Assessing the genetic relatedness of higher ozone sensitivity of modern wheat to its wild and cultivated progenitors/relatives

Modern wheat (Triticum aestivum L.) is one of the most ozone (O-3)-sensitive crops. However, little is known about its genetic background of O-3 sensitivity, which is fundamental for breeding O-3-resistant cultivars. Wild and cultivated species of winter wheat including donors of the A, B and D genomes of T. aestivum were exposed to 100 ppb O-3 or charcoal-filtered air in open top chambers for 21 d. Responses to O-3 were assessed by visible O-3 injury, gas exchange, chlorophyll fluorescence, relative growth rate, and biomass accumulation. Ozone significantly decreased light-saturated net photosynthetic rate (-37%) and instantaneous transpiration efficiency (-42%), but increased stomatal conductance (+11%) and intercellular CO2 concentration (+11%). Elevated O-3 depressed ground fluorescence (-8%), maximum fluorescence (-26%), variable fluorescence (-31%), and maximum photochemical efficiency (-7%). Ozone also decreased relative growth rate and the allometric coefficient, which finally reduced total biomass accumulation (-54%), but to a greater extent in roots (-77%) than in the shoot (-44%). Winter wheat exhibited significant interspecies variation in the impacts of elevated O-3 on photosynthesis and growth. Primitive cultivated wheat demonstrated the highest relative O-3 tolerance followed by modern wheat and wild wheat showed the lowest. Among the genome donors of modern wheat, Aegilops tauschii (DD) behaved as the most O-3-sensitive followed by T. monococcum (AA) and Triticum turgidum ssp. durum (AABB) appeared to be the most O-3-tolerant. It was concluded that the higher O-3 sensitivity of modern wheat was attributed to the increased O-3 sensitivity of Aegilops tauschii (DD), but not to Triticum turgidum ssp. durum (AABB) during speciation.