مجله پژوهش علف های هرز
سال پنجم شماره 1 (بهار و تابستان 1392)

Controlled growth chamber experiments were conducted to determine factors affecting seed germination and seedling emergence of Junglerice. In this research the effects of temperature, light, osmotic potential, salinity, burial and water depth on Junglerice seed germination and seedling emergence, and response thresholds of this species to these factors were investigated. Results showed that the seeds of Junglerice have water impermeable seed coat, and chemical scarification using sulfuric acid was effective treatment for dormancy breaking. Seeds of Junglerice are positively photoblastic, and light is simulating factor for germination of this species. Junglerice seeds enable to germination in the wide range of alternating temperatures (25/15, 30/20, 35/25 and 40/30 ˚C) under light/dark condition. The dent-like model was used to describe germination rate-response to temperatures. Based on the dent-like function, the base, the lower optimum, the upper optimum and the maximum temperatures for seed germination were 9.31, 30.45, 38.46 and 45 ˚C, respectively. The response thresholds of Junglerice to reduce 50% of maximum germination for high temperatures, osmotic potential and salinity were 102.17 ˚C (for a 5-min interval), -0.46 MPa and 242.26 mM, respectively. Germination of junglerice was not influenced by the tested pH solutions. Seedling emergence was greatest for seeds placed on the soil surface. As depth of flooding increased, seedling emergence of Junglerice decreased and no seedlings emerged from a depth of 6 cm.

An experiment was conducted to determine allelopathic effect of rye at different concentrations (0, 25, 50, 75, and 100 %) on different wheat cultivars (Alvand, Sayson, Navid, and Toos). Osmotic pressures equivalent to rye extract concentration (0, 0.48, 0.95, 1.36, 1.61 bar) were also prepared by PEG 6000. Sayson cultivar showed more sensitivity to all extract concentrations than other cultivars. By increasing rye extract concentration, cumulative germination percentage of all wheat cultivars were affected significantly as compared with control. PEG had no significant effect on cumulative germination percentage except at 1.6 bar for Toos cultivar. Other wheat cultivar characteristics (germination rate, plumule and radicle length and dry weight) were all affected significantly as compared with control and PEG osmotic pressure.

To study the effect of different temperatures on germination of susceptible and resistant biotypes of wild mustard (Sinapis arvensis) and to determine their cardinal temperatures and to evaluate their fitness in drought, salinity and pH, four separate experiments were conducted in CRD with 4 replications. The seeds were collected from Aghgala, Aliabad and Gorgan and the experiments were conducted with seeds of F1 generation of each biotype. Temperature treatments were 0, 3, 5, 10, 15, 20, 25, 30 and 35 oc and seeds were kept in dark condition. Germinated seeds were counted twice a day with 12 hours intervals. Base, optimum and maximum temperatures for susceptible and resistant biotypes of Sinapis arvensis estimated as 2.2, 2.3, 23, 25 and 40, 39 oc, respectively. There were significant differences between physiological characteristics associated with drought, salinity and pH of resistant and susceptible biotypes of wild mustard. Increasing the drought stress from -0.4 to -1 MPa decreased the germination of all biotypes. Susceptible biotypes showed high sensitivity to acidic pH and had low germination in these pH.

A constrain for basic research on broomrape is unsatisfactory seed germination of this parasitic weed, particularly in the absent of host plant. In this research, the effect of few factors on seed germination of Egyptian broomrape (Orobanche aegyptiaca) was studied in vitro and in the absence of host plant as a factorial experiment. Immersing the seeds in sulfuric acid at 100 or 50 percent concentration for 30 or 60 seconds, exposing them to gibberellic acid at 0 (control) 100, 250 or 500 ppm and incubation at 15, 20 or 25 oC were the treatments. The results indicated that gibberellic acid at all concentrations significantly reduced the seed germination. Immersing the seeds in sulfuric acid at 50% concentration for 60 seconds and incubation at 15 oC, with 44% germination, significantly enhanced the germination more than the other treatments. On seed germination, the effect of temperature was more pronounced than two other factors.

To investigate the effect of different planting date of cover crops on weed seed bank and population dynamic in corn a field experiment based on randomized complete blocks design with three replications was conducted in Sari Agricultural Sciences and Natural Resources University during growth season of 2010. Treatments consisted of three cover crops, soybean, fenugreek and cowpea in two different planting date (simultaneous with corn and 21 days after planting of corn), along with two control (no weeding and weeding). The results showed that weed seed bank was influenced by cover crops, so that soybean, fenugreek, and cowpea at first and second planting date, and control treatment (no weeding) decreased the numbers of seeds in soils by 49, 52, 26, 27, 49, 51 and 5%, respectively. The results showed that dominant weed populations such as velvetleaf and johnsongrass were also affected by planting date of these cover crops in contrast with control (no weeded). All three cover crops and weeding check increased corn yield significantly as compared with no weeding check. The highest corn yield obtained under weeding check treatment and cowpea cover crop at second planting date. Weed seed bank density at some species was significantly reduced at second sampling stage as compared with first sampling stage.

Hirschfeldia incana is one of the dominant and invasive weeds in canola fields of Fars province. The successful management of the weed is dependent in understanding of biology. In this study seed production potential, optimum conditions for germinating, seed viability and dormancy were investigated. The effect of osmotic potentials of water and seed burial depth were studied on seed germination and seedling emergence. The seed production was estimated more than 27000 grain/plant with 95% viability. Results showed that the cold ecotype had less primary dormancy than the warm ecotype. The seed germination occurred between 5 to 40°C and the most germination occurred at 30°C with continuous light. Most of the seedlings were appeared from the seeds at 2.5 cm depth. There was not any germination at 7cm depth or more. Seed germination was sensitive to osmotic potential of water in both of the ecotypes. The highest germination occurred at the zero MPa osmotic potential. By reducing the osmotic potential, seed germination was also decreased, and at to -0.2MPa no seed germination was observed.

In order to survey canary grass (Phalaris minor) and paradoxgrass (P. paradoxa) biotypes resistant to clodinafop-propargyl herbicide in wheat fields of Aq-qala, an experiment was conducted at Gorgan University of Agricultural Sciences and Natural Resources. 41 P. minor biotypes and 15 biotypes of P. paradoxa suspected resistance to the herbicide collected from wheat fields by moving on two hypothetical diameter of Aq-qala map. For each species, one susceptible biotype also collected from areas which had never been applied by herbicides. Experiments included determining discriminating concentration, screening the suspected biotypes with discriminating concentration and concentration-response bioassay for resistant biotypes. According to the results of seed bioassay, discriminating concentration estimated as 0.04 and 0.06 mg.ai.L-1 for P. minor and P. paradoxa, respectively. Results of concentration-response showed that 18 biotypes of P. minor and 2 biotypes of P. paradoxa were resistant to clodinafop-propargyl herbicide. Resistant biotypes showed different resistance factors to clodinafop-propargyl herbicide. Distribution maps of infected fields to resistant P. minor and P. paradoxa biotypes were processed using GIS. The results indicated that the most of resistant biotypes distributed in center and south west of Aq-qala. Results of this study could be used for running programs to manage resistant weeds and to prevent the development of resistant biotypes to other parts of the region.

Pesticides are extensively used to protect crops and to prevent disease. The use of these compounds in modern agricultural systems is indispensable. It is estimated that a small portion of applied pesticides gets to the target pests and most of them enter various compartments of the environment. Pesticides losses from areas of application can be a threat to the different organisms in ecosystems as well as human health. Increasing concern about the pesticides has been emerged with the role of pesticides in disrupting endocrine systems of mammals. The endocrine system acts a significant role in normal growth and development and in reproduction. Once released to the environment, pesticides may be affected by various processes including abiotic and biotic degradation, adsorption and transfer to the water systems as well as air and food. The relative importance of each of these processes is related to physico-chemical nature of pesticide and climate conditions. Environmental changes can also influence the fate, persistence, and toxicity of pesticide and increase or decrease their side effects on organisms in the environment. Due to the high cost of pesticides trace in different matrices of the environment, it has been recently taken into consideration some indicators for quantifying the risks of pesticides for the environment and human health. These models are able to investigate the trend of pesticides risk in time and assess the ecosystem health. The present paper is an overview of the different factors affecting the behavior of pesticides in the environment as well as a critical review of different indicators for the assessment of pesticides risks. We also explore the extent to which these indicators can used in Iran with regards to the lack of data and advantage/disadvantage of the indicators will be presented.