seed supply

Seed Systems Research Abstracts from the Biotechnology, Breeding and Seed Systems Conference

Alternative biotechnologies for controlling Striga: the next generation

New biotechnologies will be needed for Striga control. The IR-maize seed treatment technology is an excellent stop-gap technology; but it too can be perfected by controlled slow release formulation of the herbicides used so as to prevent phytotoxic concentration of herbicide near the crop root in low rainfall conditions, or washout of the herbicide in high rainfall, as well as to extend the duration of control needed for long season maize. Other herbicide resistant genes could be introduced/stacked; based on work with Orobanche and transgenic crop; inhibitors of EPSP-synthase (glyphosate) and dihydropteroate synthase (asulam) should be effective. Additionally, work on Orobanche seedlings and tissue cultures indicated that herbicides affecting cellulose synthase as well as tubulin polymerization severely inhibited the parasitic weed. Crops with target site resistance should allow control. Stacked genes for herbicide resistances would allow the use of herbicide mixtures, which would delay the inevitable evolution of resistance. The promising results of putting toxin genes behind a wound-inducible promoter in the crop have been obtained with parasitic Orobanche and could be tested with Striga and the crops affecting it. Too little is known about the pathway(s) of biosynthesis of Striga germination stimulation; whether one or more stimulants are produced, and whether from the same precursors. Should there be a single precursor, and should the pathway not be required for vital functions, it could be suppressed by RNAi or antisense technologies. The fact that random gene suppression by transposon tagging has not elucidated a Striga resistant mutant suggests that this may be a futile hope. Native microorganisms pathogenic on Striga have been proposed as biocontrol agents (mycoherbicides, bioherbicides), but none seem to be sufficiently virulent for controlling Striga in row crop situations. Such organisms can be augmented with transgenes for hypervirulence that would interfere with the Striga hormonal balance and/or that secrete toxins toxic to the parasite, as has been done with mycoherbicides for Orobanche. Additional genes could be introduced to produce ethylene to stimulate Striga germination. We proposed a strategy to debilitate Striga designed to lead to its self control. This would entail developing transgenic Striga with high copy number transposons carrying suppressed kev genes, i.e. deleterious transposons (DTs) which will quickly spread the gene to field populations because S. hermonthica is an obligate outcrosser requiring exogenous pollination. The kev genes could be turned on by a chemical inducer applied by the farmer or a novel compound produced by a transgenic variant of the crop.