Development of Infection by a Vesicular–arbuscular Mycorrhizal Fungus in Brassica Napus L. And Trifolium Subterraneum L.

Summary The sequence of stages involved in the development of infection by Glomus caledonium (Nicol. & Gerd.) Trappe & Gerd. in Brassica napus L. (spring rape) and Trifolium subterraneum L. (subterranean clover) was examined. When plants grown at similar relative levels of phosphate were compared, B. napus reduced the rate of all stages of the processes leading to colonization. Although maximum values of germination, hyphal extension, and appressorial formation and adhesion were similar in B. napus and T. subterraneum, in B. napus fewer appressoria produced penetration pegs and some penetration pegs failed to initiate colonies. In addition, in B. napus only a third of the colonies possessed arbuscules whereas in T. subterraneum all colonies had arbuscules. The rate of death of epidermal and cortical cells was similar between the species and did not explain the reduced colonization of B. napus. Chemical rather than physical factors associated with B. napus appeared to be involved in reducing the rate of development of each growth stage.