The Genotypic Distribution and Molecular Bases ALS-Inhibiting Herbicides Resistant Lolium Populations in Wheat Fields in Saudi Arabia

During the last decade, several resistances to specific grass weed herbicides appeared within grass weeds growing in winter cereals.  Italian ryegrass (Lolium multiflorum Lam) is one of the most common weed species in winter cereals in Saudi Arabia. Herbicide resistance has been growing since the mid 90’s and exclusive herbicide use is not enough in many cases, so that it is necessary to combine as many control tools as possible. The molecular biology techniques demonstrated that two resistance mechanisms can be found in the same plant (target site mutation and herbicide detoxication). The present study aimed to identify and describe the distribution of mutations conferring resistance to ALS herbicides in wild Italian ryegrass populations invading wheat fields in Saudi Arabia using biotechnology. Seeds of wild Italian ryegrass populations were collected from several isolated fields within seven wheat producing areas in Saudi Arabia during March to June, 2010.  In addition, a susceptible population was obtained as control population. The collected populations were subjected to molecular screening using specific primers (6 primers) published as specific for detection resistant and tolerant to herbicides. Screening for ALS resistance was studied on fifty randomly selected plants from each of the eight populations. In a greenhouse study, the populations were also subjected to two doses  of  a commercial brand of  the ALS herbicide Mesosulfuron-methyle  (100 mg a.i/ha and 200 mg a.i/ha). Result showed significant differences among populations in response to the herbicide treatments. All populations showed some level of resistance in response to the low herbicide dose and some survival with the high dose indicating the present of resistant mutants in all lolium populations. Results of molecular screening for ALS resistance indicated the present of resistance genes in all regions. The genomic sequences were determined directly from the amplified PCR fragments. Comparing the known ALS cDNA with our sequence revealed six mutants of base pair substitutions. Two mutants of six mutants were of a particular importance where the amino acid substitution led to a change in charge and polarity of the resultant amino acids. M4 and M5 were found to be a potential new identified mutants in ALS gene in resistant lolium populations grown in the kingdom.