The in vitro shoot proliferation ofPopulus alba XP. grandidentata was affected by the medium consistency and shoot density, but not by three sizes of vessels. After 4 weeks of culture, the fresh weight and number of shoots per explant on liquid medium were significantly greater than those on agar-solidified medium. In particular, 3.2 shoots, 7 mm or longer per explant, were produced on liquid medium compared with 1.6 shoots per explant or agar-solidified medium. The fresh weight per exp'lant after 4 weeks of culture on liquid medium and agar-solidified medium were 0.68 and 0.25 g, respectively. Increasing the number of shoots per vessel slowed the growth of the explants as measured by fresh weight and the number of shoots produced. There was little difference in the number of shoots produced between vessels with 1 or 2 shoots per vessel, but there were many fewer shoots produced when 3 shoots were placed in each vessel.

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Leaf pieces of in vitro-cultured plantlets of the wild potato species Solanum brevidens Phil. were cocultivated with Agrobacterium tumefaciens that contained nptII and uidA genes on the disarmed plasmid pBI121. Independent transgenic shoots were regenerated from solidified and liquid medium that contained 50 mg l(-1) kanamycin. Two Agrobacterium strains were investigated for transformation efficiency. GV2260, which contained p35SGUSINT, resulted in a 11% transformation frequency, compared with 1% using LBA4404. Transformation rates were 7% in liquid culture and 3% on solidified medium. All kanamycinresistant, putatively transformed plantlets were confirmed positive by histochemical GUS assays. GUS activity in 22 independently transformed plants was quantified by fluorometric assay. Southern analysis of randomly selected transgenic plants showed that each transgenic plant contained at least one copy of the uidA gene.

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Certain parent-progeny crosses were studied to determine whether several S loci acted independently or epistatically to produce incompatibility in garden chrysanthemums, Chrysanthemum morifolium RAMAT . The ratios of compatible : incompatible crosses with the original parent, as the pollen parent, were nearly 1 :3, 1 :1, and 1 :1 for the I,, backcross (BC), and BCF2 generations, respectively . In particular, crosses between each progeny and the original parent showed that the number of compatible crosses was much higher than expected if each S locus acted independently . Therefore, interaction must have existed among pollen S alleles from different S loci . This information was used to demonstrate a method by which garden chrysanthemums could be inbred by sib mating in successive generations .