4.4 Genetic understanding of waterlogging tolerance
Our results showed that most of currently available Australia barley genotypes are intolerant to waterlogging. It is thus crucial that further scientific endeavour is undertaken to develop more waterlogging tolerant genotypes that alleviate yield losses caused by waterlogging.
Our previous studies have identified QTL controlling root AF under waterlogging stress, which is one of the major mechanisms for waterlogging tolerance in barley (Zhang et al., 2016). This gene was introgessed into a commercial variety Macquarie through repeated backcrossing. Although we did not measure AF (e.g. scored the proportion of aerenchyma based on digital images), because this has been done in many previous studies (Zhang et al., 2015; Zhang et al., 2016). Our results showed that Macquarie+ was the most tolerant to waterlogging (Fig. 2a, b); this result was mainly a consequence of higher numbers of spikes/m2 and to a lesser extent maintenance of grain weight under waterlogging (Fig. 3). Macquarie+ outperformed other varieties in most case and for most waterlogging treatments. The QTL for AF mitigated around 23% yield loss under waterlogging stress, suggesting that the QTL is effective in improving waterlogging tolerance of commercial varieties and can be used in breeding programs.