ABSTRACT Asian soybean rust (ASR), triggered by Phakopsora pachyrhizi, can cause great yield losses on soybean and nickel (Ni) has potential to control this disease. This study evaluated the effect of using soybean seeds with different Ni contents on ASR control by performing two experiments. In experiment 1, seeds with different Ni contents were obtained by spraying plants three times with solutions containing either 60 or 100 gNi·ha-1. Plants sprayed with water served as the control treatment. In experiment 2, plants originated from seeds obtained in experiment 1 (T1 = 0.9 µgNi·seed-1, T2 = 1.2 µgNi·seed-1, and T3 = 1.6 µgNi·seed-1) were inoculated with P. pachyrhizi at the V4 growth stage. The ASR severity was evaluated 16 days after inoculation (DAI) and the chlorophyll (Chl) a fluorescence parameters at 8 and 16 DAI. The ASR severity decreased by 64 and 47% for treatments T2 and T3, respectively, in comparison to T1 treatment. The photosynthetic apparatus was negatively affected by ASR. The efficiency of the use of light by photosystem II decreased while the energy dissipated by nonregulated form increased in the infected leaflets. There was no significant difference for Chl a fluorescence parameters for T1, T2, and T3 treatments applied to inoculated plants probably due to the biotrophic lifestyle of P. pachyrhizi associated with lower ASR severity. In conclusion, the potential of using seeds with higher Ni content as a tool for ASR integrated management control is highlighted in this study.

ABSTRACT Nickel (Ni) was the latest element to have its nutritional essentiality recognized for plants (Brown et al. 1987). It is a component of various enzymes, including glyoxalases (family I), hydrogenases, superoxide dismutase and urease (Chen et al. 2009). Inadequate Ni supply promotes changes in the plant metabolism, including processes related to nitrogen metabolism, such as amino acids, urea and ureides metabolisms (Rodríguez-Jiménez et al. 2016; Bai et al. 2006). Legumes that are dependent on N2 fixation (e.g., soybean) have their process impaired by Ni deficiency, because this element is an essential catalytic cofactor of [NiFe]-hydrogenase, an enzyme found in some symbiotic bacteria that recycles the H2 produced by a side reaction of nitrogenase in root nodules formed by the plant-bacteria association (Cammack 1995; Bagyinka 2014). Moreover, Ni has shown the potential to control soybean diseases, such as powdery mildew (Barcelos et al. 2018) and Asian soybean rust (Einhardt et al. 2020a; 2020b).

ABSTRACT White mold, caused by Sclerotinia sclerotiorum, is one the most devastating disease on soybean worldwide. Considering the potential of phosphites to protect plants against different diseases, this study investigated the possibility of using potassium (K), calcium (Ca), and zinc (Zn) phosphites for white mold control in soybean. The contact effect of the phosphites on fungal mycelial growth was evaluated in vitro. In the greenhouse study, plants were inoculated with S. sclerotiorum at 48 h after being sprayed with water (control), K, Ca, and Zn phosphites by using an agar plug (0.8 cm2) containing fungal mycelia. Lesion area of white mold and chlorophyll (Chl) a fluorescence parameters were evaluated on the leaflets of plants at 96 h after inoculation. The Chl a parameters were also evaluated in noninoculated leaflets at the same time. Fungal mycelial growth was abundant in the absence of phosphites, but inhibited in the presence of the three phosphites indicating their direct effect. The lesion area in the leaflets of plants sprayed with K, Ca, and Zn phosphites were 90, 98, and 68% lower, respectively, compared to plants sprayed with water. The functionality of the photosynthetic apparatus was more preserved on the leaflets of plants sprayed with phosphites due to the lower lesions size, especially for the Ca phosphite. In conclusion, the K, Ca, and Zn phosphites were effective in reducing white mold symptoms mainly through a contact effect on the fungal mycelial growth.

ABSTRACT Considering the importance of silicon (Si) to increase rice resistance to blast, this study investigated the nutritional status of rice plants supplied with this element in response to Pyricularia oryzae infection. Plants were grown in nutrient solutions containing 0 and 2 mmol·L-1 of Si (referred to -Si and +Si plants, respectively). The area under blast progress curve decreased for +Si plants due to a significant increase of 714% on the foliar Si concentration in contrast to -Si plants. For +Si plants, the foliar N, P, K, Ca, Mg, Cu, and B concentrations were significantly lower in comparison to -Si plants. On infected plants, the foliar N, K, and Cu concentrations were significantly lower in comparison to noninfected ones. The foliar Zn, Fe, and Mn concentrations were significantly lower for -Si inoculated plants in comparison to -Si noninoculated ones. The foliar Mn and S concentrations were significantly lower for +Si inoculated plants in comparison to +Si noninoculated ones. The foliar Fe concentration was significantly lower for +Si inoculated plants in comparison to +Si noninoculated ones. Foliar Zn and Mn concentrations were significantly lower for +Si plants in comparison to -Si plants regardless of their inoculation with P. oryzae. Foliar Fe and S concentrations were significantly lower for +Si plants in comparison to -Si plants, respectively, for noninoculated and inoculated plants. Taken together, Si stood for itself in reducing blast symptoms without the need of high foliar concentrations of either macro or micronutrients that could affect plantgrowth.

The aim of the present study was to investigate the influence of tyrosine on the in vitro growth and the production of the betacyanin pigment in Alternanthera philoxeroides and A. tenella. Nodal segments were inoculated in MS medium containing different concentrations of tyrosine (0, 25, 50 and 75 μM), and the number of sprouts and buds, height, root length, fresh matter of shoots and roots and betacyanin content were evaluated. In A. philoxeroides , the highest production of betacyanin (51.30 mg 100 g-1 FM) was in the stems with the addition of approximately 45 μM tyrosine, while the increase in the leaves was proportional to the tyrosine concentration, and the best average was obtained with a tyrosine concentration of 75 μM (15.32 mg 100 g-1 FM). Higher tyrosine concentrations were deleterious to the growth of A. tenella plants, and a concentration of 75 μM was considered toxic. However, a tyrosine concentration of 50 μM benefitted betacyanin production, which reached 36.5 mg 100 g-1 FM in the plant shoots. These results showed the positive effect of tyrosine on the production of betacyanin in both species; however, application at high concentrations hampered the growth of Alternanthera plants.

Salinity is a limiting factor fot growth and development, since it affects several physiological processes in plants. This trial aimed to assess the levels of photosynthetic pigments, betacyanins, lipid peroxidation and activity of antioxidant enzymes in Alternanthera philoxeroides under salt stress. Plants originated from an in vitro culture were acclimatized and irrigated with sodium chloride (0, 200 and 400 mM) for 30 d. The experimental design was completely randomized with a 3×2 factorial arrangement of treatments: three concentrations of NaCl and two plant tissues (stems and leaves). The experimental data was subjected to an analysis of variance and means where compared using Tukey test (p≤0.05). The levels of chlorophylls a, chlorophylls b and total carotenoids presented similar responses, decreasing their values according to salt concentrations, while the chlorophyll a/b ratio of the plants that were submitted to the highest salt concentration presented a significant increase when compared to the control. Higher levels of betacyanin were observed on stems, when compared to the leaves, in the highest salt concentrations. On the leaves, there was a significant increase of lipid peroxidation and superoxide dismutase activity, whereas roots showed an increase of the enzymes catalase and ascorbate peroxidase. Salt stress caused greater degradation in the photosynthetic pigments, increment of betacyanin synthesis in stems, and damage to the cell membranes of the leaves. However, the increase of antioxidant enzymes activity stimulated the protective system against oxidative stress. It is concluded that Alternanthera philoxeroides (Mart.) Griseb. plants present reduction in levels of photosynthetic pigments, increased synthesis of betacyanins and increased activity of antioxidant enzymes in leaves and roots when exposed to salt stress.

La salinidad es un factor limitante para el crecimiento y el desarrollo, ya que afecta varios procesos fisiológicos en las plantas. Este estudio tuvo el objetivo de evaluar los niveles de pigmentos fotosintéticos, betacianinas, peroxidación lipídica y actividad de enzimas antioxidantes en Alternanthera philoxeroides bajo estrés salino. Las plantas se originaron de un cultivo in vitro y se aclimataron e irrigaron con cloruro de sodio (0, 200 y 400 mM) durante 30 d. El diseño experimental fue completamente aleatorio con un arreglo factorial 3×2 de los tratamientos: tres concentraciones de NaCl y dos tejidos vegetales (tallos y hojas). Los datos experimentales se sometieron a un análisis de varianza y las medias se compararon usando la prueba de Tukey (p≤0.05). Los niveles de clorofilas a, clorofilas b y carotenoides totales presentaron respuestas similares, disminuyeron sus valores con las concentraciones de sal, mientras que la relación de clorofila a/b de las plantas que se expusieron a la concentración mayor de sal presentó un incremento significativo respecto al control. Niveles mayores de betacianinas se observaron en los tallos, en comparación con las hojas, para las concentraciones de sal más altas. En las hojas hubo un aumento significativo de peroxidación lipídica y de actividad de superóxido dismutasa, mientras que las raíces mostraron un aumento en las enzimas catalasa y ascorbato peroxidasa. El estrés salino causó degradación mayor de los pigmentos fotosintéticos, un aumento en la síntesis de betacianinas en los tallos, y daño a las membranas celulares de las hojas. Sin embargo, el incremento de actividad de las enzimas antioxidantes estimuló el sistema protector contra el estrés oxidativo. Se concluye que las plantas de Alternanthera philoxeroides (Mart.) Griseb. presentan una reducción en los niveles de pigmentos fotosintéticos, mayor síntesis de betacianinas y mayor actividad de enzimas antioxidantes en las hojas y raíces cuando están expuestas a estrés salino.