Iranian Journal of Seed Research

Introduction: Interference caused through weeds’ and crops’ competition for environmental resources and allelopathy brings about damage in crop species. Allelopathy is defined as a direct or indirect inhibiting or provoking effect of a plant on other plants through the production of chemical compounds introduced into the environment. Although the allelopathic effects of the shoot extracts of Xanthium spp and Chenopodium album on the germination of some crops have already been investigated, very few studies have so far been conducted to evaluate their adverse effects on soybean seedling growth. The aim of this study was to investigate the effect of different concentrations of aqueous extract of cocklebur and lambsquarters on germination and soybean seedling growth indices under Petri and Pot conditions.

Materials and Methods: In order to study the allelopathic effects of Cocklebur and Common lambsquarters on germination and seedling growth of soybean, two separate experiments were conducted under petri and pot conditions. In this experiment, the effects of aqueous extract concentrations (25, 50, 75 and 100%) of cocklebur and common lambsquarters were evaluated on seed germination of soybean in a completely randomized design with three replications. In each pot, five soybean seeds were planted with a depth of 2 cm. The extracts were added to the pots for 2 weeks after emergence.

Results: Allelopathic effect of common lambsquarters extract concentrations was higher than that of cocklebur in both experiments. Germination percentage (GP) reduction under 25, 50, 75 and 100% concentrations of common lambsquarters was 57, 84, 96.7 and 100%, respectively. GP reduction under the same concentrations of cocklebur was 17, 20, 34 and 54%, respectively. In the pot culture conditions, the root dry weight of soybean decreased with increases in extract concentration, so that the highest root dry weight belonged to the control treatment with 64 mg and the lowest values belonged to the effect of aqueous extract of weed with a concentration of 100%. The results on the EWRC scale showed that the soybean leaflet damages increased as the extract concentrations increased. The highest leaf damages were obtained in 75 and 100% of cocklebur and Chenopodium concentrations. The negative impacts of common lambsquarters were higher than those of cocklebur.

Conclusion: In general, the results of this study showed that the effects of different concentrations of the lambsquarters extract on germination and soybean growth of the Williams cultivar were higher under both Petri and pot conditions. The percentage of germination in the concentrations of 25, 50, 75 and 100% of the aqueous extract of cocklebur was 17%, 20%, 34% and 54%, respectively, and in lambsquarters, it decreased by 57%, 84%, 96% and 100%, respectively, compared to the control. On the other hand, spraying the extracts of lambsquarters and cocklebur caused necrosis and drying of soybean leaves. According to the results, in the absence of effective control of weeds, especially lambsquarters, in soybean farms, the damage caused by allelopathic elements will lead to a significant reduction in germination and seedling growth.

Extended Abstract
 Introduction: Germination is considered the first and most important stage of establishment and consequently, successful competition which is influenced by genetic and environmental factors. Among the environmental factors influencing the germination, temperature and light are the most important ones. Using different models, the germination response of seeds to temperature can be quantified; therefore, this study was performed to investigate the effect of temperature on germination and to quantify the germination response of Buckwheat seed (Fagopyrum esculentum Moenc) to temperature using nonlinear regression models and thermal-time model.
Materials and methods: The seeds were germinated in 4 replications of 25 seeds under 8 constant temperature treatments (5, 10, 15, 20, 25, 30, 35 and 40 ° C). Using a three-parameter logistic model, Buckwheat seed germination was quantified at different temperature levels and the percentage and time to reach 50% germination were obtained. Four nonlinear regression models and a thermal-time model were used to quantify the response of Buckwheat seed germination rate to temperature. To compare the models and determine the most appropriate model, the root mean square error index (RMSE), coefficient of determination (R²), coefficient of variation (CV) and standard error (SE) were used for the observed germination rate versus the predicted germination rate.
Results: The results indicated that temperature affected the seedling length, normal seedling percentage, seed vigor and the germination rate as well as germination percentage. Also, the results showed that germination characteristics increased with increasing temperature up to 20 and 25 °C. Comparison of the three models based on the root mean square error (RMSE) of germination time, the coefficient of determination (R²), CV and SE, the best model to determine the cardinal temperatures of Fagopyrum esculentum was the dent-like model. The results of thermal-time model showed that the base temperature of Fagopyrum esculentum seeds was 4.01 ° C and the thermal-time coefficient was 1242.6 h° C.
Conclusion: Utilization of non-linear regression models (segmented, dent-like and beta) and thermal-time model to quantify the germination response of Fagopyrum esculentum response to different temperatures led to acceptable results. Therefore, germination rate and percentage may be predicted using the outputs of these models at different temperatures.

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