Abstract :
In order to evaluate the relative fitness of clodinafop propargyl-resistant and –susceptible ryegrass (Lolium rigidum) biotypes, under temperature and light regimes, experiments were carried out as a factorial randomized complete block design with four replications. The treatments were consisted of ryegrass biotypes (susceptible, semi- resistant and resistant), constant temperatures (5, 10, 15, 20, 25° C) and different regimes of light (14 d dark, 14/12 h dark/light and 7/7 d dark/light). Results indicated that the germination percentage of ryegrass susceptible biotype was improved with increasing the temperature by 20 ° C and then to be fixed at 25 ° C. In contrast, the germination percentage of two other ryegrass accessions was increased up to 15 ° C and then dropped. Under the maximum temperature (25° C), the germination percentage of semi-resistant (semi-R) and Resistant (R) accessions was less than that of susceptible accession. Overall, the germination percentage of all ryegrass accessions increased as temperature increased. The effect of different regimes of light showed that the germination percentage of three accessions was greater in semi-darkness regime than two other treatments. There was significant difference in the percent germination of the three biotypes in absolute darkness, and the R population achieved the highest germination percentage, followed by semi –R and susceptible accessions. Under normal conditions, significant difference was found among the accessions and the maximum germination percentage was produced in semi –R population, followed by susceptible and resistant populations.
