Novel Resources for Oilseed Rape Breeding Improving Harvest Index (NOVORB-HI)

Abstract

At the end of the season, the proportion of harvested product relative to the total above-ground biomass of the plant is termed the Harvest Index. In oilseed rape, this value is typically 0.2 - 0.25, which is around half that of crops such as wheat. This inefficiency in the production of seeds is thought to be largely a consequence of the architecture of the inflorescence of the plant, which impacts the properties of the canopy of the crop.

The genetic control of inflorescence/canopy architecture in oilseed rape is poorly characterised and likely to be complex. We aimed to improve our understanding of this control by conducting detailed morphological analyses of the inflorescence of oilseed rape, as grown in the field, along with quantitative genetic analyses. The study exploited a pre-existing mapping population derived from a cross between an old European variety of winter habit oilseed rape (Tapidor) and a Chinese cultivar of semi-winter habit (Ningyou 7).

This represents a cross between the genetic extremes available in oilseed rape (species Brassica napus). In addition, two new populations were developed and studied. These involved four relatively modern varieties adapted to UK conditions (Capitol x Rocket and Verona x Grizzly) and selected on the basis of exhibiting contrasting canopy architecture.

The results of our analyses showed there to be a wide range of variation for most of the inflorescence/canopy architecture traits measured. This was much greater in the population derived from the cross between European and Chinese material than in the new crosses between UK-adapted varieties. Despite the inherent environmental effects and errors associated with field data, major genetic components were identified for most of the traits.

The quantitative genetic analyses showed that the basis of this genetic component is complex, typically consisting of contributions from numerous different parts of the genome (loci), each having only a small effect. We tested whether the positions of these loci coincided with the positions of genes, identified from studies in Arabidopsis thaliana, which were candidates for potentially being involved in control of the traits. Some of these, including: TB-like, TCP and BLR, ('length traits'), GAI, RGL1 and MAX2 (branch and pod angle), BLR (fertile branch number and pod density), RGL1 (seed density and GAI (stem width), were coincident with the peaks of QTL (quantitative trait loci). These coincidences represent the bases for hypotheses to be tested in future studies.

Our study confirmed that canopy architecture in oilseed rape is under complex genetic control. We found evidence that some candidate genes arising from studies in other species may well have a role in the control of corresponding traits in oilseed rape, but for most we found no indication of involvement. Indeed, numerous loci influencing canopy architecture traits were identified that appear not to correspond to the positions of candidate genes.

Our results direct focus upon specific known genes that may be involved in the control of aspects of canopy architecture that are likely to impact seed yield. In addition, they indicate that studies conducted to date in A. thaliana, which used mutation-based approaches, ought to be supplemented with studies exploiting natural genetic variation in order to assist the identification of the genes underlying many of the important loci that we have identified in oilseed rape.