Abiotic and biotic stress tolerance in wheat: the role of arbuscular mycorrhizal fungi

Rhizospheres of crop plants are complexes of chemical and microbial interactions. Many plants produce allelochemicals, substances that inhibit growth of other plants and microorganisms. In previous research, colonization of Echinacea purpurea by beneficial mycorrhizal fungi appeared to alleviate the effects of allelochemicals on the growth and the development of the medicinal herb (Gualandi, 2010). The overall aims of the work reported here were to determine if colonization by arbuscular mycorrhizal fungi (AMF) alters responses of common wheat (Triticum aestivum) to abiotic [allelopathic effects of sorghum (Sorghum bicolor)] and biotic [bird-cherry oat aphid (Rhopalosiphum padi) (BCOA) and Bipolaris species(Bs)] stress. In all greenhouse experiments, wheat seed were planted into each of four treatments: 1) control (no-mycorrhizae, no-sorghum); 2) NM (no-mycorrhizae, sorghum); 3) Gm (AMF, Gigaspora margarita, previously propagated on sorghum); and 4) Gi (AMF, Glomus intraradices, previously propagated on sorghum). Sorghum allelopathy was not alleviated by AMF colonization. In all studies, control wheat plants had greater biomass (e.g., fresh shoot and root weight) than plants in all other treatments. Furthermore, biomass of wheat seedlings colonized with AMF (either Gm or Gi treatments) was not different from plants grown after sorghum but without mycorrhizae (NM). In two natural infestations, mycorrhizal plants were less preferred by R. padi than non-mycorrhizal (NM) plants or control plants, but this preference was not reproducible in controlled studies. Treatment had no effect on fall armyworm (Spodoptera frugiperda) larvae feeding behavior in laboratory assays. In growth chamber studies, inoculation with Bs had no effect on disease rating or growth of mycorrhizal and NM wheat seedlings. Our results indicate that AMF are not effective agents for control of abiotic (sorghum allelopathy) or biotic (herbivory by BCOA or reduction of plant vigor caused by Bs) stress; however variability in all studies was high so further research is needed before their use for these purposes is dismissed