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Raymond P. Chée and Daniel J. Cantliffe

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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Raymond P. Chée, Jonathan R. Schultheis and Daniel J. Cantliffe

Plant formation from somatic embryos in response to BAP, NAA, and sucrose was studied in sweetpotato [Ipomoea batatas (L.) Lam.]. A maximum of 15% embryos at the torpedo stage of development formed plants of agar-solidified basal medium containing 3% sucrose and no growth regulators. The percentage of embryos forming shoots was increased to 53% by 4 μm BAP, but BAP reduced whole plant formation and promoted callusing at the root axis end of embryos. The frequency of plant development was increased to 38% by adding 0.1 μm NAA to the basal medium. Reducing sucrose concentration to 1.6% in basal medium increased the frequency of plant development to 32%. Chemical names used: 6-benzylaminopurine (BAP; α-naphthaleneacetic acid (NAA).

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Raymond P. Chée, Daniel I. Leskovar and Daniel J. Cantliffe

Embryogenic callus growth of sweetpotato [Ipomoea batatas (L.) Lam.] was selectively enhanced by subculture on basal callus proliferation medium modified to contain 15 mm NH4NO3. Embryogenic callus production was doubled on basal callus proliferation medium modified to contain 60 mm K+, while nonembryogenic callus production was reduced 40%. Additions of up to 40 mm NaCl to basal callus proliferation medium did not affect callus proliferation. The development of embryos from calli subculture to embryo production basal medium was unaffected by the KCl or NaCl treatments of the callus proliferation phase. However, embryo production was increased by subculturing callus from callus proliferation medium containing 20 mm NH4 + to embryo production medium containing 10 mm NH4 + Our results demonstrate that changes in mineral nutrition, in addition to growth regulator differences between callus proliferation and embryo production media, are important factors in sweetpotato somatic embryogenesis.