Silicon enhances resistance to Alternaria blight leaf spot disease in radish plants (Raphanus sativus L).

Abstract

The family Brassicaceae comprises valuable and economically important species for human health and nutrition such as preserved or fresh vegetables, oilseeds, and condiments. Among those species, one of the prominent types of vegetables is radish (Raphanus sativus L.). However, the sustainable production of radishes is highly threatened by many biotic stresses, Alternaria blight leaf spot disease is one of the most prominent diseases caused by a necrotrophic fungal pathogen Alternaria brassicae. The onset of this disease results in the development of dark brown to black necrotic lesions on leaves and older leaf stems, characterized by concentric rings frequently encircled by a chlorotic halo. This ailment significantly impairs radish quality and yield by disrupting the photosynthetic mechanism. Silicon (Si) is a beneficial element that has the potential to stimulate disease resistance in plants. In this study, liquid silicon (0- 1.5g/100mL/plant) was exogenously applied to three-week-old radish plants grown in pots with sterilized coir for six weeks with 7-day intervals and contaminations between treatments were controlled by having space between pots and without water draining out. Control plants were treated only with the nutrient solution. Plants were grown in a controlled environment with 25– 35 ºC temperature and 65–75% relative humidity. A. brassicae fungal strain was isolated and identified morphologically by visualizing it under microscopes with identical spore shapes. After identification, pure cultures were developed for inoculation by subculturing. Same-size (1 cm × 1 cm) agar pieces with isolated fungus were used to inoculate 45-day silicon-treated radish leaves under in-vitro conditions by conducting a detached leaf assay. During the assay, the lesion areas were observed to determine the virulence of the pathogen, and the area was measured using IMAGE J software. A. brassicae was able to infect all the silicon-treated leaves and control leaves after 24 hours post-inoculation (hpi). The level of virulence of the pathogen was identified by conducting a confirmatory experiment as Trypan Blue (TB) staining. According to the results, infection was more severe in control leaves compared to silicon-treated leaves and the lesion area was higher in control leaves (179.08 ± 6.8 cm2) than in silicon-treated leaves, they showed lower lesion areas such as 186.38 ± 3 cm2, 67.31 ± 1.6 cm2, 56.5 ± 3.8 cm2 (p <0.01). Data was statistically analyzed by performing One-way ANOVA. According to the results, the lowest infected area was observed in leaves treated with a 1.5 g/100mL/plant) liquid silicon.