Abstract

The parasitic Striga hermonthica weed causes serious yield losses to maize (Zea mays L.) in sub-Saharan Africa. Striga seeds are stimulated to germinate by strigolactones produced by the host plants. Maseno EH14 and EH11 hybrid maize varieties have been bred for Striga and foliar diseases tolerance respectively but their tolerance mechanisms have not been elucidated. The study investigated the activity and chemical composition of root exudates of the maize varieties alongside a Striga susceptible PHB3253 variety on Striga seed germination. Germination assays were carried out using crude maize root exudates alongside the synthetic GR24 stimulant. Germination frequencies and radicle lengths were analyzed using ImageJ v. 1.45. Data were subjected to ANOVA through the linear model of SAS and means were separated using LSD_0.05. The root exudates were also freeze-dried and subjected to HPLC analysis. Maseno EH14 had the lowest Striga seed germination at 20.08% compared to PHB3253 at 51%, EH11 at 37.54% and GR24 at 76.96%. Maseno EH14 also had the shortest radicle length at 0.38 mm against PHB3253 at 0.82 mm, EH11 at 0.71 mm, and GR24 at 0.91 mm. HPLC analysis showed PHB3253 and Maseno EH11 exuding mainly 5-Deoxystrigol and two other compounds while EH14 had three peaks that did not correspond to any of the standard strigolactones used in the analysis. Maseno EH14 therefore exhibits tolerance to Striga hermonthica due to low stimulation of Striga seed germination, and the absence of the more stable 5-Deoxystrigol strigolactone which is commonly associated with Striga susceptibility in maize.

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