Embryogenic callus of sweetpotato [Ipomoea batatas (L.) Lam.] disassociates in liquid medium to form a heterogeneous population of embryogenic and nonembryogenic cell aggregates of varying sizes. To improve embryo production, such cell aggregate populations were obtained by manually fragmenting calli 5 to 10 mm in size into liquid medium. The resulting suspensions were analyzed and the embryogenic fraction identified. The percentage of embryogenic aggregates and the percentage of aggregates forming embryos decreased with decreasing aggregate size. Thus, 76% of the 710- to 1000-μm-diameter aggregates but only 14% of the 180- to 250-μm aggregates had embryogenic potential. However, only 20% of the 710- to 1000-μm aggregates and only 2% of the 180- to 250-μm aggregates actually formed embryos. Conversely, embryogenic callus and embryo production per milligram of cultured embryogenic callus increased quadratically with decreasing aggregate size. Individual torpedo-stage embryos were produced from cell aggregates 180 to 250 μm in size.
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