Foliar zinc spraying improves assimilative capacity of sugar beet leaves by promoting magnesium and calcium uptake and enhancing photochemical performance.

Sugar beet, a zinc-loving crop, is increasingly limited by zinc deficiency worldwide. Foliar zinc application is an effective and convenient way to supplement zinc fertilizer. However, the regulatory mechanism of foliar zinc spraying on sugar beet leaf photosynthetic characteristics remains unclear. Therefore, we investigated the effects of foliar ZnSO4·7H2O application (0, 0.1%, 0.2%, and 0.4%) on the photosynthetic performance of sugar beet leaves under controlled hydroponic conditions. The results indicated that a foliar spray of 0.2% Zn fertilizer was optimal for promoting sugar beet leaf growth. This concentration significantly reduced the leaf shape index of sugar beet, notably increasing leaf area, leaf mass ratio, and specific leaf weight. Foliar spraying of Zn (0.2%) substantially elevated the Zn content in sugar beet leaves, along with calcium (Ca) and magnesium (Mg) contents. Consequently, this led to an increase in the potential photochemical activity of PSII (Fv/Fo) (by 6.74%), net photosynthetic rate (Pn) (11.39%), apparent electron transport rate (ETR) (11.43%), actual photochemical efficiency of PSⅡ (Y (Ⅱ)) (11.46%), photochemical quenching coefficient (qP) (15.49%), and total chlorophyll content (25.17%). Ultimately, this increased sugar beet leaf dry matter weight (11.30%). In the cultivation and management of sugar beet, the application of 0.2% Zn fertilizer (2.88 mg plant-1) exhibited the potential to enhance Zn and Mg contents in sugar beet, improve photochemical properties, stimulate leaf growth, and boost light assimilation capacity. Our result suggested the foliar application of Zn might be a useful strategy for sugar beet crop management.

Phytotoxicity response of sugar beet (Beta vulgaris L.) seedlings to herbicide fomesafen in soil.

Fomesafen is the most widely used herbicide in the soybean field. However, there are urgent practical challenges with the long-term persistence of fomesafen in soil and its effects on the subsequent crops in agricultural production. Therefore, pot experiments were conducted to study the effects of fomesafen residues (0-0.05 mg kg-1) on growth, photosynthetic characteristics, and the antioxidant defense system of sugar beet seedlings. The results showed that with the increase of fomesafen residues, the phytotoxicity index increased, while the plant height, leaf area, root length, root volume, and dry weight of sugar beet decreased. Photosynthetic pigment content, net photosynthetic rate (Pn), maximum photosynthetic efficiency (Fv/Fm), and actual photosynthetic efficiency (Y(II)) declined with a dose-dependent manner of fomesafen, but the intercellular CO2 concentration (Ci) and non-photochemical quenching coefficient (NPQ) increased under fomesafen. On the other hand, the residues of fomesafen increased the content of malondialdehyde (MDA) and membrane permeability by aggravating oxidative stress and triggering the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and polyphenol oxidase (PPO). In addition, sugar beet seedlings were significantly sensitive to fomesafen as the concentration of fomesafen in the soil was up to 0.025 mg kg-1. In conclusion, the present study showed that fomesafen residues in the soil could affect the morphophysiology and photosynthetic performance of sugar beet. This study is beneficial for understanding the effects of the herbicide fomesafen residues on non-target crops.

Exogenous salicylic acid alleviates fomesafen toxicity by improving photosynthetic characteristics and antioxidant defense system in sugar beet.

Fomesafen herbicide application has become major pollution in the growth and production of crops. Spraying fomesafen on the target crops may drift out to non-target crops. In northeast China, sugar beets are always planted adjacent to soybeans. Salicylic acid (SA) plays an important role in crop growth and alleviating abiotic stress, however, the role of SA in relieving fomesafen stress in sugar beet growth has rarely been investigated. Therefore, a pot study was conducted to elucidate the effects of different concentrations (0.025, 0.25, 0.5, 1, 5, and 10 mM) of SA on morphological parameters, photosynthetic performance, and antioxidant defense system in sugar beet seedlings under fomesafen (22.5 g a.i. ha-1) stress. The results showed that fomesafen stress inhibited the growth of sugar beet seedlings, and photosynthetic performance, while increased membrane lipid peroxidation and oxidative stress. However, exogenous SA alleviated the fomesafen stress and increased plant height, biomass, photosynthetic pigment contents, net photosynthetic rate (Pn), and photochemical efficiency of PSⅡ (Fv/Fm) in sugar beet leaves. Meanwhile, exogenous SA maintained the cell membrane integrity by reducing the content of malondialdehyde (MDA) and electrolyte permeability and regulating the activities of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and polyphenol (PPO). Therefore, it is concluded that exogenous SA ameliorated the adverse effects of fomesafen on the growth of sugar beet seedlings, with a pronounced effect at 1 mM SA. The present study results may have useful implications in managing other plants that are poisoned by herbicides.