Many of the accessions in the Pisum Core Collection are mixtures of diverse germplasm. Because we were interested in characterizing seed and pod wall parameters in unique lines, we randomly selected seeds of a single seed phenotype within each accession for planting. For the most part, this resulted in plants with uniform characteristics, within each planted accession. At harvest, if more than one plant phenotype was evident, we selected seeds from only one plant phenotype (usually the phenotype with t he most plants, or the highest seed yield). We also ensured that its seeds were of the same phenotype as the original seeds planted. Phenotypic data were collected on harvested seeds and pods of each accession, and these characteristics are noted in the dataset.
Six plants of each accession were grown in 5L black plastic pots filled with a synthetic soil mix composed of 2 parts Metro-Mix 360 (Scotts-Sierra Horticultural Products Co., Marysville, Ohio) and 1 part vermiculite (Strong-Lite Medium Vermiculite, Sun Gr o Horticulture Co, Seneca Illinois). Plants were grown in a controlled environment greenhouse with a temperature regime of 22 ( 3 oC/day and 20 ( 3 oC/ night, with a relative humidity ranging from 45% to 65% throughout the day/night cycle. Sunlight was supplemented with metal halide lamps, set to a 15-h day, 9-h night cycle (lights on at 700 h). In order to maintain an adequate supply of all mineral nutrients, a complete fertilizer mixture was provided to each pot on a daily basis. Pots were irrigated with an automated drip irrigation system (one drip line to each pot); the system was regulated with a timer that delivered nutrient solution twice a day (younger plants) or three times a day (older plants) in sufficient quantity to saturate the soil mass at each irrigation. The nutrient solution contained the following concentrations of mineral salts: 1.0 mM KNO3, 0.4 mM Ca(NO3)2, 0.1 mM MgSO4, 0.15 mM KH2PO4 and 25 uM CaCl2, 25 uM H3BO3, 2 um MnSO4, 2 uM ZnSO4, 0.5 uM CuSO4, 0.5 uM H2MoO4, 0.1 uM NiSO 4, 1 uM Fe(?)-N, N'-ethylenebis[2-(2-hydroxyphenyl)-glycine] (Sprint 138; Becker-Underwood, Inc., Ames, Iowa, USA). We thus attempted to maintain all essential minerals at sufficient, non-toxic levels in the soil.
All pods were harvested at full maturity. Five pods of each accession were randomly selected, with pods coming from five different plants within that accession. An attempt was made to select those pods in which all or most of the potential seed position s within a pod were filled with a developing seed (i.e., low rates of abortion). These five pods were used for the seed partitioning calculation; all other pods for the accession were collected and bulked together, with seeds being removed from the pods at harvest. The five pods and the bulked seeds were then dried in an oven at 70C until constant dry weights were attained. After drying, each of the five pods was carefully opened, and counts were made of fully developed seeds, as well as total number o f seed positions within each pod (i.e., aborted plus non-aborted seeds). Dry weights were determined for the combined pod wall halves (minus pedicel and floral tissue), and the seeds, for each pod. The bulked seeds were counted and their combined dry we ight was determined. Observations were additionally made on the pod walls, to note the presence or absence of neoplastic growth on the pod wall surface.
The 100 Seed DW was determined as a mean value for each accession based on the combined dry weight and number of seeds from the bulked harvest and the five additional pods. The Seed Positions per Pod descriptor was determined as a mean value for the five pods. For the Seed DW Partitioning descriptor, an average seed mass (DW/seed) and an average pod wall DW/seed (using the total number of aborted and non-aborted seed positions in the denominator) were calculated for each pod. The Seed DW Partitioning v alue for each pod was calculated as a percentage according to the following equation: Seed DW Partitioning = [(average seed mass) * 100/((average seed mass) + (average pod wall DW/seed))]. The five pod values were used to determine a mean for each accession. Variability amongst the 5 pods was <6%, and averaged 2.1 % across all accessions.