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Abstract
Stem explants of in vitro-propagated peach (Prunus persica L. Batsch.) cultivars Compact Redhaven, Jerseyqueen, Rio Oso Gem, and Suncrest and peach rootstock Nemaguard were infected with several strains of Agrobacterium tumefaciens. Tumor tissue was produced on all cultivars infected with strain tms328::Tn5, which carries a mutated octopine Ti plasmid pTiA6. The tumor tissues were cytokinin-independent and all tissues, except those on ‘Rio Oso Gem’, produced octopine. A DNA probe specific for the T-DNA region of the Ti plasmid hybridized to the DNA extracted from these tumors. No tumor tissue was produced in response to inoculation of the stem explants with the Ti-plasmidless strain A136 or with uninoculated controls. These results demonstrate the transformation of peach cells derived from mature plants and the potential for using A. tumefaciens to transfer economically important genes to peach.
Shoot regeneration from apple (Malus domestica Borkh.) leaf explants following particle bombardment at various acceleration pressures was studied. Basal leaf segments of micropropagated `Royal Gala' apple were bombarded with 1 μm gold particles, accelerated using helium pressures of 4.5, 6.2, 7.6, 9.3, or 13.8 MPa (650–2000 psi), and cultured on shoot regeneration medium consisting of N6 salts supplemented with 10 μM TDZ for 5, 10, or 20 days in darkness. Bombarded and control explants exhibited 63% to 100% shoot regeneration. With a 5-day dark period, average shoot production per explant ranged from 6.1 to 14; bombardments of 4.5 and 6.2 MPa significantly increased shoot production over the controls. With a 10-day dark period, average shoot production per explant ranged from 9.1 to 22 following bombardment at 9.3 and 6.2 MPa, respectively. Following bombardment at 6.2 MPa, 75% of the explants produced more than 20 regenerants per explant. With a 20-day dark period, average shoot production per explant ranged from 8.9 to 19 following bombardment at 13.8 MPa and following no bombardment, respectively. Shoot production per explant was significantly less than the controls following bombardments ranging from 6.2 to 13.8 MPa. Shoot production was highest per explant with particle bombardment at 6.2 MPa followed by incubation in darkness for 10 days. Chemical name used: thidiazuron (TDZ).
Particle bombardment has been shown to be useful for genetic manipulation of many plants; however, a critical component for successful transformation is the ability of transformed cells to regenerate plants. This study describes factors that affect the regeneration efficiency of apple leaf explants following particle bombardment. Basal leaf segments of micropropagated `Royal Gala' apple were treated with 1μm gold particles (0.5 μg/10μl), accelerated at either 4.5, 6.2, 7.6, 9.3 or 13.8 MPa, and cultured on N6 salts + l0μM TDZ regeneration medium for 5, 10 or 20 days in the dark. Both microprojectile-treated and control explants exhibited 85-100% regeneration. However, only 30-60% of the explants bombarded at 7.6, 9.3 and 13.8 MPa had more than 10 regenerants and 6-10% had more than 20 regenerants, whereas for control explants and those bombarded at 4.5 and 6.2 MPa, 70-90% had more than 10 regenerants and 30-50% had more than 20.