The present work investigates the laminar-turbulent transition of the flow around a typical section of a wind turbine blade under different levels of isotropic inflow turbulence at a Reynolds number of Rec = 10^5 . Wall-resolved large-eddy simulations are performed under different turbulence intensities (TI) up to TI = 2.8 %. The results are analyzed with tools based on the linear stability and optimal-perturbation theory. At TI = 0%, transition to turbulence via the breakdown of Kelvin-Helmholtz (KH) rolls formed over the laminar separation bubble (LSB) is seen. These modes start to grow upstream of the LSB as an inflectional instability. At TI = 1.4 % rolls are also seen; but, instabilities formed by the interaction between streaks and the LSB also contribute to transition. The streaks are estimated to have a spanwise wavenumber around β = 100 ( β δ = 0.19 at 20 % chord; δ is the displacement thickness) and a frequency in the range f = 5 − 8 (f δ ∗ /ue = (1.4 − 2.3) × 10^−2 at 40 % chord; ue is the boundary layer edge velocity), close to that of the shear-layer instability. In the T I = 2.8 % case, the flow is heavily influenced by the presence of streaks, which stabilize the flow concerning inflectional/KH instabilities, but, at the same time, undergoes varicose-type instabilities and breakdown to turbulence.