  A non-perturbative method of Field Correlators is applied to calculate the
Polyakov loop dependence on temperature, $L(T)$, in the 2+1 flavor QCD with
small quark masses, so the only relevant scale is the color-electric string
tension $\sigma(T)$. Polyakov loop in the temperature range 100 MeV $\lesssim
T\lesssim$ 400 MeV is expressed via the heavy-light meson mass that decreases
with $T$ as $\sqrt{\sigma (T)}$. The latter is deduced from a gradually
vanishing chiral condensate. The resulting $L(T)$ is in good agreement with
recent lattice data.
