Arbuscular mycorrhizal fungi (AMF) improved water deficit tolerance in two different sweet potato genotypes involves osmotic adjustments via soluble sugar and free proline

Sweet potato (Ipomoea batatas (L.) Lam.) is one of the most important carbohydrate rich crops and provides nutritional value-added products. However, its growth and yield is limited by water availability, especially in the rain-dependent zones. The present study investigated the role of arbuscular mycorhizal fungi (AMF) in improving the growth and yield in two cultivars of sweet potato (Tainung 57 and PROC 65-3) under water deficit (WD) and elucidates the morphological and physiological changes upon AMF-inoculation. Root colonization in AMF inoculated sweet potato under well watering was demonstrated in both cv. Tainung 57 (57.72%) and cv. PROC 65-3 (68.75%) and it declined when subjected to water deficit condition, indicating susceptibility to drought conditions. Phosphorus content in AMF inoculated cvs. Tainung 57 and PROC 65-3 were enriched by 8.3 and 5.7 mg g(-1) DW, respectively, more than those in the AMF un-inoculated plants. Free proline and soluble sugars play a key role in WD-stressed plants with AMF-association by adjusting osmotic potential. In PROC 65-3, free proline and soluble sugars in the leaf tissues of AMF-inoculated plants under 17.5% soil water content (SWC) were maximized (6.27 mu mol g(-1) FW and 53.94 mu g g(-1) DW, respectively). A positive correlation was revealed between osmotic potential and osmolyte accumulation. Leaf osmotic potential (psi(s)) in plants without AMF-inoculation grown under WD condition declined, leading to total chlorophyll degradation. In contrast, this was enhanced in AMF-inoculated plants under water deficit conditions, leading to increased content of photosynthetic pigments, enhanced maximum quantum yield of PSII (F-v/F-m) and photon yield of PSII (phi(PSII)), increased net photosynthetic rate and growth characteristics. Moreover, the numbers of tubers per plant and tuber fresh weight in AMF-inoculated sweet potato plants under WD stress were significantly increased, especially in cv. Tainung 57 (water deficit sensitive). The study concludes that inoculation of AMF in sweet potato plants improves plant growth characteristics and enhances water deficit tolerance via soluble sugars and free proline accumulation. (C) 2015 Elsevier B.V. All rights reserved.