Intra-specific Variations among Different Canada Thistle (Cirsium arvense L.) Ecotypes

Canada thistle (Cirsium arvense L.( occurs in pastures and wheat fields and is common in most provinces, where it is considered a major agricultural weed in Iran. Increasing our understanding of the environmental factors that determine Canada thistle emergence can provide strategies to control it. Therefore, in this paper the morphological characteristics of 10 ecotypes collected from different regions of Iran and the effect of temperature on the percentage and rate of emergence of root buds in controlled conditions were investigated. Temperature was considered as the treatment because it is one of the most important factors that fluctuate between the diffusion regions in Iran.

To evaluate any morphological differences among ecotypes of Canada thistle, root fragments were collected from 10 provinces of Iran in 2020. To reduce the effect of the environment, the roots were propagated again in pots in the greenhouse under controlled conditions. Day and night temperatures were 30 and 15 °C, respectively. The root pieces were then harvested and stored at 5 °C for 3 months. Two 10 cm long roots with same weight and same number of buds were planted in pots containing loamy sandy soil. The pots were irrigated during the experiment and the plants were not exposed to water stress. A Completely Randomized Design was conducted at Science Research Branch, Islamic Azad University. After 70 days plants were harvested. The numbers of leaves and branches on the main shoot and number of capitulum were counted and the root length, height of the main shoot and capitulum length were measured. Data analysis of variance was performed using SAS software and means were compared using protected LSD test. Cluster analysis was performed by calculating the Euclidean distance for grouping populations using SPSS software and its dendrogram was drawn. The root and shoot dry weights were measured after drying at 70 °C for 48 h after harvest. At second experiment, temperatures 1- 38° C were evaluated for studying the effect of temperature on percent and rate of shoot emergence. Base temperature (temperature at which the germination rate is zero) was obtained using the linear regression equation between germination rate and temperature.

There were significant differences at morphological traits among Canada thistle ecotypes except capitulum length. Root dry weight varied from 8 g in Gonbad ecotype to 11.5 g in Varamin ecotype. Total dry weight was the lowest in Hamedan and was not significantly different from Mashhad and Gonbad ecotypes. The highest total dry weight belonged to Shiraz ecotype. Cluster analysis grouped 10 ecotypes at four groups. First group consisted of Babol, Gonbad and Moghan ecotypes. Varamin, Shahreza, Mashhad, Hamedan and Shiraz placed at second group. Kermanshah and Dezful were placed at third and fourth groups, respectively. In the next step, the data were correlated into principal components on the correlation matrix. In total, the three main components explained about 80.20% of the total data changes. The first component explained 34.33% of the changes. Main stem height, total dry weight and number of leaves had a positive correlation with this component and shoot dry weight had a negative correlation with it. The second component explained 33.82% of the changes in the total data. Groundwater dry weight and total stem + root length had high coefficients in this component. The third component accounted for 12.03% of the changes, with only the number of capitols in each branch having a high positive correlation with this component. The estimated base temperatures for the emergence of bud root were 5.34, 4.91, 5.98, 5.70, 4.42, 6.52, 3.12, 6.26, 3.80 and 5.91°C for Babol, Varamin, Shahreza, Gonbad, Mashhad, Dezful, Kermanshah, Moghan, Hamedan and Shiraz ecotypes, respectively. Emergence growth degree day for Babol, Varamin, Shahreza, Gonbad, Mashhad, Dezful, Kermanshah, Moghan, Hamedan and Shiraz were 201, 210, 200, 205, 190, 220, 182, 202, 190 and 210, respectively.

Temperature had a significant influence on the root of Canada thistle. When the temperature was below 3°C, no emergence occurred. Temperature affected not only the percentage of emergence but also the emergence rate. There was a significant linear relationship between the emergence rate and incubation temperature. High temperature probably causes activation of the enzymatic and physiological function of root buds and increases the rate of mobilization of nutrient reserves to the growing belowground shoots.