Six Virginia-type peanut (
Peanut (
Seed oxidative stability is closely associated with oil and fatty acid composition and is an important quality attribute regardless of whether it is used as food or oil. The two predominant fatty acids in peanut seed oil are oleic acid (18∶1) and linoleic acid (18∶2) which together comprise about 80% of the total fatty acid composition (
High-oleate peanut trait in a runner breeding line, F 435, was found to have 80% oleic acid and 2% linoleic acid (
Developing Virginia-type cultivars with higher levels of oleic acid and depressed levels of linoleic acid is one of several important goals in public peanut breeding programs in the US. High-oleate peanut lines were developed through backcrosses using the high-oleate line F 435 as the source of the trait and large-seeded Virginia cultivars such as NC-V 11 (
A uniform stand of healthy, vigorous seedlings is essential if growers are to achieve the yield and quality needed for profitable peanut production.
Seed quality and vigor are greatly influenced by environmental factors that occur during seed growth, development, and maturation (
In addition to influencing seed planting quality, production environment can also affect peanut seed chemical composition.
While much of the peanut industry's concern has been about peanut dietary oil quality, seed technologists know that lipids are an important source of energy for germination. Consequently, altering peanut seed fatty acid or total lipid composition could influence germination rate, seed and seedling vigor, and seedling survival, especially if seeds are planted in stressful soil conditions. Alterations of seed lipid fatty acid composition brought by traditional or molecular techniques could also change membrane lipid composition and therefore affect membrane function and permeability. Membrane integrity is linked to seed quality, seedling energy, and tolerance to environmental stress during germination and emergence. However, there is little information available in the literature on the effect of altering peanut seed lipid on seed membrane function, germination, or vigor of peanut.
With the increasing number of high-oleate peanut cultivars, there is a need to analyze quality of high-oleate peanut seed produced in various environments. The objectives of this study were to 1) determine the influence of high oleic acid on peanut seed germination and vigor; 2) evaluate planting date and harvest date affect on normal and high-oleate peanut seed germination and vigor; and 3) investigate the effect of temperature on seed oil quality of high-oleate and normal Virginia-type peanut cultivars.
High-oleic peanut lines NC 7 HO, NC 9 HO, NC 10C HO, NC-V 11 HO, NC 12C HO, and Gregory HO were developed by backcrossing the high-oleate trait from F 435 into six large-seeded Virginia-type cultivars: NC 7 (
Pedigrees of high-oleate lines developed by back-crossing the Florida high-oleic genes into large-seeded Virginia-type cultivars.
Experiments were conducted at the Peanut Belt Research Station near Lewiston-Woodville, North Carolina during 2003 and 2004 (36.07N, −77.11W). The treatment design included two planting dates, early May and early June, and two harvest dates early October and late October. A split-plot experimental design was used with 2 by 2 factorial combinations of planting and harvest date serving as whole plot treatments. The factorial combination for two peanut oleic acid levels and six cultivars were subplot. Each subplot consisted of two rows, each on a raised bed spaced on 91-cm centers and 10 m in length. Experimental test plots were established according to the treatment design of the experiment and standard production practices appropriate for the region were followed. Soil was a Goldsboro sandy loam (fine-loamy, kaolinitic, thermic typic Kandiudults) with 1.8% organic matter content and pH 6.1.
At harvest, plants were dug with a commercial digger/inverter and pods were removed by machine 3 to 4 days after digging, placed in mesh bags, and dried over non-heated forced air to approximately 8% seed moisture content. Sound mature seeds were collected from each plot, placed in plastic bags, and stored at 12 C until evaluation. Seed quality evaluation included standard germination (SG), cool germination (CG), and electrical conductivity (EC) (
Prior to SG evaluation, seeds were treated with a commercial seed treatment consisting of 45% captan, 15% PCNB, and 10% carboxin (Vitavax PC, Gustafson LLC, Plano, TX). Standard germination tests were conducted by placing four 25-seed subsamples in rolled towels at alternating 30/20 C (day/night) with 16 h at 20 C. The standard germination test procedure followed Association of Official Seed Analysts Rules for Testing Seeds (
Seeds were randomly sampled from the same seed lot used for SG and pretreated with the commercial blend of captan, PCNB, and carboxin. Cool germination tests were conducted on four 25-seed subsamples placed in rolled towels at 18 C (± 0.5 C). The test was conducted in the dark. Seedlings were evaluated at 9 days after planting and only those seedlings with radicals 2.5 cm or longer were considered to have germinated.
Seed vigor was also evaluated by electrical conductivity of seed soak water. Seeds were adjusted to about 7.5% moisture content in a chamber (Model 3020 Water Jacketed Incubator, VWR Scientific, Inc., Suwanee, GA) at 20 C and near 95% RH prior to measuring seed leakage. Fifty seed were weighed and placed in 250 ml deionized water at 25 C. Containers (Fisher Scientific Pyrex Erlenmeyer Flask, Fisher Scientific, Suwanee, GA) were covered with foil and held at 25 C (±0.5 C) for 24 h (±0.5 h). Following incubation, the containers were gently swirled and the conductivity of the seed soak water was measured using a Cole Palmer Conductivity meter model 1481-60 (Cole-Palmer Instrument Company, Niles, IL). Conductivity is reported as µohms cm−1 g−1 of seed. Two randomized subsamples from each field plot as two replications and a completely randomized design (CRD) were used in this experiment.
Prior to statistical analysis, SG and CG percentages were transformed using the angular (arcsin of square root) transformation and EC values were transformed using natural log. Analysis of variance was conducted using the general linear models procedure (PROC GLM) of SAS (SAS Institute, Inc., Cary, NC). Years and replications were considered random effects while planting and harvest dates, oleic acid level, and cultivar were considered fixed effects. Treatment means were separated by t-test using a significance level P = 0.05.
Studies were established during 2003 and 2004 in greenhouses located at the Southeastern Plant Environment Laboratory at North Carolina State University main campus. (35.77N, −78.68W) Four peanut cultivars, NC-V 11 (
The three temperature levels in this study were 22/18 C, 26/22 C, and 30/26 C day/night with 12 hours of high and low temperatures. Single plants were grown in 45-cm diameter pots filled with three parts sand (steam sterilized) and one part peat. Plants were watered twice daily with a complete nutrient solution (
Ten sound mature kernels and 15 embryos of each of the four lines produced under three environments in 2003 and 2004 were analyzed for fatty acid profile using the technique of
For statistical analysis, data were subjected to analysis of variance over two years and three temperatures based on a mixed linear model with temperature and cultivar as fixed effects of variance and year, replication (year) as random effects were used. Analyses were conducted using the general linear models procedure (PROC GLM) with random statement of SAS (SAS Institute, Inc., Cary, NC). Treatment means were separated by t-test using significance level of P = 0.05.
There was no correlation between SG and CG or between SG and EC. However, CG and EC were negatively correlated (r = −0.73, p < 0.01, data not shown). Although they measure different aspects of seed vigor, the two vigor tests appear to be in agreement when evaluating the seed lot vigor potential for the seed used in our study. It is interesting that the two outlying points are NC 10C and NC 10C HO. Why this cultivar pair does not fit into the pattern of the other five cultivar pairs is not known. Further tests might reveal any genetic influence on subsequent seed quality.
The interaction of oleic acid level by cultivar was not significant for any of the measured traits (
Mean square from pooled analysis of variance of standard germination, cool germination, and electrical conductivity.
Adjusted means of standard germination, cool germination, and electrical conductivity of six normal and high-oleic peanut lines.
When averaged across production environments, peanut seed CG was lower than SG for each cultivar used in this study (
Oleic acid level also influenced peanut seed EC (
The standard germination test is designed to provide the maximum germination percentage for the seed lot tested (
Planting and harvest date influenced SG, CG and EC but the genotype by oleic interaction was not significant (
In 2003, there was no difference in peanut SG for planting date or for harvest date (
Difference of seed quality between normal and high-oleate seed produced in varied planting and harvest dates, estimated by adjusted means of standard germination, cool germination, and electrical conductivity.
In the 2003 production environments, CG for normal cultivars was significantly higher than that of the high-oleate lines, with the exception of CG for peanuts planted on May 8 and harvested on October 7 (
Electrical conductivity was lower in normal cultivars compared to the paired high-oleate line in 2003 for all planting and harvest dates (
In 2004, there were no differences between the CG of normal and high-oleate lines for any planting date/harvest date combination (
Seed lot quality of most species is influenced by production environment. The two planting and harvesting dates for 2003 and 2004 in this experiment represented diverse production environments (data not shown). Cold and wet weather occurred between the first and second harvest dates in 2004, which resulted lower SG, CG and higher EC for seeds harvested on October 26 compared to those harvested on October 6, regardless of planting date. In contrast, 2003 weather conditions between the first and second harvests were cool with only trace amounts of rainfall. Standard germination of peanuts harvested on October 21 did not differ from seed harvested on October 7, regardless of planting date. Seed vigor of peanuts for both planting dates, as measured by CG and EC actually, increased when harvest date was delayed. However, CG and EC tests for the two years revealed that across genotype, high-oleate lines had lower vigor than normal peanut lines in each planting date and harvest date environment. Peanut growers planting high-oleic cultivars should increase the seeding density than over normal peanut cultivars.
As expected, peanut growing under the cooler temperature regime required more days to reach optimum maturity based on pod mesocarp color than warmer regimes. When pooled over runs of the experiment, approximately 175, 160, and 130 d from emergence to optimum harvest maturity were noted for the 22/18 C, 26/22 C, and 30/26 C temperature regimes, respectively (data not shown in tables).
There was no significant temperature or temperature by cultivar interaction effect on whole seed levels of palmitic acid (16∶0) (
Mean squares from analysis of variance of fatty acid and oleic/linoleic ratios for four peanut cultivars grown in three temperature environments.
Adjusted means of whole seed fatty acids of four peanut cultivars grown in three temperature environments.a
There was a significant temperature effect on stearic acid (18∶0) content (p < 0.01), but no cultivar or temperature by cultivar interaction (
Interaction of temperature by cultivar was significant for whole seed oleic acid and linoleic acid levels (
Probability associated with their F-statistic for temperature by cultivar interaction effect for oleic acid, linoleic acid, and ratio of oleic acid to linoleic acid in whole seed of each cultivar.a
Adjusted means of axis fatty acids of four peanut cultivars grown in three temperature environments.a
Temperature effects on oleic/linoleic ratio varied depending on cultivar (
Main effect of temperature and the interaction of temperature by cultivar were not significant for axis lipid fatty acid composition or O/L ratio, except for the temperature effect on palmitic acid. When averaged across the three temperature regimes for NC-V 11, NC-V 11 HO, Gregory, and Gregory HO, palmitic levels were 18.8, 12.7, 17.4, and 12.0%, respectively. The average levels of palmitic acid across the four cultivars were 13.9, 15.3, 16.6% in three temperature regimes, 22/18, 26/22, and 30/26 C. Thus, seed produced in the low growth temperature had significantly lower amounts of palmitic acid in their axis (
The high-oleate trait expressed in the oils of the whole seed (primarily storage oils) was also found in the total lipid fraction of embryonic axis. The average oleic acid content for whole seed of NC-V 11 and Gregory was 47.5 and 51.5% (
The effects of temperature on axis phospholipid fatty acids were similar to the effects on axis total lipid composition. There were no significant interactions between temperature and cultivar on any axis phospholipid fatty acid components, nor on O/L ratio. Except for stearic acid, temperature had no significant effect on axis phospholipids fatty composition or O/L ratio (
Adjusted means of axis phospholipid fatty acids of four peanut cultivars grown in three temperature environments.a
Phospholipids are primarily located in membranes, and membrane function and fluidity are greatly influenced by fatty acid composition. Membranes with high levels of unsaturated fatty acids (18∶2) are more fluid and more functional (
This research indicates that low growth temperature affected whole seed fatty acid composition, but had little or no effect on axis total or phospholipid fatty acids. Seed grown in low temperatures had decreased whole seed oleic and increased linoleic content, resulting in a decrease in the O/L ratio for seeds grown in cooler temperatures. For this research, data supports that there was significant temperature by cultivar interactions for the O/L ratio. The whole seed O/L ratio of high-oleate cultivars decreased significantly with decreasing growth temperature, but the corresponding decrease in the normal cultivars was not significant. The high oleate trait seen in the storage lipids of the whole seed was also expressed in the embryonic axis. Data indicated a significant increase in the O/L ratio of NC-V 11 HO and Gregory HO axis total lipids and axis phospholipid when compared to their normal paired cultivars. Further studies are needed to determine if the change in axis phospholipids O/L ratio seen in the high-oleate lines is responsible for any change in membrane function and peanut seed vigor.
This research was supported financially by the North Carolina Peanut Growers Association.