Chromatic index, treewidth and maximum degree

We conjecture that any graph $G$ with treewidth~$k$ and maximum degree $\Delta(G)\geq k + \sqrt{k}$ satisfies $\chi'(G)=\Delta(G)$. In support of the conjecture we prove its fractional version. We also show that any graph $G$ with treewidth~$k\geq 4$ and maximum degree $2k-1$ satisfies $\chi'(G)=\Delta(G)$, improving an old result of Vizing.Comment: 14 pages, 3 figures, minor changes, accepted for publication in Electronic Journal of Combinatoric