Environmental Conditions Affect Associations between Wheat Yield

The timing and duration of phenological events in wheat are important factors for adaptation and yield in a given environment. However, how important they are in the environmental conditions is a misunderstood issue. Associations between grain yield and phenological events in Iranian wheat cultivars were studied in Moghan region of Iran. Eighty-one wheat cultivars released from 1930 to 2006 were examined in 2010–2011 with normal sowing conditions and in 2013–2014 with late sowing conditions. Under both sowing dates, increasing anthesis thermal time up to special amount (1357 and 671 oC under normal and late sowing conditions, respectively) had positive effects on grain performance but these advantages disappeared with further increasing of anthesis thermal time. Grain filling duration positively correlated with grain yield under normal sowing conditions but the reverse trend was observed under late sowing conditions whereas increasing grain filling duration decreased main stem grain yield. There were positive links between spike filling rate and grain performance in both conditions tested, suggesting that spike filling rate could be a promising trait in wheat breeding program challenging with increasing grain yield.