\documentclass[12pt]{article}
\usepackage[utf8]{inputenc}
\usepackage[greek,english]{babel}
\usepackage{alphabeta}


\usepackage{newtxtext}
\usepackage{substitutefont}
\substitutefont{LGR}{\rmdefault}{txr}
\usepackage{multirow}

\begin{document}
\section*{πίνακας}
\begin{table}[h]
	\begin{tabular}{|c|c|c|c|c|}
	\hline
	\multirow{2}{*}{κατάσταση} & \multicolumn{4}{c|}{PT} \\
		\cline{2-5}
	& $S_1$ & $S_2$ & $S_3$ & $S_4$ \\
	\hline
	\multirow{2}{*}{MR1} & 0.1 & \multirow{2}{*} {0.7}
        &	0.2 & 0.3 \\ 
        \cline{2-2} 
        \cline{5-5}
	& 0.1 & & &  0.2 \\
	\hline

	\end{tabular}
	\caption{My Caption} \label{tbl:1}
\end{table}
\end{document}

