Clonal populations regenerated from single-leaf cell protoplasts of the potato cultivar ;Russet Burbank' display a high frequency of variation for several horticultural and disease resistance characters. Observations over a period of three tuber generations suggest stable changes in tuber shape, yield, and maturity date, in photo-period requirements for flowering, and in plant morphology. Enhanced resistance to early blight (Alternaria solani) and late blight (Phytophthora infestans) diseases also regularly occurs within regenerated populations. These findings are discussed in the context of possible application to varietal improvement, particularly as they pertain to asexually propagated plants.

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Transgenic cucumber plants (Cucumis sativus L., cv. 'Straight Eight') were regenerated from roots induced by inoculation of inverted hypocotyl sections with Agrobacterium rhizogenes containing the vector pARC8 in addition to the resident Ri-plasmid. The DNA transferred to the plant from the vector (T-DNA) included a gene which encoded the enzyme neomycin phosphotransferase II, and thus conferred on the plant cells resistance to kanamycin. The transgenic plants looked normal and were positive for the neomycin phosphotransferase II. Southern blot analysis of the transgenic plants revealed that all plants contained vector DNA, but only some of them contained DNA from the Ri plasmid.

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Tomato plants resistant to the fungal pathogen, Fusarium oxysporum f. sp. lycopersici, race 2, were obtained using in vitro selection against fusaric acid, a non-specific toxin, as well as non-challenged cells. Protoplasts were isolated from cotyledonary tissue of tomato cv. 'UC-82', which is susceptible to Fusarium race 2. Protoplasts were challenged with the toxin, and the resistant calli were further subjected to the toxin. Plants regenerated from toxin-resistant calli were screened for resistance to the pathogen by using the Fusarium slurry inoculation technique. Seeds were collected from the surviving individuals, germinated and rescreened for resistance to the pathogen. Data obtained from this test showed a ratio of three resistant to one susceptible among R1 progenies. Further analysis of the R2 progenies confirmed that the fusarium-resistant plants were either homozygous or heterozygous dominant for the gene conferring the resistance. Similar results were recorded for tomato plants regenerated from cells that received no selection pressure. The nature of this single dominant gene-type of resistance is under investigation.