Quantitative development of Paris-type arbuscular mycorrhizas formed between Asphodelus fistulosus and Glomus coronatum.

•  Arum- and Paris-type symbioses are the two main morphological types of arbuscular mycorrhiza. Here, the developmental time-course of the Paris-type association formed from colonization of Asphodelus fistulosus (onion weed) by Glomus coronatum is presented. •  Development was monitored over 27 d. Root colonization was assessed using a modification of the magnified intersects technique (MIT), for investigating the interdependence (thus IMIT) of structures. •  Hyphal and arbusculate coils were found predominantly in the outer and inner cortex of the root, respectively. The interdependence of external hyphae, hyphal coils and arbusculate coils was determined during the relatively slow development of the symbiosis. •  The time required for development of Paris-type arbuscular mycorrhizas is slower than for the Arum type, and both time and space influence the formation of hyphal coils. Use of IMIT for scoring colonization allows determination of the interdependence of different fungal structures, and thus the technique has potentially wide applications, such as in relating the presence of different structures to signals from molecular probes.