Progress on Screening the USDA Cultivated Peanut Germplasm Collection for Variability in Seed Weight, Seed-Coat Color, Oil Content and Fatty Acid Composition.

There are over 10,000 accessions in the USDA peanut germplasm collection. Among them, 8,913 accessions are cultivated peanuts. To determine the variability of seed traits, we initiated a study to observe seed-coat color, measure seed weight, and quantify oil content and fatty acid composition by nuclear magnetic resonance (NMR) and gas chromatography (GC) for cultivated peanut accessions. To date, data have been collected from 5,527 accessions for seed-coat color, seed weight, and oil content, but only 4,100 accessions for fatty acid composition due to the longer sample preparation required for GC analysis. The seed-coat colors are classified into eight main categories: pink, red, purple, tan, white, bicolor, striped color, and mixed colors.  The 100-seed weight ranged from 21.84g to 160.20g with an average of 48.86g. The seed oil content ranged from 37.6% to 58.8% with an average of 49.2%. Peanut seeds contain eight major fatty acids - oleic (C18:1), linoleic (C18:2), palmitic (C16:0), stearic (C18:0), arachidic (20:0), behenic (C22:0), lignoceric (C24:0), and gadoleic (C20:1) and four minor acids - myristic (C14:0), palmitoleic (C16:1), linolenic (C18:3), and erucic (C22:1) acids. The average percentages of the eight major fatty acids is as follows: 11.04% (C16:0), 3.32% (C18:0), 45.31% (C18:10), 32.54% (C18:2), 1.60% (C20:0), 1.18% (C20:1), 3.40% (C22:0), and 1.62% (C24:0). The significant variability for oleic, linoleic, palmitic, and stearic acid was 30.99-80.96%, 4.24-43.33%, 5.83-15.64%, and 1.08-10.36%, respectively. Our results indicate that there is a big potential for manipulation of the levels of saturated, monounsaturated, and polyunsaturated fatty acids for improvement of peanut seed quality. Finally, additional unidentified peaks were observed in certain samples. These extra peaks may result from fatty acid degradation due to  long-term seed storage.