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Effect of Rice Growth Stages and Silicon on Sheath Blight Development

First author: University of Florida-IFAS, Department of Plant Pathology, Gainesville 32611; second author: Department of Plant Pathology, Universidade Federal de Viçosa, Departamento de Fitopatologia, Viçosa, MG, Brazil, 36570; third author: University of Florida-IFAS, Everglades Research & Education Center, Belle Glade 33430; fourth author: Centro Nacional de Pesquisa de Arroz e Feijão, Caixa Postal 179, Santo Antônio de Goiás, GO, Brazil, 75375; and fifth author: Universidade Federal de Uberlândia, Instituto de Ciências Agrárias, Caixa Postal 593, Uberlândia, MG, Brazil, 38400

The objective of this study was to determine the effect of silicon (Si) and rice growth stages on tissue susceptibility to sheath blight (Rhizoctonia solani Kühn) under controlled conditions. Rice plants (cv. Rio Formoso) were grown in pots containing low-Si soil amended with Si at 0, 0.48, 0.96, 1.44, and 1.92 g pot^-1 and inoculated with R. solani at the following days after emergence: 45 (four-leaf stage), 65 (eight-leaf stage), 85 (tillering), 117 (booting), and 130 (panicle exsertion). For plants inoculated with R. solani at all growth stages, Si concentration in straw increased as rate of Si increased from 0 to 1.92 g pot^-1. Concentration of calcium in the straw did not differ among plant growth stages. Although incubation period was not affected by the amount of Si added to the soil, this variable was shorter at booting and panicle exsertion stages. As the rates of Si increased in the soil, the total number of sheath blight lesions on sheaths and total area under the relative lesion extension curve decreased at all plant growth stages. The severity of sheath blight was lower at booting and panicle exsertion stages as the rates of Si increased in the soil. In general, plants grown in Si-nonamended pots and inoculated with R. solani were more vulnerable to infection at all growth stages, but especially at 45 days after emergence. Plant dry weights for inoculated plants increased as the Si rates increased from 0 to 1.92 g pot^-1. The greatest dry weight increases occurred for plants inoculated at booting and panicle exsertion stages. Si fertilization is a promising method for controlling sheath blight in areas where soil is Si deficient and when cultivars that exhibit an acceptable level of resistance to sheath blight are not available for commercial use.

Additional keywords: calcium silicate slag, host resistance, Oryzae sativa, Rhizoctonia solani.