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caused by Sclerotinia through overexpression of the oxalate oxidase (OXO)
enzyme, which degrades oxalic acid to carbon dioxide and hydrogen
peroxide as a hypersensitivity mechanism. The first strategy outlined for
sunflower by Lu et al. (1998) was also successful in other host plants.
Donaldson et al. (2001) demonstrated that wheat gene expression of the
OXO enzyme in soybean cell walls close to the site of pathogen attacks
reduced disease progression.
The OXO effect in sunflower seems to be more than a hypersensitivity
mechanism. Hu et al. (2003) demonstrated that fungus-related damage
promotes defense gene activation that is independent of cell death in GM
plants that express the wheat OXO gene. The transgenic event TF28
significantly improves white mold resistance in cultivated sunflower (see
supporting online material in Burke and Rieseberg 2003). The OXO
expression may also reduce the herbivory action of certain insects, as
demonstrated in maize under field conditions (Ramputh et al. 2002).
Other diseases that have attracted attention in recent research include
more sunflower-specific pathogens, among them downy mildew caused by
Plasmopara halstedii , an oomycete native to America but has spread all over
the world. It is an obligate biotrophic plant pathogen that can be controlled
through the development of elite sunflower lines resistant to its different
races using molecular marker-assisted selection (Pankovic ' et al. 2004).
Genetic resistance mechanisms are linked to the lack of expression of
pathogenesis-related proteins in resistant lines (Roldan Serrano et al. 2007).
PlArg from Helianthus argophyllus provides a new source of resistance against
P. halstedii in sunflower (Dussle et al. 2004). Cultural control methods,
including seed treatment with fungicide (i.e., metalaxil), are generally
recommended for downy mildew control, and on the same accounts for
other two significant diseases, brown-gray stem spot ( Diaporthe helianthi ),
anamorph ( Phomopsis helianthi ) and alternaria leaf blight ( Alternaria
helianthi ).
9.4.5 Novel Products
Biotechnology offers other potential improvement in the quality of sunflower
products and byproducts. The fatty acid composition of some sunflower
varieties has been modified through conventional plant breeding and
mutagenesis (Lacombe and Bervillé 2000). Although biotechnology could
overcome some of the restrictions in this area and pave the way for further
advances (Rousselin et al. 2002), its acceptance by the consumer market
must also be carefully considered. The high price of sunflower oil is due to
its being perceived as a healthy, high quality product (Chapter 1). Given
that consumers in many countries are opposed to GM food, diffusion of GM
varieties would probably affect its price and make sunflower products less
 
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