Rice brown spot (BS) is a chronic disease that affects millions of hectares of rice every growing season, grown by some of the most resource-poor farmers. Despite its widespread occurrence and impact, much still needs to be understood about BS. Reported yield losses in relative terms vary widely from 4 to 52 %. However, accurate, systematic estimates are lacking. BS is conventionally perceived as a secondary problem that reflects rice crops that experience physiological stresses, e.g. drought and poor soil fertility, rather than a true infectious disease. Much remains to be understood about the mechanisms leading to epidemics and crop losses. Quantitative and qualitative knowledge gaps exist in our understanding of the epidemiological processes, sources of resistance and biocontrol methods. In this review we identify several of these gaps, which if filled, could lead to a strong impact on the management of brown spot. We also use the architecture of a simulation model to position and prioritize these knowledge gaps, assess the epidemiological consequences of disease management options on
The laboratory incubation experiment was accomplished to study the effect of incubation periods on the extractable Fluoride (F) and Phosphorous (P) in soil at different exchangeable sodium percentage (ESP) levels. The soils of different ESP levels (30, 45 and 60) were prepared by applying different amount of sodium bicarbonate dissolved in distilled water to the calculated volume of saturation percentage of the soil. The observed ESP of the prepared soil was 27.1, 43.7 and 54.9. Incubation studies were conducted with fluoride levels ranging from 40 to 160 mg/kg and phosphorus levels from 12.5 to 50 mg/ kg with incubation periods of 1, 3, 7, 14, 21, 28 and 35 days at temperature of 25±2 0 C. Moisture was maintained at field capacity by addition of distilled water. The results showed that the extractability of fluoride in soil increased with increasing levels of F and P application along with increased ESP. The increase was 100 percent at ESP 54.9 compared to ESP 6.2 at F level of 160 mg/ kg at 1st day of incubation period. Similarly, Olsen's extractable phosphorus in soil increased with increasing levels of F, P and ESP. It increased by 66 percent at ESP 54.9 compared to ESP 6.2 at P level of 50 mg/kg at 1 st day of incubation period. However, extractability of both F and P decreased with increase in incubation periods. Fluoride extractability decreased by 65 percent at ESP 6.2 and 25 percent at ESP 54.9 with increasing days from 1 st to 35 th day of incubation period. Olsen's extractable phosphorus decreased by 37 percent at ESP 6.2 and 48 percent at ESP with increasing days from 1 st to 35 th day of incubation period.
Surveys were carried out in eight districts of Jharkhand. Hill infestation, tiller infestation and infected grains with false smut of rice were recorded higher in hybrid rice in comparison to none hybrid (HYV) rice in all surveyed areas of Jharkhand. Hill infestation with false smut of rice ranged from 3.8 to 31.7 % in twenty one rice cultivars. Highest tiller infestation with false smut was recorded in Arize 6444 (24.8%), followed by PAC 801 (22.5%), KRH 2 (22.3%), 25P25 (21.7%) and PHB 71 (20.3%). Highest false smut infected grains/panicle was recorded in PAC 801 (8.6) followed by Arize 6444 (8.2). Application of higher level of N-fertilizer in rice recorded higher tiller infestation of false smut of rice, higher number of false smut infected grains /panicle and higher hill infestation of false smut of rice during 2016 and 2017 crop seasons. Closer spacing in rice recorded higher tiller infestation of false smut of rice, higher number of false smut infected grains/ panicle and higher hill infestation of false smut of rice in all three levels Nfertilizers i.e., 90, 120 and 150 Kg N ha -1 during above two crop seasons. False smut symptom was observed on all three levels of nitrogen having five spacing of rice in both 2014 and 2015 crop seasons. Highest mean grain yield of 78.5 q ha -1 was recorded in plots where N-fertilizer was applied @120 Kg ha -1 and spacing of rice was 25 cm X 25 cm, this treatment also recorded mean tiller infestation of 7.8%, lowest mean infected grains/ panicle of 6.3 and lowest mean hill infestation of 11.7%. This treatment was at par with treatment having N-fertilizers was applied @ 120 Kg ha -1 and spacing of 20 cm X 20 cm, which recorded mean grain yield of 77.0 q ha -1 , mean tiller infestation of 9.1% and mean hill infestation of 6.6%.
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