Study the Indicators of Germination and Growth of Some Species of Weeds under Different Thermal Conditions.

Germination of seeds is affected by many internal and external factors. The main external factors affecting seed's germination are oxygen, water, light, and temperature (Manoto et al., 2004). The temperature is one of the most important external factors that effect on seed's germination. Whereas, at low temperatures, the germination rate decreases, and with rising temperatures, this rate increases until it reaches the optimum level, but with the high temperature above this limit, the germination rate decreases as a result of the damage in the seeds (Fu et al., 2017). The appropriate temperature for most seeds to germinate is between 15 and 30 ‏°C. The effect of temperature depends on several factors, including the species, varieties, growth areas, seed's quality, and the period after the harvest (Shaban, 2013). It was noted that there was no germination of P. oleracea seeds at temperature 5 C° and the germination rate was very low at temperature 10 C° and the best temperature for germination was at 30 C°( Ustuner, 2002). A study conducted on the seeds of P. oleracea to determine the influence of temperatures on seed's germination in the lab conditions reported that the germination percentage in the dark/dark system was 81% at (25/15°C), while in the light/dark system, the germination was 70% at (25/15°C) ( Chauhan and Johnson, 2009). In other study to determine the effect of temperatures on seed germination in A. retroflexus, the results showed that the minimum temperature for seed germination was > 5 C; maximum germination occurred between 35 and 40 C (Ghorbani et al, 2017). The effects of temperature on seed's germination of nine Amaranthus species were tested under constant and rotating temperature regimens at 5, 10, 15, 20, 25, 30, and 35° C. It has been reported that the constant and rotating temperatures regimens increased total germination of all Amaranthus species (Lawrence et al, 2004). A search was conducted to assess the influence of temperature on seed germination of E. immaculate. Where it was found that seeds germinated over a constant temperature estimated of 25 to 45°C with a 14-h photoperiod and at 30 to 50°C in continuous darkness with higher germination value reached 80% (Rayhaneh et al, 2015). In laboratory conditions, Abstract: The aim of this study is to determine the effect of temperature on the germination and growth indices of some species of weeds in laboratory conditions. The tested species were Amaranthusretroflexus L., Amaranthusblitoides S., Euphorbia maculata L., Portulacaoleracea L. and CuscutacampestrisYunck. To achieve this goal, the germination rate (GR), speed of germination (SG), Mean germination time (MGT), and the daily growth rate of seedlings (DGR) were calculated. The results showed that increasing temperatures to 35 ° C increases the value of the studied indicators. There was no significant difference between thermal treatments for A. retroflexus, the percentage of germination in all treatment was high, but there was a significant difference in other indicators. There was no germination of the species E. maculata, P. oleracea and C. campestris at 17 ° C during the trial period. The germination rate increased with increasing temperature. E. maculata was the most tested species affected by low temperature. The results of this study confirm the role of temperature in the beginning of the emergence and speed of development of the weed population, especially that some species show great response to thermal differences.