Effect of Pretreatment of Sunflower (Helianthus annuus L.) Seed with Cold Plasma on its Yield and Yield Components in Competition with Weeds

Sunflower (Helianthus annuus L.) is a major worldwide oilseed crop that develops slowly during the initial weeks after planting. Weed competition with sunflower during the first four weeks after crop emergence can reduce sunflower yield significantly. Promoting seed germination is the most direct way to improve sunflower growth and competition with weeds. Per-treatment of seed by cold plasma through accelerating seed germination can increase competitive ability of plant with weeds. Cold plasma treatment significantly increased wheat growth and yields. Thus, increasing plant growth can improve competitive ability of it with weeds. The aim of this study was to investigate the effect of cold plasma treatment on growth and yield of sunflower in competition with weeds.

This experiment was carried out as factorial based on randomized complete block design with three replications at Shahrood University of Technology (latitude of 36° 25 'N and longitude of 54° 57' E with an elevation of 1345 m) in 2016. Experimental factors were including cold plasma at six levels: control, hydro-priming of seeds for 10 hours, pretreatment of seeds with cold plasma radiation for 15 and 30 seconds, hydro-priming of seeds for 10 hours + cold plasma radiation for 15 and 30 seconds and weed control at three levels: control (no weeding), weeding all season and application of trifluralin (1200 g. a.i. ha-1). Dielectric barrier discharge plasma jet was operated in ambient air under sterile conditions in the laboratory of Faculty of Physics, Shahrood University of Technology. After seed priming in distilled water for 10 hours, sunflower seeds were taken in petri plates and treated with the plasma for determined times. Seeds were planted in the field immediately after cold plasma treatment. Seed number per head, 100 seeds weight, harvest index, biological, grain and oil yield of sunflower and weed dry weight were recorded. 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.

The results showed that seed number per head, biological and grain yield, harvest index, oil yield and weed dry weight significantly affected by interaction effects of treatments. Results showed that biological, oil and seed yield of sunflower decreased by 62.76, 56.11 and 55.86% in weed-infest than weed-free treatments respectively. Seed number per head and biological yield of sunflower significantly increased by using different pretreatments methods than control in the weed-infest conditions. Also, pretreatment of seeds with cold plasma for 30 seconds increased oil and seed yield of sunflower by 68.8 and 58.5 percent respectively in the weed infest treatment than control. The plasma treatment of soybean seeds up to 2 min showed positive effects on their germination rate and seedling growth. Cold plasma has essential roles in a broad spectrum of developmental and physiological processes in plants, including reducing the bacterial bearing rate of seeds, changing seed coat structures, increasing the permeability of seed coats, and stimulating seed germination and seedling growth. In addition, plasma treatment also could improve the physiological metabolism of the plant, such as de-hydrogenase activity, superoxide dismutase and peroxidase activities, photosynthetic pigments, photosynthetic efficiency and nitrate reductase activity. It seems that hydro-priming technique and cold plasma irradiation with improving seed germination and seedling early growth can led to more and faster germination and better competition of sunflower plants with weeds. 

Based on our results, pre-treatment of seeds by cold plasma and hydro-priming in addition to reducing weed biomass, could significantly improve the growth characteristics and yield of sunflower through increasing crop competitive ability with weeds.