Hyphae within the SAM (Fig. 14-12 and 14-13) extend into leaf primordia, the meristematic tissues from which new leaves develop (Philipson and Christey, 1986). The endophyte then colonizes the leaf as it develops. New tillers start as axillary buds that develop on the SAM (Fig. 14-14, 14-15, and 14-16). One axillary bud is formed each time a leaf is initiated. The hyphae of the endophyte, typically, but not always, grow into each axillary bud and henceforth colonize each new tiller. If hyphae fail to colonize the leaf primordium or axillary meristem, the leaf or tiller, respectively, will remain endophyte free. Hyphae also colonize the inflorescence when it begins development at the tip of the SAM (Fig. 14-17 and 14-18), enabling infection of the developing seed and thus vertical transmission to the next generation of plants.
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Fig. 14-12. Longitudinal section of the shoot apical meristem of a mature tiller of a ‘Resolute' tall fescue plant infected with Neotyphodium coenophialum (-->). |
Fig. 14-13. The shoot apical meristem of a mature tiller of a ‘Resolute' tall fescue plant infected with Neotyphodium coenophialum (-->) at higher magnification. |
Fig. 14-14. Transverse section through the base of a ryegrass tiller showing the shoot apical meristem (S) from which leaves arise. |
Fig. 14-15. The shoot apex within an axillary bud on a mature tiller of a ‘Resolute' tall fescue plant infected with Neotyphodium coenophialum. Numerous hyphae (-->) are present within the shoot apex and the young leaves. |
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Fig. 14-16. Closer view of the numerous hyphae (-->) shown in Fig. 14-15. |
Fig. 14-17. A young ryegrass inflorescence forming at the tip of the shoot apical meristem. |
Fig. 14-18. The same inflorescence (as Fig. 14-17) viewed using fluorescent microscopy showing that it is extensively colonized with hyphae of a GFP-expressing Epichloë festucae strain. |
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