Pattern of disease spread provides improved knowledge on how the pathogen introduces itself and interacts with environment in fields and expresses as a disease. It is especially significant when epidemiology of a disease, such as Rice False Smut (RFSm), is unclearly understood. Not reported before, this study attempted an analysis of spatial pattern of natural spread of RFSm in nine fields in an intensive rice ecosystem in Bangladesh. Both conventional and specialized statistical methods were applied in the analysis. Results show that the spread of the disease was not similar between and within the fields and even some fields were almost disease free. RFSm recorded aggregation in spaces in most of the fields, but the location of this aggregation differed between the fields. Symptom recorded on panicles in regenerated tillers from harvested main crop (otherwise known as ratoons). The disease tended to be prominent towards proximity of drainage channels. The probability of occurring one diseased tiller per hill was calculated as 73% and cumulative probability of four or less smut balls per diseased panicle as little over 60%. This study establishes soil as the absolute dominant source of initiation of the epidemic. The analysis did not find evidence of any long-or short-distance primary and/or secondary sources of infection. It is concluded that the disease management be directed specific to the fields at risk. It suggests development of a soil testing tool for quantifying inoculum potential in a field to ascertain the risk. With the discovery of symptom on ratoons, this study highlights the need for fresh thinking on identifying the pathway of entry of the pathogen into the plant.

Rice False Smut (RFSm) is presently an internationally important fungal disease of rice. While the Yield Loss (YL) from this disease is reported in many countries, there exists no tool to instantly estimate the YL by visual field inspection. This study developed a simple model, FLYER, for this purpose. The model is run by two inputs: (i) fraction of productive but diseased tillers in a field and (ii) averaged number of smut balls present in the diseased panicles. FLYER was developed using data from Bangladesh, India and Japan. The driving algorithm of the model, the yield reduction in a diseased panicle as a function of number of smut balls present in the panicle, was validated with additional data from Bangladesh and Japan. When tested with independent data from fields infected naturally by RFSm, FLYER closely estimated the Yield Loss (YL, %) against observed datasets from Bangladesh (Root Mean Squared Deviation (RMSD) = 1.15% YL), Egypt (RMSD = 1.65% YL) and India (RMSD = 1.68% YL). This model could contribute to rapid assessment of regional and variety-specific yield loss and strategic management of the disease on a field-by-field basis.

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A field experiment was carried out at Sonapur of Muradnagar upazilla in Cumilla district under the Debidwar MLT (Multi-Location Testing) site during the rabi season of 2013-15. The experiment was conducted in the Old Meghna Estuarine Floodplain (AEZ-19) soil. The experiment was laid out in randomized complete block design (RCBD) with 3 replications.The treatments were: T1= Soil Test Based (STB) Fertilizer dose (FRG 2012), T2= T1+ 15% STB, T3= T1+ 30% STB, T4= 80% STB from inorganic fertilizer + 20% STB from CD/PM, T5= Farmers’ Practice andT6= Control. Among the treatments, T4 gave the maximum seed yield (1385.56 kg ha-1) which was at par with T1, T3 and T2 treatments. The lowest seed yield (450.20 kg ha-1) was obtained from T6 (Control). Bangladesh Agron. J. 2018, 21(2): 67-71

Rice false smut (RFSm), considered as a minor importance, has become a serious disease in many rice growing areas of Bangladesh and other parts of the world. Many aspects of its epidemiology still remained unclear, notable the life cycle of RFSm pathogen, its infection site and the smut ball formation on infected panicles. Present research was undertaken to investigate the density and distribution of false smut balls on infected rice panicles aiding to understand on how severe the disease can be in a rice-ecosystem, on which position the smut balls form on infected panicles and likely yield reduction from such disease severity. This study included field observation of natural RFSm infection during 2014, 2015 and 2016, and simulated infection during 2015 in T. Aman rice in the experimental farm of the Bangladesh Rice Research Institute (BRRI), Gazipur, Bangladesh. While the number of smut balls reached as many as 136 (recorded in one panicle in 2015), the study shows there was 81, 54 and 30% probability that maximum of nine, three and only one smut ball would form, respectively. With the scenarios of density of smut ball formation in the study area, the yield loss was estimated as 0.15% for each 1% incidence level. The level of smut ball density varied between years; this severity was most likely influenced by low daily minimum temperature. In the natural observation 34.4, 53.9 and 11.7% of the smut balls were located at the base, mid and apex part of the infected panicles, respectively. When compared the balls of these three positions in relation to potential grain number, the proportion accounted for the base and mid remained almost similar, whereas the proportion in the apex was much lower. It is concluded that false smut balls predominantly form on the lower half of the infected rice panicles.

A farmer participatory research was conducted to determine the yield advantage of cleaned seeds over farmer-saved seeds in seven sites in Bangladesh in five cropping (three Boro and two transplant Aman) seasons. In each site, 30 participating farmers transplanted seedlings from cleaned seeds and their saved seeds of the same variety in adjacent plots in their fields. The results show a significantly higher grain yield in the cleaned seed than the farmer-saved seeds of 10.1% in Boro season and 11.3% in transplant (T) Aman season. The highest advantage in yield of cleaned seeds over farmer-saved seeds of 12.2% was observed in Barisal in Boro season, and 15.5% in Habiganj in T. Aman season. In the Boro season, significantly lower mean incidences of weeds below canopy, rice hispa, whiteheads, brown planthopper and bakanae were observed for cleaned seeds than for farmer-saved seeds. In the T. Aman season, significantly lower mean incidences of deadheart, whiteheads, gall midge, green leafhopper, other defoliators, sheath blight, sheath rot, and kernel smut were observed for cleaned seeds than for farmer-saved seeds. This indicates that using cleaned rice seeds increased grain yield, enhanced crop growth and also reduced damage from weeds, insect pests and diseases.

Rice false smut (RFSm) is a disease of interest globally and in Bangladesh. Its occurrence and spread have drawn attention since 2010 in the country. While many reports are available on the yield loss from the disease, little is known of its effect on grain quality. Besides, there has been no information on how RFSm affects the seed quality with respect to germination. This study attempted evaluation of seed germination and grain quality of rice as affected by false smut disease. Three years’ study provided strong indication of inferior milling outturn and head rice yield in RFSm contaminated seeds. Results further revealed reduced amylose content and increased protein content in the contaminated seeds. Tendency in reduced seed germination, and less cooking time was observed in RFSm contaminated seeds. Future research is suggested to fully understand those causations. Bangladesh Rice j. 2018, 22(1): 1-7

Rice false smut has become an emerging disease across the world. Its incidence has become serious in Bangladesh during T. Aman season in the last five years. However, the status of the disease in farmer's field has not been estimated in this country. This study included a survey of 90 fields in four unions of Natore district during ripening stage of T. Aman rice of 2015 in order to estimate the disease incidence, number of smut balls per infected panicle and yield loss, and to ascertain effectiveness of farmer's unregistered foliar fungicide application. The results show that across the fields, disease incidence, number of smut balls per infected panicle and yield loss were 8.06±2.02%, 2.88±0.17 and 0.72±0.18% (± is 95% confidence interval), respectively. Disease incidence (18.71±5.18%), number of smut balls per infected panicle (3.51±0.39) and yield loss (1.75±0.38%) was the highest in Ramananda Khajura union compared to the other three unions surveyed. Among the varieties, BRRI dhan49 incurred the highest disease incidence (18.71±5.18%). The number of smut balls per infected panicle (3.51±0.39) and yield loss (1.75±0.38%) were also the highest in this variety. The crops which flowered during mid October to early November showed significantly higher disease incidence than early flowering crops. Application of unregistered foliar fungicides tended to have reduced the disease, but did not show significant difference with 'no fungicide application'. It is concluded that the strategic management of the disease may be directed to the specific areas of the fields where there is a history of the disease through manipulating genotypes and transplanting time. Farmers should be cautious on adopting chemical option as there is no registered fungicide yet in Bangladesh for tactical management of the disease.