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Amino acid substitutions that confer herbicide-resistance may cause fitness costs in mutant plants at unfavorable levels in contrast to wild-species. The fitness costs in three Lolium rigidum populations (AH3 (Ile-2041-Asn) and BO2 (Ile-1781-Leu) as resistant (R) to clodinafop-propargyl, an ACCase (acetyl-CoAcarboxylase) inhibitor, carrying the mutations 1781 and 2041, respectively, and HF as susceptible (S)) were studied during 2014 and 2016. The germination rates and percentages of the three L. rigidum populations, and competition between them and Triticum aestivum using substitution series experiments were assessed. The BO2 and AH3 populations showed resistance to clodinafop-propargyl due to mutations in their ACCase genes. The germination rate for L. rigidum decreased as the sowing depth increased, with the lowest germination rate being found at 8 cm. AH3 and HF populations presented higher seed germination under water and NaCl salinity stress, but no fitness cost variations were observed among these R populations under optimal growth conditions. Diverse germination responses to light conditions were observed between the S and R L. rigidum populations. The highest germination percentage was observed in the HF population at the two-week lighting + two-week darkness regime. The comparison of relative yield total and relative crowding coefficient showed that T. aestivum was more competitive than L. rigidum. However, among ACCase-resistant L. rigidum populations, AH3 population was the most competitive presenting no fitness costs. This R population was more competitive than the S (HF) one under competitive conditions. These results show that fitness costs in the R L. rigidum populations vary according to the specific mutation at the ACCase gene that confers resistance to clodinafop-propargyl. In conclusion, mutations occurring at the 2041 position in the ACCase gene caused fitness costs, but those occurring at the 1781 position did not generate fitness costs for L. rigidum. Therefore, non-chemical methods should be considered unfavorable for resistant populations of this species. [ABSTRACT FROM AUTHOR]

Repeated applications of the same herbicide(s), which are characterized by the same mode of action, increase selection pressure, which in turn favours the evolution of herbicide-resistant weeds. Glufosinate is a broad-spectrum non-selective herbicide being used for weed control for many years around the world. Rigid ryegrass (Lolium rigidum Gaud.) is an economically important grass weed in Greece. Recent complaints by growers about control failure of rigid ryegrass with glufosinate require further investigation and have been the basis of this study. The objectives of this study were to confirm the existence of glufosinate-resistant L. rigidum in Greece and evaluate the effect of L. rigidum growth stage on glufosinate efficacy. Twenty populations of rigid ryegrass from Greece were sampled from five regions, and whole plant dose-response studies were conducted for five populations under controlled conditions with eight rates of glufosinate (0.0, 0.098, 0.187, 0.375, 0.75, 1.5, 3.0, and 6.0 kg a.i. ha-1). Glufosinate resistance was confirmed in three out of five populations with the level of resistance ranging from three-to seven-fold compared with the susceptible populations based on above-ground biomass reduction. Results also revealed that the level of glufosinate-resistance of rigid ryegrass was dependent on the growth stage at which it was applied. [ABSTRACT FROM AUTHOR]

A field experiment was conducted to evaluate the effects of several cover crops against a serious invasive weed, Conyza albida. The particular species is characterized by a wide dispersal, an enormous seed production and a high trend for glyphosate-resistance development. In the present study, four different cover crops were tested, namely Lolium multiflorum, L. perenne, Festuca arundinacea and Trifolium repens. The experiment was performed as a randomized complete design and several measurements on soil coverage and weed growth and density were taken. Soil coverage was faster and higher for L. multiflorum, followed by F. arundinacea and T. repens. On the contrary, canopy development for the perennial L. perenne was 62-72% lower than the other cover crops. This rapid and high canopy development especially of L. multiflorum and T. repens resulted to the significant reduction of C. albida density (lower by 87 and 83%, respectively) and also to weeds' growth suppression (plant height reduction up to 50%). Consequently, the specific species could be certainly used, solely or in mixtures of cover crops for the effective management of invasive and herbicide-resistant weeds. [ABSTRACT FROM AUTHOR]

Conyza canadensis has been reported to be the most frequent weed species that evolved resistance to glyphosate in various parts of the world. The objective of the present study was to investigate the effect of environmental conditions (temperature and light) on the expression levels of the EPSPS gene and two major ABC-transporter genes (M10 and M11) on glyphosate susceptible (GS) and glyphosate resistant (GR) horseweed populations, collected from several regions across Greece. Real-time PCR was conducted to determine the expression level of the aforementioned genes when glyphosate was applied at normal (1; 533 ga.e.ha-1) and high rates (4,8), measured at an early one day after treatment (DAT) and a later stage (four DAT) of expression. Plants were exposed to light or dark conditions, at three temperature regimes (8, 25, 35°C). GR plants were made sensitive when exposed to 8°C with light; those sensitized plants behaved biochemically (shikimate accumulation) and molecularly (expression of EPSPS and ABC-genes) like the GS plants. Results from the current study show the direct link between the environmental conditions and the induction level of the above key genes that likely affect the efficiency of the proposed mechanism of glyphosate resistance. [ABSTRACT FROM AUTHOR]

Sunflower (Helianthus annuus L.) is globally one of the most important oil crops. A 2-years field study was conducted to evaluate growth, grain and oil productivity of three sunflower hybrids (PR64E83, Oleko and PR63A90). Plant height, number of green leaves, weight of 1000-grains and grain number were significantly affected by the interaction of year and sunflower hybrid. Grain yield resulted to differences ranged among 13 and 34 % between the two years. In 2009, Oleko and PR63A90 were the most productive hybrids regarding seed (8210 and 7500 kg/ha, respectively) and oil (2960 and 2950 kg ha-1, respectively), while PR63A90 was the significantly more productive hybrid during the second year (2010). Hybrids such as Oleko seem ideal for high grain and oil yield (with a high concentration of monounsaturated fatty acids); however they fit better to a crop rotation, probably due to a high phytotoxicity of their residues which reduces the yield of the second year. On the contrary, the ability of some non high-oleic hybrids such as PR63A90 to keep high grain yield even in the second year of their cultivation in the same field is clearly a very desirable trait and it should be further tested, since it can result to very high oil yield. [ABSTRACT FROM AUTHOR]

In the present work the genetic activity of the fungicide captafol was studied in a heterozygous diploid strain of Aspergillus (Emericella) nidulans. In vitro fungitoxicity tests of captafol on mycelia growth showed a great increase of the color segregants. Analysis of white and yellow mitotic recombinants suggests that low captafol concentrations (0.075 μg/ml) increase the mitotic crossing-over frequency while non-disjunction was also occurred at high concentrations of 0.15 μg/ml. Light and electron microscopic observations of A. nidulans cells showed that captafol induces a number of cytological abnormalities in hyphae as well as in cell structures. A destruction of cytoplasmatic membrane, nucleus membrane and other membranes was also observed. At concentrations of the fungicide highly inhibitory to growth (more than 50%), an abnormal nuclear division was observed which did not follow the typical mitotic function usually observed in Ascomycetes. On the contrary, the formation of an unequal lobe was present, which leads in an unequal distribution of chromosomal material in the sub-nuclei. [ABSTRACT FROM AUTHOR]

The effects of tillage system and fertilization regimes on weed flora in quinoa (Chenopodium quinoaWilld.) were evaluated by means of two field experiments in 2011 and 2012. The experiments were laid out in a split-plot design with two main plots (conventional and minimum tillage) and four sub-plots (fertilization regimes). The results indicated that weed biomass and density in quinoa were influenced by the different fertilization and tillage treatments. Moreover, seed yield in conventional was 5%–13% higher than that of minimum tillage, probably due to the lower weed density and biomass. Concerning fertilization treatments, total weed density and biomass increased under manure application and inorganic fertilization. Tillage effects on weeds were species specific. The density of perennial weeds such as purple nutsedge (Cyperus rotundusL.) and the density of small-seeded weeds such as redroot pigweed (Amaranthus retroflexusL.) and common purslane (Portulaca oleraceaL.) were significantly lower under the conventional tillage than under the minimum tillage system. [ABSTRACT FROM AUTHOR]

In the present study, there were studied the effects of plant residues of a widely known aromatic plant (Sideritis scardica Griseb) on weed flora and first growth of a sunflower crop. A field and a pot experiment were conducted in Agricultural University of Athens. In particular, the field experiment was conducted under organic conditions, while in the pot experiment special attention was given to the first early growth of sunflower plants under the effect of plant residues. Our results showed that there was a significant effect of plant residues on weed flora and the producted biomass, especially during the first crucial growth stages of sunflower. Particularly, the incorporation of S. scardica residues resulted to a lower number of different weed species (low richness) and an intense effect on most weed species. The pot experiment revealed that sunflower seed germination was not affected by the incorporation of S. scardica residues. Thus, the activity of Sideritis sp. residues was adequately selective (and desirable), since there was not observed any negative effect on sunflower growth. [ABSTRACT FROM AUTHOR]

In 2010, a survey was conducted in the wheat fields of a typical cereal-producing region of Greece to establish the frequency and distribution of herbicide-resistant littleseed canarygrass (Phalaris minor Retz.). In total, 73 canarygrass accessions were collected and screened in a field experiment with several herbicides commonly used to control this weed. Most of the weed populations were classed as resistant (or developing resistance) to the acetyl-CoA varboxylase (ACCase)-inhibiting herbicide diclofop, while resistance to clodinafop was markedly lower. The results of the pot experiments showed that some of the canary populations were found to have a very high level of diclofop resistance (resistance index up to 12.4), while cross resistance with other herbicides was also common. The levels of resistance and cross resistance patterns among populations varied along with the different amounts and times of selection pressure. Such variation indicated either more than one mechanism of resistance or different resistance mutations in these weed populations. The population which had the highest diclofop resistance level, showed resistance to all aryloxyphenoxypropinate (APP) herbicides applied and non-ACCase inhibitors. Alternative ACCase-inhibiting herbicides, such as pinoxaden remain effective on the majority of the tested canarygrass populations, while the acetolactate synthase (ALS)-inhibiting herbicide mesosulfuron + iodosulfuron could also provide some solutions. Consequently, there is an opportunity to effectively control canarygrass by selecting from a wide range of herbicides. It is the integration of agronomic practices with herbicide application, which helps in effective management of P. minor and particularly its resistant populations. [ABSTRACT FROM AUTHOR]

The presence of velvetleaf (Abutilon theophrasti) in crops is increasing in arid and semi-arid environments. Field experiments were conducted in Greece in 2009 and 2010 to determine the influence of velvetleaf emergence time and maize (Zea mays) hybrids with different growth rates on maize yield and velvetleaf growth and fecundity. Velvetleaf was uniformly seeded in order to emerge at the 1, 3, 5 and 7-leaf stage of maize (V1, V3, V5 and V7 growth stages, respectively). Velvetleaf biomass, canopy area and seed production were significantly affected by the date of velvetleaf emergence. Velvetleaf plants emerging just after maize (V1) produced 7–17 times lower seed number, compared with the V5 growth stage. Maximum maize grain yield loss ranged from 26 to 37% for early emerging velvetleaf, and less than 6% yield loss occurred from velvetleaf seedlings emerging at V7 growth stage. Maize hybrids with high initial growth rate seem to be more competitive than the other hybrids. The results of this study are essential in the development of an integrated weed management strategy for maize in semi-arid environments, since they highlight the importance of the careful selection of a competitive maize hybrid and avoidance of early velvetleaf emergence. [ABSTRACT FROM PUBLISHER]