plant surface microbiology.pdf

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Ingrid Kottke
Fig. 1. Ectomycorrhiza formation by Laccaria amethystea and Picea abies. Longitudinal
section through an early state mycorrhiza. Hyphal attachment to root hairs (arrowhead)
without changes of hyphal morphology; hyphal attachment to root surface followed by
hyphal enlargement (arrow) and lobe-like growth of hyphae (double arrow); typical
Hartig net structure established between root cortical cells down to the endodermis
(scale 15 mm). cc Cortical cell, e endodermis, hs hyphal sheath, Hn Hartig net, rh root hair
tig net, the cuticle-like layer has to be penetrated by the hyphae. This process
has not been shown before and may be considered as a locally restricted
aggressive or saprophytic phase during ECM formation.
2 Long and Short Roots of Ectomycorrhiza-Forming Plants
Ectomycorrhizas are exclusively formed by perennial, woody plants belonging
to Pinaceae or to distinct families within the Rosidae (sensu “Angiosperm
Phylogenetic Group”, Bremer et al. 1998). The root system of these ECMforming
plants is divided into main, or “long roots” of relatively fast and
unlimited growth and secondary “short roots” of slow and limited growth
(Noelle 1910; Clowes 1951; Marks and Foster 1973). Ectomycorrhizae are typically
formed on short roots. However, long roots may become mycorrhizal
after turning into a resting stage (Wilcox 1968b). It was speculated that the
growth rate of hyphae might not compete with the growth rate of long roots,
thus preventing mycorrhiza formation (Marks and Foster 1973). However, sig-