Importance of the P106S Target-Site Mutation in Conferring Resistance to Glyphosate in a Goosegrass (Eleusine indica) Population from the Philippines

Abstract

Few studies on herbicide resistance report data to establish unambiguously the correlation between genotype and phenotype. Here we report on the importance of the EPSPS prolyl106point mutation to serine (P106S) in conferring resistance to glyphosate in a goosegrass population from Davao, Mindanao Island, the Philippines (Davao). Initial rate-response studies showed clear survivors within the Davao population at glyphosate rates that completely controlled the standard sensitive goosegrass population (STD1). Assessment of potential resistance mechanisms identified the presence of P106S mutant individuals in the Davao population. Polymerase chain reaction (PCR) amplification of specific alleles (PASA) analysis established that the mixed-resistant Davao population was comprised of 39.1% homozygous proline wild-type (PP106), 3.3% heterozygous serine mutant (PS106), and 57.6% homozygous serine mutant (SS106) genotypes. Further rate-response studies on plants with a predetermined genotype estimated the Davao SS106 individuals to be approximately 2-fold more resistant to glyphosate compared to Davao PP106 individuals. Extensive analysis at different goosegrass growth stages and glyphosate rates established strong correlation (P < 0.001) between presence of P106S in EPSPS and the resistant phenotype. Importantly, no differences in the pattern of absorbed or translocated14C–glyphosate were observed between PP106 and SS106 Davao genotypes or Davao and STD1 individuals, suggesting that glyphosate resistance in the Davao population was attributable to an altered target site mechanism. This study demonstrates that whilst P106S in EPSPS confers a moderate resistance level to glyphosate, the mechanism is sufficient to endow glyphosate failure at the recommended field rates.

Glyphosate influence on the physiological parameters of Conyza bonariensis biotypes

“…In the Lolium rigidum population, the substitution of proline for threonine confers a resistance level of up to 3.4 times (Wakelin & Preston, 2006). In Eleusine indica, another species that is resistant to changes in EPSPs, the same substitutions occurring in Lolium multiflorum (proline for alanine) confer low levels of resistance (Kaundun et al 2008). Still, Carvalho et al (2012) found two amino acid substitutions at positions 182 and 310 of the EPSPS gene that may contribute to resistance to glyphosate, changing proline for threonine and tyrosine for cysteine, respectively.…”

A Modified phosphate-carrier protein theory is proposed as a non-target site mechanism For glyphosate resistance in weeds

“…ELEIN biotypes from the Philippines also were found to have the P 106 S mutation which gave a resistance factor of 2.8 (Kaundun et al, 2008). The resistance factor associated with the P 106 T mutation was found to be 3.4 in resistant biotypes of Lolium rigidum from Australia (Wakelin & Preston, 2006).…”

Goosegrass Resistant to Glyphosate in Brazil

“…Thereafter, resistant populations were found in different continents around the world (Yuan et al, 2005;Kaundun et al, 2008;Mueller et al, 2011;Molin et al, 2013;Heap, 2016). In addition to the resistance to glyphosate, some populations of goosegrass may have resistance up to four mechanisms of action simultaneously (EPSPS, ACCase, Photosystem I and GS-GOGAT) (Jalaludin et al, 2014).…”

“…The resistance mechanism to glyphosate in other countries' goosegrass involves replacement of a proline by serine or threonine at position 106 in the EPSPS gene (P106S or P106T) (Baerson et al, 2002;Ng et al2004;Yu et al2007;Kaundun et al, 2008Kaundun et al, , 2011, or the EPSPS gene amplification in resistant plants (Chen et al, 2015). Such single mutation confers intermediate levels of glyphosate resistance (RF = 2 to 4).…”