Arbuscular mycorrhizal fungus activates wheat physiology for higher reproductive allocation under drought stress in primitive and modern wheat

Arbuscular mycorrhizal fungus (AMF) can mediate physiological adaptation of higher plants to drought stress, including wheat. Yet, it is unclear how AMF affects reproductive output via mediating crop physiological vitality at the evolutionary scale. To clarify this issue, a growth environment-controlled experiment was conducted using four primitive wheat genotypes and four modern ones with or without AMF (Funneliformis mosseae) inoculation. Two water regimes (80 % and 40 % field water capacity, FWC80 (well-watered) and FWC40 (drought stress)) were included. The data indicated that AMF inoculation significantly improved leaf area, photosynthetic rate, stomatal conductance and water use efficiency under drought stress, compared to the non-AMF group (CK). Regardless of soil moisture, the relationship between reproductive biomass vs. vegetative biomass (R-V), and between leaf biomass vs. shoot biomass, all fell into a typical allometric pattern (α>1, P<0.001) in primitive wheat. In contrast, in modern wheat, the R-V relationship tended to an isometric pattern (α≈1, P<0.001), showing lower α values in all treatments relative to primitive ones. Furthermore, AMF inoculation significantly promoted the maintenance rate of yield and biomass under drought stress, suggesting greater drought tolerance as induced by AMF in modern wheat compared to primitive ones. These findings illuminated a key evolutionary strategy to enhance reproductive allocation via activating physiological activities under drought stress from primitive to modern wheat.