Relation between pectic substances and arbuscular mycorrhizal fungus infection in three vegetable crops

Abstract

The relation between pectic substances level and arbuscular mycorrhizal (AM) fungus infection in seedling roots of asparagus (Asparagus officinalis L. var. altilis, cv. MW500W) Welsh onion (Allium fisturosum L., cv. Green-negi), and petsai (Brassica campestris L., cv. Harumaki-gokuwase) was investigated to seek an effective inoculating method for AM fungus infection in host roots. The levels of total pectic substances were higher in storage roots of asparagus, root tips of both asparagus and Welsh onion, and both the secondarily branched root and main root of petsai, which are difficult to infect, than in the easy-to-infect primary feeder root of asparagus and both the primarily branched root and main root of Welsh onion. Pectic substances in the cortex of the storage root of asparagus and the secondarily branched root of petsai, and in the root tips of both asparagus and Welsh onion become heavily stained with ruthenium red, whereas the cortex of the primary feeder roots of asparagus and both the primarily branched root and main root of Welsh onion did not. The middle lamella and primary cell walls of root tissues are ruthenium red-sensitive. The lack of infection in asparagus storage roots and petsai branched roots is attributed to rich pectic substances in their thick middle lamellae and primary cell walls, so that the roots were infected with AM fungus (Gigaspora margarita) after pectinase treatment prior to the inoculation. These facts suggest that pectic substances in root tissues influence infection of AM fungus.