Abdullah A. Al-Doss, Abdelhalim I. Ghazy, Sulieman A. Al-Faifi, Hussein M. Migdadi, Muhammad A. Khan, Megahed H. Ammar and Mohammad I. Althamrah
Collage of Food and Agriculture, Riyadh, KSA
Annual ryegrass is one of the most common weed species in Saudi wheat fields. Resistance to ALS herbicides has evolved widely in Saudi Arabia, however, no earlier attempt has been dedicated to elucidate or identify mutations conferring resistance in annual ryegrass populations (Lolium rigidum) invading wheat fields in this region. Six reported ALS-linked primers were used to identify potential ALS-herbicides resistant alleles of seven L. rigidum populations collected from wheat fields across Saudi Arabia in addition to international sensitive accession. Molecular screening revealed no apparent polymorphism among or within populations. Therefore, genomic sequences were determined from cloned amplified PCR fragments. Sequence alignment of ALS cDNA sequence in public domain with our sequences revealed ten base pair substitutions. Five of those mutants had a potential phenotype alteration since they led to amino acid change. The Pro-197-Thr in Tabouk and Pro-197-Gln in Harad populations occurred at same position reported earlier, with a novel amino acid change, threonine (Thr) that was not reported. Other mutant Lys-98-Met represents potential new ALS-allele, with amino acid methionine detected in all Saudi populations except the resistant population (Tabouk), where it was Lysine. One more potential allele was detected in Asp-185-Tyr, where it was Aspartic acid in known resistant allele as well as in all Saudi populations except in Tabouk, the resistant population, where it converted to Tyrosine. These two potential alleles are of a particular interest and needs further confirmatory studies. Other mutant, Glu-105-Gly may represent ecotype-specific mutant; it showed consistent amino acid change among all Saudi populations regardless their resistance level. These mutants may be utilized as ecotype specific mutants that differentiate Saudi from other annual ryegrass populations. Furthermore, Glu-213-Lys and Ile-462-Thr mutants occurred only once each in international sensitive check, and Wadi El-Dawaser Population, respectively. The obtained sequences were deposited to NCBI gene bank through individual submission (KM000067, KM000068 and KJ953895). Results obtained in this study will help to implement new strategies for annual ryegrass weed management.
Keywords: Herbicide resistance, annual ryegrass, point mutation, base pair substitution.