6533b7d7fe1ef96bd1267701

RESEARCH PRODUCT

Papaver rhoeas plants with multiple resistance to synthetic auxins and ALS inhibitors

subject

description

The pattern of resistance to synthetic auxins and ALS inhibitors was investigated in a population of corn poppy (Papaver rhoeas), originating from central Greece. In June 2013 seed capsules and leaf fragments were collected from ten P. rhoeas plants that survived 2,4-D application in a wheat field with an history of ALS-inhibiting herbicide application. The material was collected separately for each plant. DNA from the collected leaf fragments of each plant was subjected to ALS genotyping at codons 197 and 574 using dCAPS assays. The collected seeds were treated with gibberellic acid to break dormancy and each progeny was planted separately in plastic modular trays containing potting soil. Seeds from a reference sensitive population were also sown simultaneously. After emergence, plants were thinned to one per module and the trays were placed in a glasshouse (15-25°C, natural photoperiod, during December 2013). Plants of the studied population were sprayed at the 5-6 true leaf-stage with 2,4-D (ester form) at 0.25, 0.5, 1, 2, 4 and 8 times the recommended field-rate (600 g a.e./ha). The sensitive reference population plants were sprayed with the same herbicide at 0.0625, 0.125, 0.25, 0.5, 1 and 2 times the recommended field-rate. Water-sprayed control plants were also included for each population. A total of 508 progeny plants and 41 reference population plants were tested. Of these, 436 progeny plants and 36 reference population plants were sprayed with an herbicide rate (>0). Visual assessment of survival and measurement of plant dry weights in all treatments took place twelve weeks after herbicide application. ED50 values were calculated for each progeny and for the sensitive population, using the log-logistic four parameter model of the R software (drc tool). The dCAPS assays showed that nine out of the ten mother plants collected in the field, carried a mutation at codon Pro197. Of these nine plants, three were homozygous mutants. No mutation was identified at the ALS codon Trp574. Target-site mutation of the ALS gene, and most commonly to the Pro197 codon, is considered the dominant mechanism of resistance to ALS inhibitors in P. rhoeas. In the dose-response experiment, survival of the progeny plants at the recommended field-rate was 82%, while at 4 times the recommended field-rate (2400 g a.e./ha) it was 27%. Four plants from four distinct progenies survived the highest 2,4-D rate applied (4800 g a.e./ha). All reference population plants were killed at rates higher than 0.25 times the recommended field-rate. The ED50 values calculated were 37 g a.e./ha for the reference population and more than 1300 g a.e./ha for the progeny of the plants from the studied population. ALS resistance in P. rhoeas is both widespread and well documented. Resistance of this species to synthetic auxins is also known to occur, albeit it currently appears less widespread and common. This work is the first demonstration of the occurrence of multiple resistance to both synthetic auxins and ALS inhibitors in the same P. rhoeas plants, raising concerns for the control strategy of such genotypes.