Additive genetic variance within populations derived by single-seed descent and pod-bulk descent

Breeders of self-pollinated legumes commonly use single-seed descent (SSD) or pod-bulk descent (PBD) to produce segregating populations of highly inbred individuals. We presented equations for the expected value of the additive genetic variance within populations derived by SSD (E(V A)SSD) and PBD (E(V A)PBD) in terms of the initial population size (N 0), the number of seed harvested per pod (M), the probability of survival of an individual (θ), and the generation at which the population is evaluated (S t). Differences between (E(V A)SSD) and (E(V A)PBD) are due to differences in the expected amount of random drift which occurs with the two methods after the S 0 generation. With both methods, random drift occurs when progeny are sampled from heterozygous parents. An additional component of random drift occurs when sampled progeny fail to survive during SSD, or when sampling occurs amoung families during PBD. For values of N 0, M, θ, and S t that are typical of soybean (Glycine max (L.) Merr.) breeding programs, (E(V A)SSD) will be greater than (E(V A)PBD). The ratio of (E(V A)SSD) to (E(V A)PBD) will: (1) increase as M and θ increase; (2) approach a value of 1.00 as N 0 increases; and (3) be a curvilinear function of S t. Plant breeders should compare SSD and PBD based upon values of (E(V A)SSD) and (E(V A)PBD) and the expected cost of carrying out the two methods.