Mycorrhizal inoculum production of Gigaspora gigantea in growing media and particle size
There is little information about the influence of particle size and the physical and chemical properties of the growing media used for mycorrhizal inoculum production. The objetive of this study was to evaluate the number of spores, root colonization, aerial and root dry biomass, and root volume produced by lettuce plants inoculated with Gigaspora gigantea in 12 substrates made with different size particles. Growing media were prepared with two types of coconut coir (Cocos nucifera): granular (Gc) and fibrous (Fc) mixed with pumice (P) and volcanic scoria (locally called tezontle T), with three granulometries (<0,-6 mm, 0.6-1 mm, 1-2 mm) in a ratio 3:1 v/v, except Gc:P:T (1-2 mm) in a ratio 6:1:1 v/v. The control treatment consisted of a mixture of peat:agrolite:vermiculite (Pe:A:V) in bulk material with a 2:1:1 v/v ratio. Lactuca sativa var. King Henry was used as host plant. The experiment was evaluated 75 d after sowing with an analysis of variance and comparison of means (Tukey≤0.05). The micromorphological study and image analysis determined the interaction of growing media-rootspores. The highest mycorrhizal colonization (p≤0.05) occurred in Pe:A:V in bulk materials, Gc:P:T 1-2 mm and with granulometry of 0.6-1 mm. The highest number of spores (20 spores g-1 dry growing medium) was obtained in Pe:A:V in bulk (p≤0.05). Growing media with particle size <0.6 mm and 0.6-1 mm positively favored the response variables of the host plant (p≤0.05). The micromorphological study showed that the spores are related to the components Gc:P:T and reside in the rough surface of the fractured vesicles of tezontle (volcanic residue). Growing medium of Gc:T:P (1-2 mm) is recommended as a substitute of Pe:A:V in bulk materials for the production of Gi gigantea.