Abstract
It is well documented that slag-based silicon fertilizers have beneficial effects on the growth and disease resistance of rice. However, their effects vary greatly with sources of slag and are closely related to availability of silicon (Si) in these materials. To date, few researches have been done to compare the differences in plant performance and disease resistance between different slag-based silicon fertilizers applied at the same rate of plant-available Si. In the present study both steel and iron slags were chosen to investigate their effects on rice growth and disease resistance under greenhouse conditions. Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the effects of slags on ultrastructural changes in leaves of rice naturally infected by Bipolaris oryaze, the causal agent of brown spot. The results showed that both slag-based Si fertilizers tested significantly increased rice growth and yield, but decreased brown spot incidence, with steel slag showing a stronger effect than iron slag. The results of SEM analysis showed that application of slags led to more pronounced cell silicification in rice leaves, more silica cells, and more pronounced and larger papilla as well. The results of TEM analysis showed that mesophyll cells of slag-untreated rice leaf were disorganized, with colonization of the fungus (Bipolaris oryzae), including chloroplast degradation and cell wall alterations. The application of slag maintained mesophyll cells relatively intact and increased the thickness of silicon layer. It can be concluded that applying slag-based fertilizer to Si-deficient paddy soil is necessary for improving both rice productivity and brown spot resistance. The immobile silicon deposited in host cell walls and papillae sites is the first physical barrier for fungal penetration, while the soluble Si in the cytoplasm enhances physiological or induced resistance to fungal colonization.
Highlights
Silicon (Si) is the second most abundant element in soils [1,2]
Dry weight of leaf and stem showed no significant difference between the two Si fertilizers tested, but Si fertilizer H produced significantly more grain weight than Si fertilizer Q
Application of both Si fertilizers significantly increased the Si concentration in leaf, stem and grain compared with the Si0 treatment
Summary
Silicon (Si) is the second most abundant element in soils [1,2]. Rice (Oryza sativa L.) is the second most widely grown crop in the world, and the major staple food for more than half of the world’s population [8,9]. In tropical and subtropical areas, because of heavy desilication-aluminization arising from high temperature and rainfall, plant- available Si is low in these highly-weathered soils [11]. Repeated mono-cropping with rice may greatly decrease plant-available Si in soil. It is estimated that producing a total rice grain yield of 5000 kg ha will remove Si at 230–470 kg ha from the soil [5], and Si may become a yield-limiting element for rice production [12,13,14]. It maybe is necessary to provide exogenous Si fertilizer for an economic and sustainable rice production system [15,16,17,18]
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