-Specific knowledge about the dormancy, germination, and emergence patterns of weed species aids the development of integrated management strategies. Laboratory studies were conducted to determine the effect of several environmental factors on seed germination and seedling emergence of Cyperus difformis. Germination of freshly harvested seeds was inhibited by darkness; however, when seeds were subsequently transferred to complete light they germinated readily. Our results showed that 2 wk of cold stratification overcome the light requirement for germination. Seeds of C. difformis were able to germinate over a broad range of temperatures (25/15, 30/20, 35/25, and 40/30 o C day/night). The response of germination rate to temperature was described as a non-linear function. Based on model outputs, the base, the optimum and the ceiling temperatures were estimated as 14.81, 37.72 and 45 o C, respectively. A temperature of 120 o C for a 5 min was required to inhibit 50% of maximum germination. The osmotic potential and salinity required for 50% inhibition of maximum germination were -0.47 MPa and 135.57 mM, respectively. High percentage of seed germination (89%) was observed at pH=6 and decreased to 12% at alkaline medium (pH 9) pH. Seeds sown on the soil surface gave the greatest percentage of seedling emergence, and no seedlings emerged from seeds buried in soil at depths of 1 cm.Keywords: osmotic potential, salinity stress, pH, soil depth, temperature. (25/15, 30/20, 35/25, e RESUMO -O conhecimento específico sobre os padrões de dormência, germinação e emergência de espécies de plantas daninhas auxilia o desenvolvimento de estratégias integradas de gestão. Foram realizados estudos de laboratório para determinar o efeito de vários fatores ambientais na germinação de sementes e emergência de plântulas de Cyperus difformis. A germinação das sementes recém-colhidas foi inibida pela escuridão; no entanto, quando as sementes foram transferidas posteriormente para a luz total, germinaram prontamente. Nossos resultados mostraram que duas semanas de estratificação fria superam o requisito de luz para a germinação. As sementes de C. difformis conseguiram germinar numa ampla gama de temperaturas

Littleseed canarygrass is a troublesome grass weed in wheat fields in Iran. Predicting weed emergence dynamics can help farmers more effectively control weeds. In this work, four nonlinear regression models (beta, three-piece segmented, two-piece segmented, and modified Malo's exponential sine) were compared to describe the cardinal temperatures for the germination of littleseed canarygrass. Two replicated experiments were performed with the same temperatures. An iterative optimization method was used to calibrate the models and different statistical indices (mean absolute error [MAE], coefficient of determination [R2], intercept and slope of the regression equation of predicted vs. observed hours to germination) were applied to compare their performance. The three-piece segmented model was the best model to predict the germination rate (R2= 0.99, MAE = 0.20 d, and coefficient of variation 1.01 to 4.06%). Based on the model outputs, the base, the lower optimum, the upper optimum, and the maximum temperatures for the germination of littleseed canarygrass were estimated to be 4.69, 22.60, 29.62, and 38.13 C, respectively. The thermal time required to reach 10, 50, and 90% germination was 31.98, 39.26 and 45.55 degree-days, respectively. The cardinal temperatures depended on the model used for their estimation. Overall, the three-piece segmented model was better suited than the other models to estimate the cardinal temperatures for the germination of littleseed canarygrass.

No abstract

Cleome viscosa is one of the most important weeds of warm-season crops in southern Iran. Laboratory experiments were conducted to assess the impact of environmental factors on seed germination of C. viscosa. Freshly harvested seeds exhibited dormancy that was relieved (>90%) after immersion for 20 min in concentrated sulfuric acid. Regardless of the temperature regime, the final percentage of germination in light/dark (69.3%) was significantly higher than in complete darkness (58.3%). The optimum temperature for germination was 35/25 C in both light and dark. No germination was observed at constant temperatures of either 15 or 45 C. The thermal thresholds for seed germination, the base (T b ) and the mean ceiling germination temperatures (T c(50) ) were estimated to be 18.8 and 39.9 C, respectively. A base water potential (Ψ b(50) ) of −0.96 MPa was identified for C. viscosa seeds. The response threshold of C. viscosa to reduce 50% of maximum germination for salinity was estimated to be 255 mM. Seeds that were placed on the soil surface had the highest percentage of seedling emergence (77.3%), and no seedlings emerged from seeds placed at a depth of 6 cm. The findings of this study could help to improve the integrated weed management strategies for this species.

Wild mustard (Sinapis arvensis L.) is well-known as a serious weed of cultivated land, particularly in cereal crops. It produces large amounts of heteromorphic (black and brown) seeds. This study aimed to estimate the critical temperature thresholds of wild mustard heteromorphic seeds. For this purpose, a novel Weibull-based thermal time model was developed, which was applied to compare the germination characteristics of the heteromorphic seeds of wild mustard. Germination was investigated by exposing the seeds to eight constant temperatures of 7.5, 10, 15, 20, 25, 30, 35, and 37.5 °C. Over both the sub- and supra-optimal ranges, the proposed model reasonably explained the germination patterns of both seed types in response to temperature. Heteromorphic seeds of wild mustard exhibited different germination behaviors in response to temperature. Brown seeds were more cold-tolerant and could germinate rapidly to a high percentage (68%) in a wider range of temperature environments (2.78-38.05 °C); black seeds germinated at a narrower temperature range (4.99-37.97 °C), and a large proportion of seeds remained dormant (77%). These differences can lead to the temporal distribution of seed germination throughout the growing season.