Danijela Pavlovic

Effect of plant growth promoting rhizobacteria on Ambrosia rtemisiifolia L. seed germination

SUMMARY Soil bacteria are able either to stimulate or inhibit seed germination. If seed germination is stimulated, the seedlings of weed species emerge more uniformly, so that they could be killed in the next step of weed control. This investigation focused on testing the germination of Ambrosia artemisiifolia L. on several media: Pseudomonas fluorescens (B1), Azotobacter chroococcum (B2), Bacillus licheniformis (B3), B. pumilus (B4), B. amyloliquefaciens (B5). In control, seeds germinated in water. Seed germination varied depending on bacterial media. Germination was inhibited by bacterial treatments B1 and B3, treatments B2 and B4 stimulated germination, while germination in treatment B5 was similar to control.

Chlorophyll as a measure of plant health: Agroecological aspects

As photosynthesis is the basic process during which light energy is absorbed and converted into organic matter, the importance of the plant pigment chlorophyll (a and b forms) as an intermediary in transformation of the absorbed solar energy and its activity in the process of photosynthesis and synthesis of organic substances in plants are crucial. Therefore, this paper provides an overview of methods for monitoring the optical activity of chlorophyll molecules and methods (non-destructive and destructive) for quantification of chlorophyll in plants. These methods are used to estimate the effects of different stress factors (abiotic, biotic and xenobiotic) on the efficiency of photosynthesis and bioproductivity, aiming to assess the impact that these limiting factors have on the yield of various cultivars. Also, those methods for analysis of chlorophyll optical activity and/or content are appropriate for assessing the reaction of weed species to different agricultural practices (mineral nutrition, treatment by herbicides, etc.) and studies of different aspects of weed ecophysiology and their influence on crop harvest. [Projekat Ministarstva nauke Republike Srbije, br. TR 31018 and br. TR 31037]

Effect of nicosulfuron on plant traits of Xanthium strumarium

Field experiments were conducted in 2008 and 2009 at the Experimental Field Institute Padinska Skela PKB Agroe-konomik, near Belgrade, to quantify effects of nicosulfuron on plant traits (vegetative production and fecundity) of Xanthium strumarium. Plants of X. strumarium were grown in monoculture on plots of 5 × 4.2 m. Inter-row spacing was 24 cm and the distance between the rows was 70 cm. Plants were treated with nicosulfuron when they developed two pairs of leaves. The applied rates of nicosulfuron were 20, 40 and 80 g a.i. ha−1 and one control treatment (without herbicide application) was included. Vegetative parameters (height, fresh weight, leaf area and leaf area index (LAI)) were recorded just before herbicide application and four times after the herbicide treatment. Measurements were made at intervals of about two weeks. At maturity, fecundity of weeds (bur weight plant−1 and bur number plant−1) was measured. In both years, the application of nicosulfuron caused less growth (height, fresh weight and LAI) of X. stru-marium in comparison with the control. All rates of nicosul-furon reduced vegetative parameters, which decreased as rates of nicosulfuron increased. On the other hand, effects of nicosulfuron on bur production were not equivalent to its effects on vegetative parameters. Only the highest rate of nicosulfuron reduced bur production significantly.

Identification of Glyphosate Resistance in Lolium rigidum Gaudin

Glyphosate resistance was found in Lolium rigidum Gaudin (Rigid ryegrass, LOLRI) in South Africa. Suspected glyphosate-resistant L. rigidum populations were collected and grown under greenhouse conditions. The plants were sprayed with a range of doses of glyphosate 35 days after planting and shoot dry biomass was determined 17 days after herbicide treatment. Based on the dose-response experiment conducted in the greenhouse, one population of L. rigidum suspected to be resistant to glyphosate was approximately 5.3 fold more resistant than susceptible population. The other population was 2.8 fold more resistant than susceptible population. Difference between the two suspected resistant populations was 1.9 fold. All plants were treated with glyphosate (1000 g a.i. ha-1) and shikimic acid was extracted 2, 4 and 6 days after treatment. The plants of susceptible populations accumulated more shikimic acid than other two populations.

Temperature effects on Cuscuta campestris Yunk. seed germination.

Studies of biological characteristics of seeds and conditions for their germination have a major importance for planning and executing rational measures of weed control. The aim of this study was to investigate the effect of different temperatures on germination of C. campestris seeds. Three treatments (T1- storage at room temperature; T2 - exposure to 4°C for 30 days; T3 - scarification by concentrated sulphuric acid) differing in manipulation with seeds before germination were tested at different temperatures (5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C). Germinated seeds were counted daily for ten days and the length of seedlings was measured on the last day. The results showed that differences in germination of C. campestris seeds were very prominent between temperatures, as well as between treatments T1, T2 and T3. Seeds failed to germinate at 5°C and 45°C in all treatments (T1, T2, T3). Germination ranged from 6.25 at 10°C to 96.88%, the highest percentage, achieved at 30°C. [Projekat Ministarstva nauke Republike Srbije, br.III 46008 i br. TR 31043]

Gene Flow from Herbicide-Resistant Sunflower Hybrids to Weedy Sunflower

Weedy forms of cultivated sunflower (Helianthus annuus) are invasive species widely distributed in several regions of the world and are commonly controlled by applying acetohydroxyacid synthase (AHAS)-inhibiting herbicides, such as imidazolinones (IMIs) or sulfonylurea (SUs). The widespread adoption of herbicide-resistant crops has exposed the weedy population to the high risk of crop-to-weedy gene flow. The aim of this study was to check and quantify the gene flow from IMI- and SU-resistant sunflower hybrids to weedy sunflower populations. Field experiments were conducted in 2008 at two sites in Serbia to evaluate the relationship of distance between the crop and the weedy sunflower and its impact on the percentage of gene flow. The weedy sunflower progenies were evaluated through herbicide resistance and SSR marker study. Hybridization with IMI-resistant hybrids was not confirmed. Conversly, SU-resistance trials and SSR marker studies partially confirmed the transfer of resistance within the weedy population.

Gene Flow from Herbicide-Resistant Crops to Wild Relatives

Development of herbicide-resistant (HR) crops is way to overcome problems in weed control due to weed resistance to herbicides and absence of new herbicides with a new mode of action for their control. Three types of HR crops were developed: nontransgenic, transgenic, and multiple HR crops. Cultivation of HR crops is associated not only with many benefits (simplification of weed control, more effective and efficient weed control, higher yields, etc.) but also with various risks (development of HR weeds, development of HR volunteer crops, gene flow from HR crops to susceptible relatives, etc.). The greatest risk is gene flow from HR crops to related weed species, wild relatives or conventional crops of the same species. Unwanted gene flow could be prevented or reduced using different barriers such as isolation in space or time, protective vegetation barriers, male sterility, etc. Sunflower hybrids resistant to herbicides (imidazolinones and sulfonilureas) was developed by conventional breeding methods, and their introduction in Serbian fields has enabled a more efficient control of harmful weed species, but the presence of huge populations of weedy sunflower is the main concern associated with their cultivation, because numerous studies have confirmed gene flow from sunflower to its relatives.

The effect of plant growth promoting rhizobacteria on Datura stramonium L., Abutilon theophrasti Med., Onopordon acanthium L. and Verbascum thapsus L. seed germination.

The effects of several bacterial media [Bacillus licheniformis population 1 (MO1); B. licheniformis population 2 (MO2); B. subtilis (MO3); B. megatherium (MO4); humates (MO5)] on seed germination of Datura stramonium L., Abutilon theophrasti Med., Onopordon acanthium L. and Verbascum thapsus L. were tested. Seeds were germinated in Petri dishes containing solutions with different bacterial media. The highest germination percentage in all treatments was recorded for V. thapsus seeds (100.0%). Different treatments had diverse effects (stimulative or inhibitory) on seed germination of D. stramonium [from 5% (MO1) to 13.3% (MO3), with 10.0 % in H20], A. theophrasti [from 28.3% (MO3) to 65.0% (MO5), with 43.3 % in H20] and O. acanthium [from 10.0% (MO2) to 13.3% (MO1 and MO3), with 6.7% in H20], depending on the type of media and weed species. [Projekat Ministarstva nauke Republike Srbije, br. III46008 i EU project FP7-REGPOT-AREA 316004]