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Weather Condition, Seasonal Variation and Ball Development Pattern in Relation to Rice False Smut Disease in Bangladesh

B Nessa*
Department of Plant Pathology and Seed Science, Sylhet Agricultural University, Sylhet 3100, Bangladesh

M U Salam
Freelance Consultant (Agricultural Research, Development and Modelling), C1 (Dishari-10), BRRI Residential Area, BRRI, Gazipur 1701

A H M M Haque
Department of Plant Pathology and Seed Science, Sylhet Agricultural University, Sylhet 3100, Bangladesh

M A Kashem
Department of Soil Science, Sylhet Agricultural University, Sylhet 3100

M S Kabir
Bangladesh Rice Research Institute (BRRI), Gazipur1701, Bangladesh

Abstract/ Executive Summary:

Rice false smut (RFSm) is an international disease. The effect of the disease has become seriously evident in Bangladesh since 2010. The disease is predominant in the country in the ‘T. Aman’ rice growing season. Its occurrence in other rice growing seasons not well studied and recorded. Information on driving weather variable(s) causing the disease epidemic is scanty and not ground-truthed. This study, conducted in the experimental farm of the Bangladesh Rice Research Institute, Gazipur,Bangladesh, attempted to fill those information gaps. The association of disease incidence and weather parameters such as relative humidity, cloud hour and rainfall, was inconsistence except for the daily average temperature. High disease incidence occurred when the average temperature during panicle emergence period ranged between 22-27°C; any temperature below or above the range linearly decreased the disease incidence. RFSm disease was recorded in the study area in all the months, except for in February and March. The distribution in the incidence of disease in the three rice growing seasons followed the order of ‘T. Aman’ > ‘Aus’ > ‘Boro’; it was~six times less in ‘Aus’ and~eight times less in ‘Boro’ season, compared to ‘T. Aman’ season. New balls formed on infected panicles in batch by batch. High number of such batches formed in ‘T. Aman’ season. The final status of the disease in an infected crop was the accumulation of incidence of the disease in each batch. This study provided key epidemiology on the development of RFSm in nature and it is concluded such information on the disease under local conditions would be the key to designing management options.

Keywords: Rice false smut, Disease incidence, Epidemic, Pattern of smut ball development, Weather variables, Seasonal variation, Ustilaginoidea virens, Villosiclava virens

Location: Bangladesh Rice Research Institute (BRRI), Gazipur, Bangladesh

Start Date:

End Date:

Program Area: Pest Management

Commodity: Diseases, Rice

Objectives:

This research was undertaken to investigate the weather driver(s) during panicle emergence causing the disease epidemic, the relative incidence of false smut disease in three rice growing seasons of Bangladesh and the sequence of infection and/or disease appearance in infected panicles.

Methodology:

The study was carried out in the experimental farm of the Bangladesh Rice Research Institute (BRRI), Gazipur, Bangladesh, located at 23°5’N latitude, 90°2’ E longitude. This farm has built up as an intensive rice-ecosystem in the last 40 years by growing three rice crops annually in 192 fields spread over 40.48 hectare area (Nessa, 2017). The recorded rice false smut disease incidence (DI) was calculated as follows. DI = [(Number of diseased panicles) / (total number of panicles)] × 100 Data for relating disease incidence and weather variables The disease incidence of 46 fields in the study area was monitored at different time of the year during 2014, 2015 and 2016. Historically, 16 fields had high, 12 had moderate and 18 had low disease pressure.Disease incidence and panicle emergence time (50% flowering)in those fields were recorded.Monitoring of the disease incidence in ‘Boro’, ‘Aus’ and ‘T. Aman’ riceThe disease incidence was visually monitored weekly at the ripening stage (post-panicle emergence to late maturity) of rice crops during September 2014 through to September 2017 by scouting across the fields in the experimental farm of the Bangladesh Rice Research Institute (BRRI), Gazipur, Bangladesh, located at 23°59’ Nl altitude, 90°24’E longitude. The RFSm incidence was assessed in the fields which showed apparently high infection. The sample size (number of panicles) varied between 158 and 9648; the size depended on the prevalence of the disease. Batch by batch smut ball formation The sequence of new smut ball formation (each sequence was termed as a ‘batch’) was studied during T. Aman 2015. The test variety ‘BRRI dhan49’ was transplanted on 19 July in a 30.5 m × 2.5 m section of a field in the ‘West Byed’ section of the experimental site where the disease pressure was historically high. The plot was sub-divided into three sections, each represented a replication. The hills in the main crops were harvested at maturity by manually cutting the tillers at 40-60 cm height and then the ratoons (regenerated tillers) were allowed to grow. No additional crop management practices were applied for ratoons, except for maintaining a water level of 2 to 3 cm through irrigation. The new smut balls, by batches, were counted on ratoons as those appeared beginning on 17 November and ending on 5 January (2016). Altogether, 8 batches were recorded and the number of panicles observed was 485, 464, 407, 539, 412, 431, 501, and 573, respectively for batches 1 through to 8.In addition, during ‘Aus’ 2017, the sequence of new smut ball formation was monitored on testing breeding lines in the research field of Biotechnology Division in the experimental site. This location was purposively selected as the disease pressure had been historically high. This monitoring was carried out weekly during August to September. On each visit, about 10000 panicles were inspected.Statistical analysis For developing the relationship between weather variables and RFSm incidence, daily weather data from Plant Physiology Division of BRRI were collected. Moving average (the day and post two days of panicle emergence) of each of the four weather variables, average temperature°C, relative humidity (%), cloud hour and total rainfall (mm), were summarized for each data-point (46 samples). The relationship between each of the weather variables and the disease incidence was analysed through X:Y graph. Data from the high disease pressure field are presented in this manuscript.The observation of the disease incidence was expressed as the mean and 95% confidence intervals (CI) of the fields assessed. The results of the batch-by-batch smut ball formation were summarized in two ways: (i) the incidence of the disease as mean and 95% CI of three replicates; and (ii) cumulative percentage of disease incidence at three panicle emergence times–15 November, 30 November and 15 December. The CI was calculated using the in-built formula in MS Excel.

Source of Information: Bangladesh Rice J. 22 (1): 57-64, 2018

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

RFSm has the potential to infect rice year-round in Bangladesh, although it is still largely dominant in T. Aman season. Relatively high incidence of the disease away from T. Aman such as in 2017, warrants investigation on whether variability in weather pattern responsible for altering the pattern of disease incidence in Boro and Aus seasons. The association of temperature and each batch of smut ball formation to be further investigated to ascertain the exact duration of the temperature required for symptom development.

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