Effect of Nitrogen, Silicon, Rice By-product and Fungicide for Management of Rice Blast Disease in Mwea Irrigation Scheme of Kenya Catherine

Abstract

Rice (Oryza sativa L) is a staple food for nearly-half of the world population contributing over 20% of total world calorie intake. In Kenya it is the third most important cereal after maize and wheat. Basmati 370 is the most preferred variety but highly susceptible to rice blast disease. Rice blast, caused by Pyricularia oryzae is one of the most important rice disease causing yield loss of 70-80%. A study was carried out in Mwea Agricultural Development Centre (MIAD) to determine the effect of fertilization with nitrogen, and silicon, application of rice by-product and fungicide for the management of rice blast. Soil and plant samples were collected from field that had infected and non-infected plants and analyzed for silicon and nitrogen levels. The effect of nitrogen and silicon on disease infection and yield of rice was tested using four levels of silicon fertilizer (0, 500, 1000, 1500kg Si/ha) and nitrogen fertilizers (0, 40, 80 120kg N/ha). Each treatment was replicated four times. The experiment was laid out in split plot design with fertilizer type as main plot and fertilizer levels as sub-plot factor. Data collected comprised of disease severity score, productive tillers, number of panicles, number of filled grains, seed weight and biomass. To determine the effect of different sources of silicon from rice by-products and commercial silicate on infection of rice by Pyricularia oryzae, calcium silicate (5000Kg/ha), rice straw (2ton/ha), rice husk ash (0.7tons/ha) and straw ash (0.6tons/ha). Basal fertilizers were added as recommended at 30 Kg K2O/ha, 58 KgP2O5 /ha and 80 KgN which was applied as a top dressing in two splits. Inoculums‟ of Pyricularia oryzae (4 × 105 conidia/ ml) was used to infect the rice plants and panicle blast infection was assessed using the IRRI standard. This xvii experiment was laid in a Complete Randomized Design (CRD). To determine the effect of selected chemical fungicides on in-vitro mycelial inhibition of Pyricularia oryzae, four chemical fungicides (Azoxystrobin 250 CS, Thiophanatemethyl, Hexaconazole and Carbendazim) commonly used by farmers were tested. Each fungicide was tested at three concentrations to determine the effectiveness of chemical fungicides in control of rice blast. The assessment was carried out by in-vitro bioassays at ambient temperature (250C). The efficacy of the fungicide was assessed by measuring the inhibition zones across a nine-mm Petri dish. Data in all the experiments was analyzed by Analysis of variance (ANOVA) using Statistical Analysis System (SAS) statistical package version 8.1 and means separations using least significance difference (LSD) at 5%. Results indicated significance differences among the infected and non-infected fields with nitrogen level being high in the rice blast infected field than in non-infected field in both 0-15 and 15-30cm depth. Silicon level was lower in the rice blast infected field at the two depth (0-15 and 15-30cm) than in non-infected. However highest concentration of silicon and nitrogen was at 0-15cm depth. Similarly infected plants showed higher nitrogen concentration while silicon was higher in the non-infected tissues. There was significant differences (P<0.05) in response of nitrogen and silicon in both yield and control of rice blast disease. The interaction between nitrogen and silicon was effective at 80KgN/ha and 1000 Si Kg/ha in both yield and in management of rice blast disease. Calcium silicate and the rice by products were significantly different in disease management but it was not different rice yield from the husk ash. There were significant differences (P<0.05) in mycelial inhibition of P. oryzae among the four fungicides. Carbendazim xviii and Thiophanate Methyl 50% w/v were effective at the highest and intermediate concentrations (2 and 3mls/lt) while Hexacanazole was effective at concentration (18.75mls/lt). The study has revealed that nitrogen at 80kg/ha and silicon at 1000kg/ha were effective in enhancing rice yield and management of rice blast. Carbendazim and Thiophanate Methyl 50% w/v were the most effective fungicides in the control of rice blast at 2mls/lit.