The role of strigolactones in resistance, tolerance and control of Striga infection in Sorghum

In sub-Saharan Africa the root-parasitic weed Striga, is among the most serious pests attacking the main grain crops. Satisfactory control is still out of reach and Striga is considered a threat to food security in the region. Resistance and tolerance to this parasite are valuable traits to reduce the burden. For germination, Striga seeds require the presence of strigolactones (SLs), a plant hormone and signaling molecules that is secreted by the host into the rhizosphere. In his thesis, using a combination of lab, greenhouse and field experiments, Nasreldin Mohemed investigated the role of SL composition and amount in Striga control in sorghum. In addition, he assessed the role of SLs in the suitability of millet, sesame and groundnuts as rotation and/or trap crop to reduce infection of sorghum by Striga and control its seed bank. He found a number of SLs that have not been reported before in these inter/rotation crops, thus explaining their suitability for Striga control and showed that in sorghum strigolactone composition is linked to low germination resistance as well as tolerance to Striga. This knowledge will provide the basis needed for further improving Striga resistance, tolerance and control in the important African staple food sorghum.</p

Genetic variation in Sorghum bicolor strigolactones and their role in resistance against Striga hermonthica

Sorghum is an important food, feed, and industrial crop worldwide. Parasitic weeds of the genus Striga constitute a major constraint to sorghum production, particularly in the drier parts of the world. In this study we analysed the Striga germination stimulants, strigolactones, in the root exudates of 36 sorghum genotypes and assessed Striga germination and infection. Low germination-stimulating activity and low Striga infection correlated with the exudation of low amounts of 5-deoxystrigol and high amounts of orobanchol, whereas susceptibility to Striga and high germination- stimulating activity correlated with high concentrations of 5-deoxystrigol and low concentrations of orobanchol. Marker analysis suggested that similar genetics to those previously described for the resistant sorghum variety SRN39 and the susceptible variety Shanqui Red underlie these differences. This study shows that the strigolactone profile in the root exudate of sorghum has a large impact on the level of Striga infection. High concentrations of 5-deoxystrigol result in high infection, while high concentrations of orobanchol result in low infection. This knowledge should help to optimize the use of low germination stimulant-based resistance to Striga by the selection of sorghum genotypes with strigolactone profiles that favour normal growth and development, but reduce the risk of Striga infection.</p