Wheat-kernel growth characteristics during exposure to chronic ozone pollution

Chronic exposure to ozone (O 3) air pollution can reduce yield in wheat; however, little is known concerning the effects of O 3 stress on kernel development. A field study was conducted to investigate the effects of chronic O 3 exposure on kernel-growth components of two soft red winter-wheat genotypes (Seven and MD5518308). Five air-quality treatments, including charcoal-filtered air (CF), non-filtered air (NF), NF + 20, NF + 40, and NF + 80 nl O 3 liter −1 air were applied 4 h d −1, 5 d wk −1 through maturity. In the case of the NF + treatments, O 3 was added to existing ambient O 3 levels. Spike samples were collected 16, 20, 24, 28, and 32 days after anthesis (DAA). Linear and quadratic equations were fitted to kernel-weight data to estimate kernel-growth rate (KGR) and kernel-fill duration (KFD). Effective filling period (EFP) and assimilate utilization (AU) were also determined. Rates of growth for individual kernels were 0·74 mg d −1 and 1·07 mg d −1 for the NF + 80 and CF treatments, respectively. The NF + 80 nL litter −1 O 3 treatment significantly reduced KGR and AU compared with the CF treatment. Severn had a significantly loger KFD than MD5518308, but O 3 had no significant effect on KFD of either genotype. Each genotype had similar EFP values, and O 3 had no significant effect on EFP. Linear relationships between O 3 exposure and kernel weight suggests that O 3 effects on kernel weight begin soon after anthesis in MD5518308, but, in Severn, O 3 has a greater effect on kernel weight during the later stages of kernel development. These data suggest that decreased economic yield associated with chronic O 3 exposure is primarily the result of decreased KGR.