TP content could explain partially the auto-toxic potential of barley, leaving the eventuality of other allelochemicals to be implicated in. Auto-toxic potential was not stable over time, indicating that is not highly genetically controlled. In fact, a relatively dry 00/01 GS, characterized by the highest concentrations of phenolic acids in BP tissues, was the sole GS that showed a significant relationship (r = 0.42, p < 0.10) between RG inhibition and TP and at the same time (r = 0.46, p < 0.8) between CL/RL ratio and TP, though the probability level in both cases was relatively high. Three phenolic acids (POH, SYR, PCO) were found to be involved significantly in the expression of barley auto-toxicity. The most present phenolic acid (VAN) in barley plant tissue did not show an individual significant role in barley auto-toxicity, suggesting rather a synergetic effect with one or more implicated phenolic acids. Also, the less frequent phenolic acid (FER) was the sole involved with CL/RL ratio, suggesting that its effect is a differential allocation of dry matter in favor of barley shoot growth. ‘Rihane’ was the sole barley variety of which TP content was significantly correlated to barley auto-toxicity27/11/2014TP content could explain partially the auto-toxic potential of barley, leaving the eventuality of other allelochemicals to be implicated in. Auto-toxic potential was not stable over time, indicating that is not highly genetically controlled. In fact, a relatively dry 00/01 GS, characterized by the highest concentrations of phenolic acids in BP tissues, was the sole GS that showed a significant relationship (r = 0.42, p < 0.10) between RG inhibition and TP and at the same time (r = 0.46, p < 0.8) between CL/RL ratio and TP, though the probability level in both cases was relatively high.