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and the bar gene was transmitted through both male and female gametes and expressed in T 1 progeny. Although Agrobacterium tumefaciens has been successfully usedMicroprojectile bombardment and gene transfer by to transfer genes to a wide range of plant species, it has received lit-A. tumefaciens are currently the two most common tle attention for transformation of forage grasses. Therefore, the obmethods for achieving genetic transformation in higher jective of the present study was to demonstrate Agrobacterium-mediated transformation of switchgrass (Panicum virgatum L.). The plants. Although not universally accepted (Smith et al., A. tumefaciens strain AGL 1 carrying the binary vector pDM805, 2001), it has been reported that Agrobacterium-mediated coding for the phosphinothricin acetyltransferase (bar) and ␤-gluctransformation leads to clean, discrete, low copy, welluronidase (gus) genes, was utilized in these experiments. Somatic emdefined, unrearranged DNA insertions into the plant bryos, embryogenic calluses, mature caryopses, and plantlet segments genome (Chilton, 1993; Repellin et al., 2001; Upadhyaya served as target tissues for infection. Treated cultures were selected et al., 2000). There are now several publications describin the presence of 10 mg L Ϫ1 bialaphos and the resultant plantlets ing genetic transformation in various cereal species uswere treated with the herbicide Basta [monoammonium 2-aminoing Agrobacterium (Repellin et al., 2001). The only pre-4(hydroxymethylphosphinyl)butanoate]. T-DNA delivery efficiency vious report of gene transfer in a forage or turf grass by was affected by genotype, explant used and the presence or absence this method was for GFP in creeping bentgrass {Agrostis of acetosyringone (3,5-dimethoxy-4-hydroxyacetophenone) during inoculation and cocultivation. Approximately 600 transgenic plants palustris Huds. [ϭ A. stolonifera var. palustris (Huds.) were produced, and transformation efficiencies ranged from 0 to Farw.]; Yu et al., 2000}. nearly 100%. Stable integration, expression, and inheritance of bothThe objectives of the present study were to demontransgenes were confirmed by molecular and genetic analyses. Apstrate high efficiency Agrobacterium-mediated transforproximately 90% of the tested plants appeared to have only one or mation in switchgrass, and to show sexual transmission two copies of the T-DNA inserts. Controlled crosses between T 0 of the transgenes and their expression in T 1 progeny. and nontransgenic 'Alamo' plants indicated the expected ratio of 1:1The accomplishment of such provides an alternative to (transgenic:nontransgenic) in T 1 plants for both transgenes according microprojectile bombardment for genetic manipulation to a 2 test at P ϭ 0.05. These results indicate that the Agrobacterium of this species. method is effective for transferring foreign genes into switchgrass.

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Segments taken from the basal 15 to 20 millimeters of the two innermost leaves of an orchardgrass (Dactylis glomerata L.) genotype produced somatic (nonzygotic) embryos directly from mesophyll cells without an intervening callus when cultured on an agar medium with 30 micromolar 3,6-dichloro-o-anisic acid (dicamba). This demonstration of high-frequency embryogenesis from mesophyll cells in Gramineae is strong evidence for totipotency of the cells.

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