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.
