CO2 exploitation and genetic diversity in winter varieties of oilseed rape (Brassica napus); varieties of tomorrow

We investigated the CO_2] exploitation and genetic diversity inthree old and three new winter varieties of oilseed rape (Brassicanapus L.). Plants were cultivated in growth chambers with 360 ppmCO₂ and 700 ppm CO₂ under conditions simulating a normalgrowth season. Exposed to elevated CO₂ the stomatal conductance(g_s) and the maximum photosynthesis capacity (A_max) werereduced and the dry biomass and the total seed-number were increased.The response in seed-yield differed among the varieties; it was increased inthree varieties and decreased in three. The analysis of variance (ANOVA)showed that there were Treatment- and Week-effects on the g_s, andthere were Variety-, Week- and Treatment-effects on the A_max. Itwas also evident that there were a Variety- and Variety-agegroup-effect onthe seed-yield, but the Variety-agegroup-effect could not explain theVariety-effect. When either or both covariates (seed-number andbiomass) were included in the model, the covariates themselves had asignificant effect and it became evident that there was a Treatment-effecton the seed-yield.From AFLP (amplified fragment length polymorphism) markers adendrogram was constructed by the UPGMA method (unweightedpair-group method using the arithmetic averages) and [G_ST wascalculated for all possible subsets of the varieties. The three old varietiescomprised the densest cluster and were also more genetically diverse thantwo of the three new varieties. Varieties with clear changes amongCO₂ levels were rather genetically diverse.Thus, the varieties represent different traits, which could be exploited infuture breeding of oilseed rape.