Nikolaos S. Kaloumenos

Corn poppy (Papaver rhoeas) cross-resistance to ALS-inhibiting herbicides.

BACKGROUND Papaver rhoeas (L.) has evolved resistance to tribenuron in winter wheat fields in northern Greece owing to multiple Pro(197) substitutions. Therefore, the cross-resistance pattern to other sulfonylurea and non-sulfonylurea ALS-inhibiting herbicides of the tribenuron resistant (R) and susceptible (S) corn poppy populations was studied by using whole-plant trials and in vitro ALS catalytic activity assays. RESULTS The whole-plant trials revealed that tribenuron R populations were also cross-resistant to sulfonylureas mesosulfuron + iodosulfuron, chlorsulfuron and triasulfuron. The whole-plant resistance factors (RFs) calculated for pyrithiobac, imazamox and florasulam ranged from 12.4 to > 88, from 1.5 to 28.3 and from 5.6 to 25.4, respectively, and were lower than the respective tribenuron RF values (137 to > 2400). The ALS activity assay showed higher resistance of the ALS enzyme to sulfonylurea herbicides (tribenuron > chlorsulfuron) and lower resistance to non-sulfonylurea ALS-inhibiting herbicides (pyrithiobac > florasulam ≈ imazamox). CONCLUSION These findings indicate that Pro(197) substitution by Ala, Ser, Arg or Thr in corn poppy results in a less sensitive ALS enzyme to sulfonylurea herbicides than to other ALS-inhibiting herbicides. The continued use of sulfonylurea herbicides led to cross-resistance to all ALS-inhibiting herbicides, making their use impossible in corn poppy resistance management programmes.

Multiple Pro197 Substitutions in the Acetolactate Synthase of Corn Poppy (Papaver rhoeas) Confer Resistance to Tribenuron

Abstract Variations in the acetolactate synthase (ALS) gene sequence were determined from 28 populations of corn poppy resistant (R) to tribenuron and from 6 populations susceptible (S) to this herbicide. The ALS gene fragment (634 bp) sequence revealed in R populations five point mutations at the codon Pro197, and among them the substitution of Pro197 by Ala was the most common. The sequencing chromatograms revealed that nine R individuals had only the mutant ALS gene and were homozygous (RR), 18 R individuals had both the wild type and the mutant ALS gene and were heterozygous (RS), whereas one R individual was heterozygous but with two different mutant ALS alleles (R1R2). The use of restriction digestion profile analysis to verify the DNA sequence results by detecting the existence of point mutations at the codon 197 managed to distinguish the R and S alleles and confirmed the results obtained from the sequencing chromatograms analysis. The secondary protein structure prediction suggested the formation of novel β-strands for each of the five mentioned amino acid substitutions that was not present in wild type ALS around the mutant site. These findings support the hypothesis that the substitution of Pro197 by Ser, Thr, Ala, Arg, or Leu resulted in altered secondary structure, which stabilizes an ALS tertiary conformation that prevents tribenuron binding and thus confers resistance to this herbicide. Nomenclature: Tribenuron; corn poppy, Papaver rhoeas L. PAPRH.

Identification of a Johnsongrass (Sorghum halepense) Biotype Resistant to ACCase-Inhibiting Herbicides in Northern Greece

Abstract A johnsongrass population from a cotton field in northern Greece along with a population from the university farm (“Control”) were evaluated for resistance to the herbicide quizalofop; cross-resistance to cycloxydim, propaquizafop, and fluazifop (acetyl coenzyme A [CoA] carboxylase [ACCase]-inhibiting herbicides), and multiple resistance to nicosulfuron (acetolactate synthase [ALS]-inhibiting herbicides). In greenhouse experiments, the application of four times the recommended rates of quizalofop and propaquizafop to suspected resistant rhizomatous plants resulted in 4 and 5% growth reduction, respectively. However, the growth of suspected resistant seedlings was reduced by 54 and 28% after the application of two times the recommended rate of the same herbicides. In contrast, the application of quizalofop and propaquizafop at recommended rates on rhizomatous plants and seedlings of the Control population reduced their growth by 97 to 100%. Also, the growth reduction of both populations by the application of cycloxydim, fluazifop, and nicosulfuron at recommended rates ranged from 93 to 100%. In the field experiment, quizalofop and propaquizafop applied at four times the recommended rate reduced growth of the suspected resistant population by 9 and 18%, respectively, whereas the recommended rate of fluazifop gave a 94% growth reduction of this weed. The herbicide rate required for 50% growth reduction (GR50) values for rhizomatous plants of the suspected resistant population were 0.90 and 2.465 kg ai/ha for quizalofop and propaquizafop, respectively, whereas the corresponding GR50 values for the seedlings were 0.074 and 0.185 kg ai/ha. These results indicate that a johnsongrass population developed cross-resistance to quizalofop and propaquizafop, but did not evolve cross-resistance to cycloxydim and fluazifop or multiple resistance to nicosulfuron. Nomenclature: Cycloxydim; fluazifop; nicosulfuron; propaquizafop; quizalofop; johnsongrass, Sorghum halepense (L.) Pers. SORHA; cotton, Gossypium hirsutum L.

Corn Poppy (Papaver rhoeas) Resistance to ALS-Inhibiting Herbicides and its Impact on Growth Rate

Abstract Fifty corn poppy populations originating from three counties of northern Greece were evaluated for resistance to tribenuron. Twelve of the populations (six sampled from cereal fields and six from margins) were sampled from the county of Thessaloniki, 15 (13 sampled from wheat fields and two from margins) from Kilkis, and 23 (21 sampled from cereal fields and two from margins) from Serres. Fifty, 39, and 95% of the populations sampled from winter wheat fields originating from Thessaloniki, Kilkis, and Serres were resistant (R), respectively. However, all populations sampled from margins of the same areas were susceptible (S). All populations examined were susceptible to 2,4-D and bromoxynil. The level of resistance to tribenuron varied among populations with the herbicide dose required to reduce growth by 50% (GR50) ranging from 41 g ha−1 (R/S, resistance ratio 137) for the least resistant to over 720 g ha−1 (R/S greater than 2,400) for the most resistant populations. Fresh weight accumulation, seed production, and capsule number of eight R populations grown under field conditions were similar to those recorded for eight S populations originating from sites with high proximity of their respective R populations. However, the estimated mean growth rate (MGR) indicated significant differences due to the resistance trait and the populations origin. In particular, the R populations that originating from Thessaloniki and Serres had MGR 1.3 to 4.3 times lower than the respective S populations, whereas the R populations from Kilkis had similar or higher MGR values compared to the respective S populations. The populations with the highest R/S (greater than 2,400) had low MGR values, and the populations with R/S ranging from 1,437 to 2,227 had high MGR values. Nomenclature: Bromoxynil; tribenuron; corn poppy, Papaver rhoeas L. PAPRH.

Influence of Pyrithiobac Application Rate and Timing on Weed Control and Cotton Yield in Greece1

Field experiments were conducted at four locations (Larissa, Halkidona, Thessaloniki, and Halastra) in Greece to evaluate weed and cotton response to various pyrithiobac rates applied preplant incorporated (PPI), preemergence (PRE), or postemergence (POST). Pyrithiobac applied PPI or PRE at 0.068, 0.102, or 0.136 kg ai/ha controlled black nightshade, pigweeds, and common purslane at Larissa. However, pyrithiobac applied PRE at Thessaloniki and Halkidona was more effective against black nightshade and pigweeds than pyrithiobac applied PPI. Pyrithiobac applied PPI or PRE at 0.068 or 0.102 kg/ha did not control common lambsquarters at Thessaloniki. Weed control with trifluralin plus fluometuron applied PPI and alachlor plus fluometuron applied PRE at Larissa was slightly lower than that obtained with pyrithiobac. At Halkidona, trifluralin plus fluometuron applied PPI and alachlor plus fluometuron applied PRE provided weed control similar to that obtained with pyrithiobac. But at Thessaloniki, these treatments provided better weed control than pyrithiobac. Furthermore, pyrithiobac applied early postemergence (EPOST), midpostemergence, or in sequential systems controlled black nightshade and pigweeds, but it resulted in fair to good control of common purslane, velvetleaf, and common cocklebur. None of the POST treatments controlled common lambsquarters. Fluometuron EPOST controlled black nightshade, common lambsquarters, and common purslane ≥70, 86, and 67%, respectively. Fluometuron EPOST did not control pigweeds, velvetleaf, and common cocklebur. Cotton treated with pyrithiobac, regardless of method of application, yielded similar to the weed-free control. Cotton treated with pyrithiobac PPI at the highest rate (0.136 kg/ ha) yielded less at Halkidona, although adverse effects after its application were not visually apparent. Yield of cotton treated with herbicides was similar, with no difference among treatments. Nomenclature: Alachlor; fluometuron; pyrithiobac; trifluralin; black nightshade, Solanum nigrum L. #3 SOLNI; common cocklebur, Xanthium strumarium L. # XANST; common lambsquarters, Chenopodium album L. # CHEAL; common purslane, Portulaca oleracea L. # POROL; prostrate pigweed, Amaranthus blitoides S. Wats AMABL; redroot pigweed, Amaranthus retroflexus L. # AMARE; velvetleaf, Abutilon theophrasti Medicus # ABUTH; cotton, Gossypium hirsutum L. ‘Stoneville 474’, ‘Hazera Vered’, ‘Deltapine 20’, ‘Deltapine 50’, ‘Stoneville Bravo’. Additional index words: Application timing, cotton herbicide, crop injury, residual activity. Abbreviations: EPOST, early postemergence; MPOST, midpostemergence; MSMA, monosodium salt of methylarsonic acid; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; WAP, weeks after planting; WAT, weeks after treatment.

First report of a “Candidatus Phytoplasma solani” related strain associated with a disease of Datura stramonium in Greece

Jimsonweed (Datura stramonium), family Solanaceae, a common weed in spring crops in Greece, includes two botanical varieties (var. stramonium and var. tatula). During a field trial at the Aristotle University Farm (40o32N’ 22o59’E, 6 m asl), in which four accessions of D. stramonium were tested for growth rate and alkaloid content, phytoplasma-like symptoms were observed. Initially, the affected plants showed interveinal chlorosis of the upper leaves, stunting and flower malformation, whereas at maturity they did not form normal fruits and developed leaf necrosis. To investigate the possibility of a phytoplasma infection, DNA was extracted from leaf samples of symptomatic and apparently healthy plants of both varieties according to Psifidi et al. (2010). A nested PCR was performed using two universal primer sets specific to the phytoplasma 16S rRNA gene: P1/P7 (Schneider et al., 1995) followed by R16F2n/R16R2 (Gundersen and Lee, 1996). The expected ca. 1,200 bp product, amplified esclusively from symptomatic plants of both varieties, was cloned and sequenced. BLAST analysis revealed 99% similarity with sequence AF248959 of stolbur phytoplasma (16SrXII group, Ca. Phytoplasma solani). Sequences from both varieties were identical, indicating infection by the same phytoplasma strain and were deposited in EMBL-EBI (accession Nos HE598778 and HE598779). Diseased plants of var. tatula and stramonium showed 49-69% and 38% reduction of the above-ground fresh weight, respectively, compared to healthy plants, hence making the phytoplasma an important pathogen of jimsonweed, which constitutes a reservoir plant in the field. This is, to our knowledge, the first report of a Ca. Phytoplasma solani-related disease in jimsonweed in Greece.

Activity, adsorption, mobility, and field persistence of pyrithiobac in three soils

Abstract Petri dish bioassays, based on root response of corn grown in soil and perlite, were used to study the activity, adsorption, and leaching of pyrithiobac in a clay, loam, and a clay loam soils containing 2.3, 1.4, and 1.3% organic matter, respectively. Both bioassays indicated that activity of pyrithiobac (reduction of corn root length) increased with increasing herbicide concentration, but in a nonlinear manner, particularly at higher concentrations. Activity of pyrithiobac was similar in clay loam and loam soils, but was lower in clay soil. Adsorption distribution coefficients (Kd) for the clay, loam, and clay loam soils were 0.56, 0.10, and 0.24, respectively. Pyrithiobac leached through all three soils, and biologically available herbicide was detected below 30 cm in all soils; however, the amount leached through the clay soil was lower than that leached through the other two soils. Field persistence of pyrithiobac applied preplant incorporated (PPI), preemergence (PRE), or postemergence (POST) at 68, 102, or 136 g ha−1 was similar in loam and clay loam soils, but was more persistent in clay soil. Pyrithiobac applied POST in clay and loam soils was more persistent than that applied PPI or PRE; however, in clay soil field persistence of POST pyrithiobac was similar with that applied PPI or PRE. Biologically available residues were not detected in 0- to 10-cm soil depth 120 d after any herbicide treatment applied either PPI or PRE in all soils, but this was not the case for pyrithiobac applied POST in the loam soil. Adsorption of pyrithiobac was very low in all three soils, and this was the reason for its increased mobility even below 30-cm depth in all soils. The field persistence of pyrithiobac was generally less than one growing season. However, some pyrithiobac may have moved deeper in the soil and could be harmful to rotational crops after plowing or through capillary movement upward. Nomenclature: Pyrithiobac; corn, Zea mays L. ‘Pioneer Costanza’; cotton, Gossypium hirsutum L. ‘Stoneville 474’, ‘Hazera Vered’, ‘Deltapine Vulcano’.

In the wild hybridization of annual Datura species as unveiled by morphological and molecular comparisons

BackgroundThe present work aimed to verify whether intermediate variants were natural crosses between Datura species (D. stramonium forms and D. ferox). Their existence has been long ago insinuated but has not been studied using morphological features and molecular tools. The variants differed in stem coloring, upper bearing forks, and fruit characters.ResultsPrincipal Components Analysis of 11 morphological characteristics showed that D. ferox and D. stramonium (forms stramonium and tatula) were quite different and the putative hybrids were intermittent. The D. ferox × D. stramonium f. tatula was closer to the latter of its parents. Sequencing analysis revealed identical amplified trnL intron in all variants and a 100% homology with D. stramonium accession number EU580984.1 suggested that this plastid cannot discern Datura variants. However, genomic analysis with URP markers indicated that the hybrids had >60% genetic makeup similarity with both parents suggesting that the intermediate variants were putative inter-specific hybrids. Moreover, the dendrogram stemmed from cluster analysis of the fingerprint profile of variants placed D. stramonium and D. ferox in different branches indicating their genetic differentiation from each other as well as from their hybrids.ConclusionsThe findings suggest that the natural hybridization of annual Datura species occurs. Extrapolating, this hybridization could be the first step for speciation. More possibly, it can alter population composition, its weediness and adaptability to local conditions.