Transgenic Sunflower - Genetics, Genomics and Breeding of Crop Plants - page 292

After screening, transgenic plants are established by conventional
techniques and represent the T 0 generation. A preferred technique is to
establish plantlets by in vitro grafting of regenerated sunflower shoots from
split embryonic axis explants. T 0 plants are used as pollen donors to obtain
T 1 and T 2 as successive hybrids with sunflower elite lines. The primary
transformants are typically small and stunted but T 1 plants are normal.
Transgenes are usually dominant in their inheritance and segregate in a
regular Mendelian fashion, but several copies of T-DNA are the rule (2 to
10), sometimes as incomplete, truncate segments.
9.3.3 Intended Transgenic Sunflower Releases
Since 1991, there was a continuous growth in a number of environmentally-
controlled field experiments ( Fig. 9-3 ; Cantamutto and Poverene 2007).
However, since 2000 sunflower notifications have declined , both in the US
and in Argentina, compared to corn and soybean notifications. Private seed
companies have concentrated their efforts in three agronomically important
transgenic traits: the oxalate-oxidase expressing gene for fungal disease
control, glyphosate tolerance by expressing Agrobacterium EPSPS gene cp4 ,
and the Bt toxin gene cry1 for the control of Lepidoptera ( Table 9-2 ).
Oxalic acid is a key component of infection by Sclerotinia sclerotiorum
and other fungi. The enzyme oxalate oxidase confers disease resistance
through the activation of defense genes in transgenic sunflower plants
Figure 9-3 Number of GM sunflower environmental release (bars), GM corn and GM
soybean in the US and Argentina. Sources: http: //www.isb.vt.edu/cfdocs/isblists2.cfm?opt=4
and http: //www.sagpya.mecon.gov.ar/new/0-0/programas/conabia/liberaciones_ogm.php .