Transgenic Sunflower - Genetics, Genomics and Breeding of Crop Plants - page 299

the loss of certain of their parts, so it is therefore important to stop damage
as early as possible at the beginning of the attack.
Two beetles cause economically important damage in North America
(Charlet and Brewer 2001). Cylindrocopturus adspersus causes crop damage
mainly by lodging in weakened plants whose stems have been bored; this
also facilitates the development of fungi. This pest can be controlled by the
application of insecticides, though it would also be interesting to explore
the genetic resistance of many wild sunflower species. A similar situation
occurs with another Coleoptera, Smicronyx fluvus , whose larvae develop
inside seeds. This is an oligophagous species, which is adapted to only a
few hosts and can be controlled with insecticides, sometimes in combination
with crop traps. Some parasitic Hymenoptera and Diptera act as controllers,
and genetic resistance could, therefore, be achieved. Females consume head
bracts and pollen before oviposition, so the expression of the CpT1 gene in
these tissues would help to reduce adult populations. However, the
probability of transgene escape highlights the need for management
strategies that limit the induction of insect resistance and the acquisition of
transgenes by other wild host plants. This would provide durable resistance
without environmental impact.
9.4.4 Disease Control
Most research on sunflower crop production restraints have relied on a few
diseases caused by fungi ( Table 9-4 ). Although there are more than 30
reported pathogens, half of the CAB Abstracts indexed publications for
2002-2007 refer to only four. Of these, the polyphagous Sclerotinia
sclerotiorum has received the main attention because of the severe damage it
causes and the difficulty of controlling it. It is responsible for white rot and
attacks many plants, including soybean. There have been continuous efforts
to develop methods enabling early (Vuong et al. 2004) and advanced selection
(Becelaere and Miller 2004a, b) of lines expressing tolerance to Sclerotinia .
Although there does not seem to be a complete resistance (Pedraza et al.
2004), there is a strong genetic component that allows identification of
outstanding tolerant materials (Miller et al. 2006).
Research involving the heads of infected plants has shown that tolerance
to white rot is related to the accumulation of phenolic (Prats et al. 2003) and
coumarin compounds (Prats et al. 2006) and to the absence of the phytotoxic
effect of oxalic acid (Baldini et al. 2002). Oxalic acid concentration increases
when tissues are damaged and this can be used as an indirect method for
selecting on the basis of tolerance to disease (Vasic et al. 2002).
Biotechnology offers a number of strategies for the control of white rot
including defense activation, fungus inhibition, and detoxification (Schnabl
et al. 2002; Lu 2003). GM sunflower might present resistance to the damage