Investigating the regrowth of wild barley (Hordeum spontaneum Koch.) and feral rye (Secale cereale L.) weeds compared to wheat after freezing stress

Knowledge of freezing stress tolerance in wild barley and feral rye as the most important weeds in wheat fields can be used to predict their geographical distribution and management plannings. To this end, an experiment was conducted in Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran, in autumn 2017. Two wheat genotypes (cultivar Pishgam and Iranian landrace Ghezel Khoushe) and two weeds (wild barley and feral rye) were grown up to two to four true leaves stage under natural conditions and then exposed to a temperature range of +4 to -20 °C (+4 oC as control and 0, -4, -8, -12, -16 and -20 oC as freezing temperatures). The results showed that reducing temperature from -8 to -12 °C led to a 36% decrease in survival of wild barley, while the survival of wheat (Pishgam and Ghezel Khoushe) and feral rye was 100%. Wild barley had the highest lethal temperature reducing 50% of survival (LT50su = -12.8 °C) and temperature rducing 50% of leaf area (RLAT50 = -11.2 °C). Among the studied plant species, wheat (landrace Ghezel Khoushe) and feral rye with -11.8 °C and -11.6 °C, respectively, had the lowest temperature rducing 50% of shoot dry weight (RSDWT50), while the wild barley with -8.1 °C had the highest RSDWT50. The highest and lowest chlorophyll content (SPAD) among the living plants were observed at +4 and -12 °C, respectively, and  feral rye with 19.5 and wild barley with 10.3 SPAD unit showed the highest and lowest chlorophyll content, respectively. The results of this study showed that high tolerance of feral rye to freezing stress is probably one of the main reasons for its widespread distribution in winter wheat fields. Therefore, it is necessary to predict dispersion and possible invasion and consequently appropriate strategies to manage this weed in areas with cold climates.