The role of strigolactone structural diversity in the host specificity and control of Striga, a major constraint to sub‐Saharan agriculture

Abstract

Social Impact StatementThe parasitic weed Striga affects crops such as sorghum, maize, millet, and rice in over 40 countries on the African continent and negatively impacts the livelihood of over 300 million small‐holder farmers. Striga seeds can remain dormant in the soil for many years until they are triggered to germinate by germination stimulants, called strigolactones, exuded from the roots of their host. Here, the current knowledge on the biosynthesis of the strigolactones, their structural diversity, and biological relevance are reviewed. This knowledge could improve Striga control and thus improve the livelihood of small‐holder farmers.SummaryThe parasitic plant genus Striga causes major yield losses to several crops such as sorghum, millet, and rice in arid and semi‐arid regions of the tropics. For Striga to successfully parasitize its host plant, two conditions should be fulfilled: suitable germination conditions and the presence of a host plant that exudes so‐called germination stimulants, strigolactones, that are also as a signal to attract beneficial micro‐organisms such as arbuscular mycorrhizal (AM) fungi. Different plant species exude qualitatively and quantitatively different blends of strigolactones, and this plays a key role in determining Striga host specificity. Sorghum lgs1 genotypes with a mutation in a sulfotransferase (SbSOT4A), for example, exude orobanchol and are resistant to Striga, while 5‐deoxystrigol is the major strigolactone exuded by susceptible cultivars with wild type SbSOT4A. In this review, we discuss the current knowledge on the biosynthesis of the large diversity of strigolactones, how SbSOT4A may be involved in this, and how strigolactone diversity may contribute to microbiome recruitment. Finally, we discuss how knowledge on the importance of strigolactone diversity can contribute to Striga control.