Propagation and storage of vesicular–arbuscular mycorrhizal fungi isolated from Saskatchewan agricultural soils

Factors affecting the propagation of vesicular–arbuscular mycorrhizal fungi (VAMF) Glomus clarum, Glomus mosseae, and Glomus versiforme isolated from Saskatchewan soils were assessed in growth-chamber studies. Initially, lentil (Lens esculenta L.), maize (Zea mays L.), and a sorghum (Sorghum bicolor (L.) Moench) and sudangrass (Sorghum sudanense (Piper) Hitch.) hybrid were inoculated with G. clarum and grown in 2 or 6 kg of soil–sand (1:1) substrate until maturity. All three crops supported growth and spore production by G. clarum, but the maize plant yielded the largest number of spores. The ability of G. clarum to produce large numbers of spores reflects either an inherent ability of this VAMF strain to sporulate or a favorable interaction (related to spore production) with a maize host crop. Twice as many G. clarum spores per gram of soil–sand substrate were obtained from 2-kg pots compared with 6-kg pots. Enhanced spore production in the smaller pots was related to poor plant growth and, apparently, nutrient stress. Plants grown in 2-kg pots were stunted, yielded less biomass, and exhibited severe symptoms of P and N deficiency. Monospecific cultures of G. clarum, G mosseae, and G. versiforme were produced using maize plants grown in 2-kg pots. Under these conditions the level of spore production was G. clarum > G. versiforme > G. mosseae. Storage of the VAMF inoculants at 7 °C, compared with 25 °C, enhanced spore viability. This was evident from a reduction in VAMF colonization and spore production in wheat (Triticum aestivum L.) and the sorghum–sudangrass hybrid plants inoculated with G. mosseae spores stored at 25 °C. Osmotic stress exerted on G. mosseae spores during density-gradient centrifugation had no effect on their viability. Key words: vesicular–arbuscular mycorrhizal fungi, Glomus spp., host crops, substrate mass, nutrient stress.