A Look Under the Surface: Discovery of Genetic Variation for Root Traits in Brassica napus L

Oilseed rape (Brassica napus L.) is among the three most important oil crops in the world and plays an integral role in cereal crop rotations. Drought events are among the most important factors limiting yield in oilseed rape production. Especially in light of climate change, adaptation to low rainfall conditions is a major target of ongoing breeding programs. Very little is known about how oilseed rape roots maintain water uptake during rainless growth periods, for example by penetration into deeper soil or increasing the density of fine roots, however these traits are highly relevant to avoid yield losses under dehydration. Moreover, the reaction of the root system to nitrogen availability is also of great interest for increasing nitrogen use efficiency in oilseed rape.

In a large-container phenotyping system, comprising 120 wheelie-bins with 90 cm soil depth, we assessed genetic variation for several root traits in fully mature plants from two diversity sets of 30 genotypes each. The first panel broadly covered genetic variation present in the B. napus gene pool, including synthetic accessions and older varieties with high seed erucic acid and glucosinolate content. The second panel represents breeding progress in European commercial elite inbred and hybrid varieties, released to the market between 1989 and 2014. We discovered extreme variation for root traits within the gene pool of B. napus, providing unprecedented insight into important diversity for breeding. Besides a differentiation in soil volume penetration and root biomass, contrasting inverse reactions to nitrogen supply were observed in some accessions.