Microscopic Aspects of Silicon-Mediated Rice Resistance to Leaf Scald

Abstract

This study investigated the effect of silicon (Si) on the potentiation of rice resistance against leaf scald at the microscopic level. Rice plants ('Primavera') were grown in a nutrient solution containing 0 (-Si) or 2 mM (+Si) Si. The foliar Si concentration of the +Si plants (3.6 dag/kg) increased in comparison with the -Si plants (0.3 dag/kg). An X-ray microanalysis revealed that the leaf tissue of +Si plants infected with Microdochium oryzae had higher peaks and deposition of insoluble Si than that of -Si plants. The high foliar Si concentration for the +Si plants reduced the expansion of leaf scald lesions. Scanning electron microscopy revealed that fungal hyphae and appressorium-like structures of M. oryzae were more abundant in the leaf surface of -Si plants relative to +Si plants. At both histopathological and ultrastructural levels, fungal hyphae grew abundantly into the leaf tissue of -Si plants. By contrast, rice cell walls were rarely degraded and fungal hyphae were often surrounded by amorphous granular material in the leaf tissue of +Si plants. Conidiophores emerged from stomata 36 h after fungal penetration, and conidia were noticed inside the leaf tissue of the -Si plants in great abundance. The collective results of the present study showed a high concentration and deposition of Si and a considerable deposition of phenolic-like compounds in the leaf tissue of +Si plants. These results indicate that the potentiation of the phenylpropanoid pathway in these plants supplied with Si was favorable for the increase in rice resistance to leaf scald.

Association of the Production of Phenylpropanoid Compounds at the Infection Sites of Corynespora cassiicola with Soybean Resistance against Target Spot

“…; Araujo et al. ,b, , ). Most cells on the leaves of plants from cultivar Fundacep 59 reacted against C. cassiicola infection by accumulating phenolic‐like compounds, which probably contributed to the dead appearance of many fungal hyphae as well as greater maintenance of cell integrity due to their possible antimicrobial activity.…”

“…Initial events in the pathogenesis of certain pathogens on the surface of their hosts can be distinct according to the levels of resistance against the pathogens; this can therefore result in different levels of disease severity (Araujo et al. ,c, ). The apparent abundance of trichomes on the adaxial leaf surface of plants from cultivar Fundacep 59 in comparison with cultivar TMG 132 may have impaired the deposition and germination of the conidia of C. cassiicola .…”

“…; Araujo et al. , , ;). When the specimen stained with toluidine blue is viewed under the microscope, different cell components produce different colours: DNA is bluish green, RNA is violet, the middle lamella is red, non‐lignified cell walls and soluble phenolic compounds are red‐violet, blue‐violet, blue or purple and polymerized phenolics such as lignin are green or bluish green.…”

“…; Araujo et al. , , ). Deposition of lignin and flavonoids has been histochemically detected in the roots of banana plants and in the leaves of rice plants supplied with silicon and infected by Fusarium oxysporum f.sp.…”

“…At the microscopic level, several studies have demonstrated differences of defence responses between resistant and susceptible plants during the infection process of fungal pathogens (Rodrigues et al 2003;Araujo et al 2014aAraujo et al ,b,c, 2015Araujo et al , 2016Fortunato et al 2014;Silva et al 2015). Germinated conidia of Colletotrichum gloeosporioides showed different patterns of appressoria formation and germ tube growth on the leaves of apple cultivars that differed in their levels of resistance to Glomerella leaf spot (Araujo et al 2014c).…”