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 in three old and three new winter varieties of oilseed rape (Brassica napus L.). Plants were cultivated in growth chambers with 360 ppm CO₂ and 700 ppm CO₂ under conditions simulating a normal growth season. Exposed to elevated CO₂ the stomatal conductance (g_s) and the maximum photosynthesis capacity (A_max) were reduced and the dry biomass and the total seed-number were increased. The response in seed-yield differed among the varieties; it was increased in three varieties and decreased in three. The analysis of variance (ANOVA) showed that there were Treatment- and Week-effects on the g_s, and there were Variety-, Week- and Treatment-effects on the A_max. It was also evident that there were a Variety- and Variety-agegroup-effect on the seed-yield, but the Variety-agegroup-effect could not explain the Variety-effect. When either or both covariates (√seed-number and √biomass) were included in the model, the covariates themselves had a significant effect and it became evident that there was a Treatment-effect on the seed-yield. From AFLP (amplified fragment length polymorphism) markers a dendrogram was constructed by the UPGMA method (unweighted pair-group method using the arithmetic averages) and {G_ST was calculated for all possible subsets of the varieties. The three old varieties comprised the densest cluster and were also more genetically diverse than two of the three new varieties. Varieties with clear changes among CO₂ levels were rather genetically diverse. Thus, the varieties represent different traits, which could be exploited in future breeding of oilseed rape.