Penalties in yield and yield associated traits caused by stem lodging at different developmental stages in summer and spring foxtail millet cultivars

Foxtail millet [Setaria italica (L.) Beauv.], a soft-stemmed cereal crop, suffers from severe stem lodging in many production regions. However, the effects of stem lodging on grain yield and its related traits in this crop have not been reported. In the 2014 and 2015 cropping seasons, two field experiments were separately conducted to evaluate the impacts of stem lodging on summer and spring foxtail millets. Transient and permanent lodging treatments were applied by artificially bending the culms at 10, 20, and 30 days after anthesis (DAA). Plants that received transient lodging treatment were bent for 24 h and then allowed to return to a vertical position naturally, and plants designated for permanent lodging treatment were bent to about 80° from the scheduled dates to maturity. Both lodging treatments caused obvious yield reductions in summer and spring foxtail millet cultivars. Up to 19.3% and 25.0% grain yield reductions were caused by the transient lodging treatment, and up to 41.2% and 51.1% yield reductions were induced by the permanent lodging treatments for the summer and spring cultivars, respectively. The yield losses in the lodging-resistant cultivars of both summer and spring ecotypes caused by the permanent lodging treatments were less than the lodging-susceptible cultivars in 10 and 20 DAA. The most sensitive plant developmental stage to the transient lodging treatment was the grain filling stage (i.e., early to late milk stage), while yield reductions proportional to the developmental stages at the onset of the permanent lodging treatment also were observed. Correlation analysis and principle component analysis demonstrated that panicle weight and grain weight per panicle were the most important yield-related traits affected by the lodging treatments. Lodging treatments did not have any obvious impacts on panicle length. The effects of stem lodging on 1000-grain weight varied in different cultivars. Lodging treatments also caused reductions in biomass of whole plant and the stalk, as well as harvest index, at certain dates when the treatments were applied. This study provides the first direct estimation of the effects of stem lodging on grain yield and yield-related traits in foxtail millet.