the addition of lime to the subsoil. However, the length of roots in the lower layer of the profile ( > 60 cm depth) was more responsive to subsoil treatment than was total dry weight. At the final harvest, the shoot yields of two genotypes were affected by lime treatments, but that of the deepest-rooted genotype was not. The results suggest that improved genotypes could be selected from Australian lucernes for establishment in areas with acidic subsoils, but that selection on root penetration alone would not necessarily lead to increased shoot yields.

WATER USE OF ALFALFA GENOTYPES OF DIVERSE GENETIC ORIGIN AT THREE SOIL TEMPERATURES

The efficiency of water use of 15 alfalfa genotypes of diverse genetic origin was studied in a growth room at three soil temperatures. The genotypes were similar in water used per unit of dry matter produced, but there was a significant temperature × genotype interaction. Genotypes of Medicago falcata L. used less water per day than genotypes of Medicago media Pers. and Medicago sativa L., but this was due to their slower growth rate. It was concluded that to develop higher yielding cultivars for optimum moisture conditions, selection should be for high rate of growth and rapid recovery and not for water use efficiency.

Relationship of Mitochondrial Efficiency to Forage Yield in Alfalfa1

The utilization of a physiological variable to determine yield potential could serve as a valuable tool for plant breeders. The object of this study was to determine if a relationship existed in ratios of adenosine diphosphate (ADP) to oxygen (mitochondrial efficiency) and forage production in alfalfa (Medicago sativa L.).Significant differences in ADP:O among mitochondria isolated from 5‐day‐old seedlings of several lines of alfalfa were found. When ADP:O means of the seedlings were compared to forage yields obtained from field studies, significant positive correlation coefficients were found. Correlations were highest during cooler portions of the growing season (spring, fall) when yields are normally highest and lower during the summer months when forage production/harvest is low.It would appear that the laboratory determination of ADP:O ratios may have potential as a physiological tool for the selection of high yielding alfalfa genotypes when grown under optimum conditions. When factors such as physical environment, insects, or diseases are the yieldlimiting variables the relationship may not be as valid.

Effects of temperature on the morphology and photosynthetic activity of newly matured leaves of alfalfa

Effects of temperature on (1) physical characteristics of newly matured leaves throughout regrowth, and (2) net carbon dioxide exchange–irradiance response curves throughout regrowth and throughout the day are described for two alfalfa (Medicago saliva L.) genotypes (AT171 and CC120) grown at 20/15C and 30/25C day/night temperatures and 53 nE cm−2 s−1 irradiance (400–700 nm).Area per leaf increased linearly with increasing leaf number up to the fourth or fifth leaf, and thereafter remained constant. Both specific leaf weight and leaf density were constant for the first four leaves, and increased sharply thereafter, particularly at day/night temperatures of 20/15C. Percentage of leaf water content did not change throughout regrowth at 30/25C, but decreased after leaf 4 at 20/15C. Intercellular space volume fluctuated with leaf number. Leaf area was larger, specific leaf weight, and leaf density were greater, intercellular space volume was higher, and percentage of leaf water content was lower, with plants grown at 20/15C than at 30/25C.The net carbon dioxide exchange rate at 116 nE cm−2 s−1 increased with leaves produced progressively until a peak was reached at leaf 4 or 5 and then decreased. At any given leaf position, net carbon dioxide exchange rate at 116 nE cm−2 s−1 was greater at 20/15C than at 30/25C for AT171, but was the same at both temperatures for CC120. In contrast, net carbon dioxide exchange rate at 76 nE cm−2 s−1 was greater at 20/15C than 30/25C for both genotypes. Net carbon dioxide exchange rates measured in the morning were always lower than those measured in the afternoon regardless of irradiance, genotype, and growth temperature.

The effect of lime and two strains of Rhizobium on ten genetically distinct lines of lucerne

In a pot trial of ten lucerne lines, there were differences among lines in yield only with 502 kg ha-1 of added calcium carbonate, and not at higher or lower levels. Genetic variation for yield was expressed only ,in this sub-optimum environment, and selection for increased response appears possible. A common acid-producing strain of Rhizobium was more effective for most lucerne genotypes than an alkali-producing strain over a range of soil pH.

THE BEHAVIOR OF SOME ROMANIAN ALFALFA GENOTYPES TO SALT AND HYDRIC STRESS

Abiotic stress conditions cause extensive losses to agricultural production worl dwide (Bray, 2002). Drought and salinity stress can significantly affect plant yield in arid and semi-arid regions and not only. Climatic changes will conduct to severe drought conditions and to aridity of some important regions in Romania. One of the most important strategies which could reduce the influence of drought and salinity on alfalfa (Medicago sativa) production is to breed for increased cultivar tolerance. The present paper reports the reactions of some Romanian alfalfa genotypes to salt and water stress. The aim was to elucidate some physiological and metabolic aspects of those stresses, in order to establish screening criteria to facil itate the development of genotypes with enhanced tolerance to field stress conditions. Seeds of nine alfalfa genotypes were sown in Mitcherlich plots filled with a soilsand mixture. The plant were grown in vegetation house under optimal condition up to just before flowering, when for water stress variant the watering was reduced for 10 days; salt stress was imposed on plants by adding 300 mM NaCl/l and under combined stress the plants were treated with 300 mM NaCl/l one week before reducing watering. The alfalfa yield of all studied genotypes was significantly reduced under water and salt stress while stresses combination caused a reduction on fresh biomass, too. Salt stress significantly decreased biomass by more than 37% while water stress by more than 73%. The effects of salt and water stresses on yields were additive but not equal. Alfalfa responded to drought by decreasing leaves transpiration. Between bi omass accumulation and leaves transpiration under water and salt stress there was a linear relationship (r = 0.76*; r = 0.82*). Under optimal condition the proline content was very small (1.7-5.4 mg proline/g f.w.) but there were obviously higher proline contents under salt stress (156-441 μM proline/g f.w.), water stress (45-68 μM proline/g f.w.) and stress combination (120-330 μM proline/g f.w.). The negative effect of salinity and combined stresses on alfalfa growth could be attributed to osmotic effects. Osmotic stress inhibits water uptake from the soil and requires the plant to use energy and carbohydrates in synthesizing organic solutes to adjust its internal osmotic potential. Yield loss results from closing stomata and from energy and carbohydrates use in osmoregulation. The leaves transpiration and biomass accumulation were correlated, suggesting the use of transpiration as a screening tool for drought and saline tolerance of alfalfa genotypes.