Abstract
Rice false smut (RFS) disease has emerged as one of the main diseases in most of the major rice- growing countries of the world. Management options for controlling RFS disease are not yet clear as little research has been done in this regard in Bangladesh. This study aimed to provide a better understanding and to develop an integrated management approach for RFS disease at the field level for successful rice production. To fulfill these objectives two intensive field surveys in Tanore Upazila of Rajshahi during T. Aman seasons of 2013 and 2014, in vitro experiments on the germination ability of chlamydospores of RFS disease pathogen, field experiments on varietal screening, field applications of fungicides, botanicals and mineral nutrients for RFS disease management were carried out at 3 locations viz. BRRI Headquarters, Gazipur, BRRI regional station, Rajshahi and farmers' field at Tanore Upazila of Rajshahi district. Survey studies identified the application of overdose of urea, cultivation of susceptible rice varieties, early seeding (1st week of June), light-textured soil, and rainfall at flowering time (Mid October) as congenial environment for the RFS disease outbreak. Rice was highly infected with the disease ranging from 10-60% panicle infection in the surveyed area, and disease incidence was the highest in BRRI dhan49 (50- 60%) followed by Swarna (40-50%) and Binadhan-7 (10-15% ). Chlamydospores' germination of RFS pathogen was favored in the pH ranges from 6.0-7.0 and with increase of glucose concentration from 0.10-1.00% in the growth medium. The minimum germination of chlamydospores was observed at 50°C, and fungicide Tilt (Propiconazole) 500 ppm inhibited the chlamydospores' germination significantly. Six rice varieties viz. BRRI dhan49, BRRI dhan56, BRRI dhan57, Binadhan-7, IR28 and Swarna having differences in growth durations as well as flowering time were evaluated as test varieties against RFS. The disease incidence of RFS was found in the sequence of BRRI dhan49 (21.85%) > Binadhan-7 (21.15% ) > Swarna (20.51%) > BRRI dhan56 (20.51%) > BRRI dhan57 (15.35%) > IR28 (13.65%), while the disease severity index was in the order of Binadhan-7 (101.52%) > Swarna (88.24%) > BRRI dhan56 (88.19%) > BRRI dhan49 (72.10%) > BRRI dhan57 (30.07%) > IR28 (27.30% ). As regards to yield, the variety IR28 produced the maximum grain yield (4.65 t/ha) followed by BRRI dhan49 (4.23 t/ha), Swarna (4.20 t/ha), BRRI dhan56 (4.06 t/ha), BRRI dhan57 (3.72 t/ha) and Binadhan-7 (3.68 t/ha). Twelve commonly-used fungicide groups were evaluated against RFS disease under field conditions, and 'Tilt 250EC' (Propiconazole) was found as the most effective that reduced 70.66%, 54.57% and 56.93% RFS disease incidence over control at BRRI Headquarters, BRRI regional station in Rajshahi and farmers field at Tanore Upazila of Rajshahi, respectively. Two botanicals such as Neem oil and Garlic extract were also evaluated against RFS disease outbreak under field conditions and the obtained results were not satisfactory. As regards to nutrient management, RFS disease infestation was assessed under field conditions due to added additional NPKS with recommended doses of fertilizers at three different locations during T. Aman season using BRRI dhan49 as test cultivar. Rice false smut disease incidence and severity were increased significantly with the additional application of N with recommended doses of fertilizers whereas both were significantly decreased with the additional application of K and S. Finally, the study concluded that early seeding (1st week of June) of BRRI dhan49, BRRI dhan56, and Swarna should not be recommended for cultivation at the disease-prone areas of Bangladesh. If congenial weather prevails, the additional application of MoP and gypsum @ 37.5 kg/ha as top-dressing at the vegetative stage of rice and spraying of 'Tilt 250EC' at the recommended dose can be used to minimize the RFS disease infestation.