تأثیر تغذیه نشاء چغندرقند (Beta vulgaris L.) از سیلیسیم بر تحمل گیاهچه پس از نشاکاری آن به تنش ناشی از باد بردگی فورام‌سولفورون

Extended abstract
Introduction
Sugar beet is a major crop cultivated for sugar production. Herbicides, though a modern and efficient method of weed control, can easily cause toxicity to non-target crops through drift. Herbicide drift not only contributes to environmental pollution but is also considered a significant factor in reducing crop productivity. Sugar beet is particularly susceptible to herbicides. In recent years, the detrimental effects of herbicide drift-such as from nicosulofuron, a corn-selective herbicide, and fumsafen, a soybean-selective herbicide, have been reported on sugar beet. The application of silicon has attracted considerable interest among growers due to its potential to enhance crop resistance against both biotic and abiotic stresses, including herbicide exposure. Initially, the protective role of silicon was attributed to its mechanical effects, particularly its ability to form a physical barrier by strengthening plant cell walls. However, more recent research has revealed that silicon also provides biochemical protection to plants. Silicate-solubilizing bacteria may offer a sustainable and cost-effective alternative to synthetic silica nanoparticles, which are not only expensive to produce but also raise concerns regarding environmental and biological safety. Therefore, this study was conducted to investigate the effects of silicon-based nutrition on enhancing the tolerance of sugar beet transplants to stress caused by foramsulfuron drift.
Materials and Methods:
The first experiment was conducted as a factorial in a completely randomized design with four replications. The first factor included two types of seedbeds used for producing sugar beet cultivar Shokofa transplants (inoculation and non-inoculation with 100 mg/kg of K2SiO3 + 10 ml/kg of a commercial silicate-solubilizing bacteria), and the second factor included six doses of foramsulfuron (0, 0.05, 0.56, 5.62, 56.25 and 562.5 g a.i. ha^-1). Transplanting was performed at the 4-leaf stage of sugar beet and herbicide treatments were applied at the 6-leaf stage using a hand-held pressure sprayer. In the second experiment, in addition to the two aforementioned factors, a third factor was included: three levels of foliar application involving either no treatment or pretreatment with malathion (applied 2 hours before foramsulfuron) and 4-chloro-7-nitrobenzofurazan (applied 2 days before foramsulfuron).
Results and Discussion:
Silicon nutrition significantly improved several physiological and biochemical traits in sugar beet, including shoot dry weight (by 28.4%), silicon content (by 178.1%), lignin content (by 122.2%), phenylalanine ammonia-lyase activity (by 90.9%), and catalase activity (by 14.5%). It also reduced hydrogen peroxide (by 15.4%) and malondialdehyde content (by 11.7%). The observed growth enhancement was likely due to improved nutritional conditions in silicon-fed plants. The activity of silicate-solubilizing bacteria, which convert various silicates into plant-available silicic acid, slightly decreased soil acidity. This shift promoted greater uptake of essential nutrients such as nitrogen, phosphorus, potass ium, and boron. Application of 0.05 g ha^-1 foramsulfuron to sugar beets not supplied with silicon resulted in 23.9% reduction in dry weight. Under herbicide stress (except for 56.2 and 562.5 g a.i. ha^-1), sugar beets that received silicon nutrition exhibited higher dry weight compared with non-silicon fed plants. This suggests that silicon alleviates herbicide toxicity, potentially through enhanced lignification cell-walls-thereby reducing herbicide absorption-and or by strengthening the plant’s antioxidant defense system, leading to decreased oxidative stress. Under low herbicide doses (0.05 and 0.56 g a.i. ha⁻¹), pretreatment with  4-chloro-7-nitrobenzofuran and malathion prior to herbicide application had a noticeable effect on sugar beet dry weight. However, in general, these pretreatments led to a reduction in dry weight, with 4-chloro-7-nitrobenzofurazan showing more pronounced effect than malathion.
Conclusion
The findings indicate that foramsulfuron induces severe oxidative stress in sugar beet, beyond the plant's inherent capacity to metabolize or detoxify it effectively. While silicon nutrition helped mitigate this stress to some extent, it was not sufficient on its own to fully counteract the herbicide's phytotoxic effects.