The true stem of grasses is located below the dividing mass of cells of the shoot apex (SA). This is the oldest tissue of the tiller and contains the oldest hyphae. These hyphae do not proliferate except among the dividing cells arising from point meristems that will give rise to adventitious roots (Fig. 14-19). Hyphae can be present in the tips of adventitious roots (Fig. 14-20) but apparently are absent elsewhere away from this apical region. The concentration and distribution of hyphae in the adventitious root tip remains the same as when the root first started developing within the stem. This indicates that no further hyphal colonization of the root can occur once the root meristem migrates away from the stem.

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Fig. 14-19. Transverse section through a basal ryegrass stem infected with hyphae of Epichloë festucae expressing GFP. Hyphae are present near the base, but not within the two roots (-->).

    

Fig. 14-20. Hyphae (-->) of Epichloë festucae expressing GFP in the tip of an adventitious ryegrass root.

 
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