Anatomical study on the interaction between the root endophytic fungus Heteroconium chaetospira and Chinese cabbage

Abstract

Chinese cabbage roots colonized by the dematiaceous fungal taxon Heteroconium chaetospira were previously found to become highly resistant to clubroot and Verticillium yellows. The dematiaceous fungus possesses an endophytic nature, but no detailed anatomical studies on endophyte-host plant interactions have so far been provided. Light and electron microscopy revealed that hyphae of H. chaetospira were abundant on and inside the root epidermal cells by 3 weeks following inoculation. The penetration pegs easily breached into epidermal cells, and the infection hyphae penetrated into cortical cells. Some appressorium-like swollen structures formed from intracellular hyphae, but no visible degradation of the host cell walls was evident where the hyphae contacted. No visible signs of host reactions and no invagination of the host plasma membrane around the hyphae were seen in the host cells. By 8 weeks following inoculation, masses of closely packed fungal cells had been formed in some cells of the epidermis and cortical layers, but further hyphal ingress was halted, mostly in the inner cortical cell layer. Thus, root vascular cylinders remained intact.

Beneficial endophytic microorganisms of Brassica – A review

“…A number of detailed microscopy studies on the infection process by this endophyte have been undertaken (Ohki et al, 2002;Yonezawa et al, 2004) where it was observed that, in the root tip region of B. napus and B. rapa plants, the fungus produced an appressoria-like structure on the cell surface before entering and colonising cortical cells. No visible signs of host reactions and no invagination of the host plasma membrane around hyphae were seen (Yonezawa et al, 2004) and the endophyte subsequently formed distinctive structures made from aggregations of mycelium (microsclerotia) inside the host epidermal roots Ohki et al, 2002). Beneficial attributes for the host plant, conferred by the endophyte, include plant growth promotion and reduced disease symptoms caused by a number of pathogens including Alternaria spp., P. brassicae, Pseudomonas syringae pv.…”

“…Researchers investigating the biology of this fungus often use baiting techniques, such as planting seedlings of Chinese cabbage, barley, rape or rhododendron in soils suspected of harbouring the endophyte (Narisawa et al, , 1998 with woodland, field and forest soils in Japan and Canada, found to be favourable so far (Usuki and Narisawa, 2007). A number of detailed microscopy studies on the infection process by this endophyte have been undertaken (Ohki et al, 2002;Yonezawa et al, 2004) where it was observed that, in the root tip region of B. napus and B. rapa plants, the fungus produced an appressoria-like structure on the cell surface before entering and colonising cortical cells. No visible signs of host reactions and no invagination of the host plasma membrane around hyphae were seen (Yonezawa et al, 2004) and the endophyte subsequently formed distinctive structures made from aggregations of mycelium (microsclerotia) inside the host epidermal roots Ohki et al, 2002).…”

“…,Yonezawa et al (2004) Leptosphaeria biglobosa B. napus Plant growth promotion and antifungal activity towards S. sclerotiorum…”

Xylariales): Physiological characterization and structural features of its association with wheat.

“…Here, no defense responses were found when the interaction between T. aestivum and M. bolleyi was studied with TEM, only an electronically dense material was observed around the intercellular hyphae. This is similar to fibrillar material observed surrounding the hyphae in Chinese cabbage in the presence of Heteroconium chaetospira (Yonezawa et al, 2004) and in Asparagus officinalis inoculated with P. fortinii (Yu et al, 2001). Although in the current study the fibers were not observed, it could be due to an inefficient fixation of the material.…”

Heteroconium chaetospira, a dark septate root endophyte allied to the Herpotrichiellaceae (Chaetothyriales) obtained from some forest soil samples in Canada using bait plants

“…The ability of H. chaetospira to colonize and grow as an endophyte in healthy roots has been demonstrated previously using Chinese cabbage (Ohki et al 2002;Yonezawa et al 2004;Hashiba and Narisawa 2005) and rhododendron (Usuki and Narisawa 2005); these studies were based on isolates obtained from soil samples from Japan baited with herbaceous plants. There were prior reports of this species from the roots of Ammophila arenaria (L.) Link collected in the UK (IMI 60911) (Domsch et al 1980) and a smaller-278 spored variety, described by Bourchier as Septonema chaetospira var.…”