Fig. 4

Resistance mechanisms of sorghum to S. hermonthica 9 DAI. (Aa) Colonization of IS18829 showing a well-established haustorium at the point of attachment. The parasite is also fully vegetative and established vascular connections with the host. Scale = 0.5 cm. (Ab) Transverse section through IS18829 showing penetration of the root cortex and endodermis. Penetration resulted in vascular connection between the host and parasite xylem. Scale = 0.1 mm. H = host, P = parasite, Hx = host xylem, Px = parasite xylem, Hx-Px = host xylem connected to parasite xylem. (Aa) Colonization of N13 by Striga showing a poorly established parasite with a darkly stained haustorium, possible because of dead cells. Scale = 1 mm. (Bb) Transverse section through N13 tissue showing failure of the parasite to breach the host’s cortex. Scale = 0.1 mm. (Ca) Colonization of IS1097810978 showing a poorly developed parasite without vascular connection. Scale = 1 mm. (Cb) A transverse section through an embedded IS1097810978 root tissue showing successful penetration of the cortex but parasite blockage at the endodermis. Scale = 0.1 mm. (Da) Colonization of IS14963 showing an intense Hypersensitive Reaction (HR) at the site of parasite infection. Scale = 1 mm. (Db) A transverse section through an embedded IS14963 root tissue showing blockage of the parasite tissue due to HR at the host-parasite interphase. Scale = 0.1 mm. (Ea) Colonization of IS9830 showing the parasite penetrating host tissue but failing to establish vascular connections. The parasite instead emerges on the opposite side of the root. Scale = 1 mm. (Eb) A transverse section through an embedded tissue of IS9830 showing parasite penetration of the host root and subsequent emergence in the opposite direction. Scale = 0.1 mm