Selection for seed dormancy within Bromus diandrus populations alters ABA1 and GA20ox gene expression

Context Bromus diandrus Roth is a serious weed of cereal-based cropping systems in South Australia. Its adaptation to local climate and production systems, prolific seed production and evolution of herbicide resistance have made this weed difficult to manage. Aims Studies were undertaken to determine genetic variation in seed dormancy within B. diandrus populations and its association with genes involved with gibberellic acid and abscisic acid synthesis. Methodology Seeds from five B. diandrus populations were sampled during 2017 from commercial fields and planted during 2018 in pots. Protracted seedling emergence in these populations allowed selection of low and high dormancy cohorts. Seeds produced by these cohorts from each population were evaluated for variation in seed dormancy in the following year. The process of cohort selection and seed dormancy evaluation was repeated. The mechanism regulating seed dormancy was investigated in 2020 by assessing seeds of low and high dormancy cohorts concurrently for dormancy and for expression of ABA1 and GA20ox genes, using quantitative real-time PCR. Results There was at least a two-fold difference in seed dormancy among populations collected from different farms. Low and high dormancy cohorts within each population maintained consistent differences in seed dormancy in both years of assessment, suggesting genetic control over this trait. Differences in seed dormancy between low and high dormancy cohorts were significantly correlated with ABA1 and GA20ox gene expression. Conclusions Large differences in seed dormancy exist between individuals in B. diandrus populations. The study has provided evidence of genetic variation for seed dormancy within B. diandrus populations, which was associated with ABA1 and GA20ox gene expression. Implications Presence of genetic variation for seed dormancy could play an important role in adaptation to escape pre-sowing weed-control tactics, meaning that B. diandrus could become an even greater problem in field crops grown in this region.