Comparison of Growth and Phenological Development of Jimsonweed (Datura stramonium L.) Ecotypes

Jimsonweed (Datura stramonium L.) is considered as a serious weed in many crops such as corn, soybean, Chitti been and cotton and in waste land. Due to jimsonweed is resistant to most commonly used herbicides, its control is difficult. Contamination of wheat, rye, buckwheat and linseed with seeds of jimsonweed resulting in poisoning have been reported. A precise prediction of the phenological development of jimsonweed in crops would provide timely control for more efficient management of it in growing season.

The experiment was carried out at Iranian Plant Protection Research farm in Karaj (Meshgin dasht) during 2013. The experiment was a split plot layout as randomized complete block design with three replications per planting date (March, April, May, June, July and August) and ecotypes (Karaj, Ghazvin, Shiraz, Gorgan, Esfahan, Mashhad and Oromiee) as the main plot and the subplot. Jimsonweed seeds were cultivated manually in four rows at a distance of 30 cm and a depth of 3-5 cm. The plants were noted twice a week to record the phonological stages of growth. Seven main stages were selected and studied according to the study of phonological stages of jimsonweed based on BBCH codes. The base temperature of jimsonweed was considered 8 ºC. Time to main phonological stages of jimsonweed ecotypes including emergence, three-leaf, eight-leaf, flowering, fruiting, opening fruit and maturity were compared using linear regression model.

One of the reasons for using linear regression to describe the phenological development of plants is that, during plant life and at the time of seedling emergence, the reaction of the rate of development of most plants is linear or near the linear temperature, which is the nature of the traditional thermal time method (GDD). This suggests that with increasing environmental temperature, there is a difference between the seeds of different ecotypes of jimsonweed during emergence of seedlings. Emergence rate was higher in Oromiee ecotype than the other ecotypes. Oromiee and Gorgan ecotypes reached to three-leaf stage sooner than the other ecotypes. Oromiee ecotype with smaller canopy reached sooner to reproductive stage that can be used as a mechanism for survival and seed production for future generations against the falling temperature during the last months of plant growth. The ecotype of Shiraz showed less reaction to temperature in this stage than other ecotypes due to higher average temperature in Shiraz city compared to Karaj city. Oromiee ecotype was more sensitive to temperature than other jimsonweed ecotypes. In other words, the rate of reaching to the phenological stages in this ecotype was higher for each unit of temperature. The rapid reaction of this ecotype to the increase of temperature could be due to the conditions of the growth of the mother plant of this ecotype compared to the other jimsonweed ecotypes. This trend was reversed in the ecotype of Shiraz, which means that this ecotype was less sensitive to temperature, and grew at a slower rate than the other jimsonweed ecotypes. The mother plants of this ecotype, in contrast to the Oromiee ecotype, were produced at a higher average temperature, which resulted in a lower reaction due to an increase in temperature per unit of temperature.

Different ecotypes of jimsonweed have different phonological responses relative to the temperature. In addition, the rates of phonological development of ecotypes with different geographic regions were significantly different. In general, jimsonweed ecotypes showed the highest and lowest sensitivity to the increase in temperature at emergence and reproduction stages, respectively. Having knowledge of plant phenology, through the establishment of land preparation and planting date, will be effective for sustainable weed management. Additionally, the determination of the best time for spray also depends on the precise knowledge of the phonological stages. In many cases, the ineffectiveness of herbicides is due to the growth stages of the weed and the reduction of their sensitivity to them. Disturbance in the dynamics of the seed bank of weeds also requires knowledge of the germination characteristics and plant phonological stages. Recognizing these different behaviors in different ecotypes of weeds is very important and plays a very important role in recognizing patterns of weed adaptation to environmental conditions and also choosing appropriate management strategies.