Genotype × environment interaction studies highlight the role of phenology in specific adaptation of canola (Brassica napus) to contrasting Mediterranean climates

While genotype (G) × environment (E) interaction (G × E) complicates broad crop adaptation, understanding its causes facilitates breeding for specific adaptation. South-western Australia captures a broad range of Mediterranean climates, from a very warm short season with low rainfall in the north and east to a longer season with high rainfall in the southwest, and provides a unique opportunity to investigate G × E interaction. In this study, we evaluate G × E interaction for seed yield and oil content of canola genotypes with wide ranging phenology across south-western Australia.Environments were separated into year (Y) and location (L) and a factor analytic (FA) model used to partition G × E interactions into G × Y, G × L and G × Y × L across four years (2006–2009). G × E interaction contributed 34% to total variance of seed yield compared with 9% for G. An additive main effects and multiplicative interaction (AMMI) model was used to further evaluate the significance of G × L, and delineate mega-environments (ME) and determine the best performing cultivar in each year. AMMI identified two MEs with different seasonal climates. ME1 combines >330 mm seasonal rainfall with a cooler, longer post-anthesis growing period. ME2 is more terminally drought-prone, with higher temperatures and <300 mm rainfall, resulting in a short growing season. There were significant crossover yield responses to location changes: the medium flowering genotypes produced significantly higher yield than the early flowering genotypes in ME1 but yielded poorly in ME2, and vice versa. In contrast to yield, G effects were very strong in oil content, accounting for 53% of total variance, compared with 14% for G × Y, and negligible G × L effects. Finlay–Wilkinson regression showed little crossover interaction in oil content with E. The key outcome of this G × E interaction study is the importance of phenology to the adaptation of canola in south-western Australia. Therefore, it is suggested that breeding for specific adaptation to each mega-environment should be targeted with a breeding strategy focusing on drought and heat tolerance in ME2 and high yield potential in ME1.

► Seed yield and oil content of canola genotypes and their interactions with environment were investigated.
► Significant genotype crossover yield responses to environment but little G × E interaction effect on oil content.
► The medium flowering genotypes produced higher yield than the early flowering ones in the high rainfall areas but yielded poorly in the low rainfall areas, and vice versa.
► Two mega-environments were identified for targeted breeding in south-western Australia.