عنوان مقاله [English]
Introduction: Improving the rate of germination and crop growth at the early growing stagescan reduce weed damage via increasing crop competitiveness. Trifluralin is a pre emergence herbicide that is incorporated with soil to prevent weed emergence and seedling growth. It inhibit microtubule assembly in cells . Seed priming cause to initiate the repairing system for membrane and the metabolic preparation for germination through controlling water absorption rate of seed. As a result, the germination capability and resistance to unfavorable conditions of seed can be promoted obviously using seed priming. Ultrasound is defined as acoustic waves at frequencies greater than 20 kHz that can be an effective method to improve germination and growth characteristics of plants . There is no knowledge about the effect of ultrasonic waves and seed priming on the emergence and growth of cowpea (Vigna sinensis) under soil application of trifluralin. So the objective of this research was to study the effect of ultrasonic waves and seed priming on the emergence and growth of cowpea under soil application of trifluralin.
Materials and methods: Field experiment was conducted at the research field of Shahrood University (latitude of 36° 25 'N and longitude of 54° 57' E with an elevation of 1345 m) as randomized complete block design with four replications in during the growing season of 2014-2015. The field soil was silty clay loam in texture, having pH 7.8, EC 3.9 ds m-1, 0.75% of organic carbon, 0.04% N 6.4 and 320 ppm of available P and K. Nine treatments were 1- control, 2- recommended herbicide dose (trifluralin 2 L ha-1), 3- reduced herbicide dose (trifluralin 1 L ha-1), 4- ultrasonic waves (ultrasound), 5- ultrasonic waves + reduced herbicide dose, 6- ultrasonic waves + recommended herbicide dose, 7- hydro-priming, 8- hydro-priming + reduced herbicide dose and 9- hydro-priming + recommended herbicide dose. For hydro-priming treatment, the seeds were treated with water before sowing for 7 h. About ultrasonic treatment, the seeds before sonication (for 6 minutes) treated with water for 7 h. Trifluralin (Treflan, EC48%) applied in recommended dose (2 L ha-1) and reduced herbicide dose (1 L ha-1) as immediate mixed with soil before planting. The plots were 24 m2 with 4 sowing rows and 6 m long. Seeds were placed at 3 to 5 cm depth in each row at during the second week of June in 2014. Number of emerged seedlings in two middle rows of were daily counted until seedling establishment became stable. Emergence percentage and rate of cowpea were calculated. Sampling was done at 55 days after planting. All samples were transferred to the laboratory, leaves and stem were separated,dried into oven at 70 ºC for 72 h and weighted. Chlorophyll content, relative water content, leaf and shoot dry weight and plant height of cowpea were measured for all treatment
The second experiment was conducted at the greenhouse as randomized complete block design with four replications in 2014. The treatments were exactly similar to the field experiment. Germinated seeds were recorded every 24 h for 16 days. Then, the plants were removed from each pot and transferred to the laboratory. Root, leaves and stem were separated and afterwards all samples were dried into oven at 70 ºC for 48 h and weighted. Seedling vigor index, chlorophyll content, shoot and root length, weight of root, leaf and shoot, number of leaf and leaf area index were measured for all treatment. Chlorophyll content was estimated using chlorophyll meter (SPAD-502, Konika-Minolta Co). Statistical analyses of data were performed with statistical software MSTATC. Significant differences between means refer to the probability level of 0.05 by LSD test.
Results and discussion: The results showed that the ultrasonic treatment increased the dry weight of stem and leaves by 25.27 and 29.58 % as compared with the control treatment respectively. Mirshekari et al. (34) reported that when seeds were primed with ultrasonic irradiation for 5 min, seedling dry weight and leaf chlorophyll content of yarrow increased by 70% and 33.6% than control respectively. Marghaeizadeh et al. (33) reported that application ultrasonic waves increased the chlorophyll content of Carum copticum (L.) C. B. Clarke in comparison to control. Our results suggested that at both experiments the combined use of ultrasonic waves + reduced herbicide dose decreased the percentage and rate of emergence significantly in comparison to herbicide application alone. The application of ultrasonic waves + reduced herbicide dose led to a reduction in the percentage and rate of emergence by 64.83 and 68.13% in comparison to reduced herbicide application alone, respectively. Also the combined use of priming + reduced herbicide dose decreased the percentage and rate of emergence by 50.4 and 53.8 % in comparison to reduced herbicide application alone respectively. The major effects of dinitroanaline herbicides are on plant root growth, which they stop by interfering with mitosis and preventing normal cell division and cell wall formation (38, 35). It seems that hydro priming technique and ultrasonic irradiation with improving seed germination and seedling early growth under soil-incorporated trifluralin herbicide can led to more and faster absorption of herbicide by seedling and more damage to them than control.
Conclusion: Our results showed the ultrasonic waves and priming accelerates the seed germination and root length and ultimately resulted in improving biomass and growth of cowpea seedling. Also data presented in this research suggested that pre-treated of cowpea seeds with ultrasonic waves and hydro priming can reduce some plant parameters like percentage and emergence rate of seeds, shoots dry weight, leaf area index and etc. in soil treated with trifluralin herbicide.