Identification of Resistant Germplasm to Rice Blast under Silicon Amendment in Uganda

Rice blast caused by Magnaporthe grisea is one of the most serious diseases of rice, causing yield losses of 50 – 100% in susceptible varieties worldwide. Durable host resistance has been hard to achieve given large pathogen diversity and capacity of pathogen to mutate. It has been suggested that silicon enhances durable resistance in partially resistant genotypes. A study was conducted to evaluate rice genotypes for their reaction to M. grisea under silicon amendments and to detect genotypes with high silicon uptake. Sixty-seven genotypes were evaluated for their reaction to Magnaporthe grisea under silicon amendments in a CRD in three replications in a screen house. Seeds were planted in soil amended with silica gel at the rate of 0, 29, and 58 g per 180 g of soil. Genotypes were inoculated with a virulent strain of Magnaporthe grisea (Namulonge isolate) 21 days after planting. Seven plants were inoculated per genotype. Data were taken on lesion size induced by blast one week after inoculation and, interpreted from 9 to 0. Data were also taken on leaf blast severity and used to compute area under disease progress curve (AUDPC). Twenty-four genotypes were highly resistant (HR), twenty - two were resistant (R), fourteen were moderately resistance (MR), four were moderately susceptible (MS) and three were susceptible (S). Silicon concentration significantly (P <.001) impacted on the reaction of genotypes to blast. The interaction of genotypes with silicon was also highly significant (P <.001). AUDPC was significantly influenced by silicon concentration (P = 0.008). The genotypes that consistently showed resistance to rice blast disease were recommended to similar conditions. The sixty-seven genotypes were screened for the capacity to absorb silicon. Twenty-day old seedlings were placed into 50 ml plastic bottles containing one-half concentration of Kimura B solution, adjusted with 0, 5, 10 and 15 mM silicon respectively. Each bottle was wrapped with an opaque plastic membrane for 12 hours after Si application. 0.9 ml of silicon uptake solution was drawn from each bottle and silicon concentration determined. Final silicon uptake ability readings were highly significant among genotypes. The leaf blast reaction of the genotypes under silicon amendment was found to be directly proportional to their silicon uptake ability which in turn increased with the increasing amount silicon solution absorbed by the plant, from 5, through 10 to 15 Mm/L. Significant correlations of Si uptake abilities to blast disease reactions and area under disease progresses were found in this study.