EVALUATION OF SOME IMPORTED HYBRID BORO RICE VARIETIES AGAINST MAJOR DISEASES UNDER NATURAL EPIPHYTIC CONDITIONS

Abstract

An investigation was carried out to evaluate imported hybrid rice varieties against major diseases under natural epiphytic conditions of Bangladesh during the boro season of 2008-09 at Sher-e-Bangia Agricultural University research farm. Fifteen hybrids (13 imported, 2 local) viz. Hira-I, Hira-2, ACI-l, Surma-I, Tal-l, Modhumoti-2, Krishan-2, Sonar Bangla-6, Richer-I 0 I, Moyna, Tia, Tinpata, Aloron , BRRI hybrid dhan-I, BRRI hybrid dhan-2 and 2 HYV check varieties viz. BRRI dhan ..28 and BRRI dhan-29 were evaluated regarding disease incidence and severity at 3 stages and the effect of diseases on yield and yield contributing characters. Six field diseases viz. brown leaf spot (Bipolaris oryzae), leaf blast (Pyricularia grisea), sheath blight (Rhizoctonia solani), BLB (Xanthomonas campestris pv. oryzae), narrow brown spot (Cercospora oryzae), and altemaria leaf spot (Alternaria tenuissima) were recorded and identified. The incidence and severity of diseases varied significantly from one another. The disease incidence and severity of brown spot at maturity stage were recorded from 15.51% to 25.85% and 0.64 to 4.15 (0-9 scale), respectively where Him-2 and ACI-I varieties showed good performance against the disease. In case of leaf blast, the disease incidence and severity ranged from 8.82% to 21.28% and 1.01 to 6.21 (0-9 scale), respectively at maturity stage where Him-2 showed the lowest incidence (8.82%) and severity (1.01). Richer-lot showed the highest incidence (21.28%) and severity (6.21). Disease incidence and severity of sheath blight varied from 9.27% to 25.82% and 1.52 to 8.74 (0-9 scale), respectively at maturity stage where Hira-I, Hira-2 and ACI-l showed better result against the disease. In case of BLB, the disease incidence and severity ranged from 13.28% to 28.92% and 1.21 to 8.72 (0-9 scale), respectively at maturity stage where TajI, Krishan-2, Aloron and Moyna were severely affected by this disease. In case of narrow brown leaf spot, the disease incidence and severity ranged from 6.27% to 12.23% and 1.10 to 5.84 (0-9 scale), respectively at maturity stage where, the highest incidence (12.23%) and severity (5.84) was recorded on Modhumoti-2 and the lowest incidence (6.27%) and severity (1.10) was observed on ACI-1. Disease incidence and severity of altemaria leaf spot also varied from 13.27% to 32.12% and 1.42 to 3.00 (0-9 scale), respectively at maturity stage. The highest growth and yield contributing characters recorded on ACI-l, Hira-I and Him-2 considering plant height, panicle length, effective panicle and filled grain. Grain yield ranged from 4.50 tJha to 10.77 tIha. In case of hybrids, the highest grain yield (10.77 tIha) was recorded on Hira-I, Hira-2 and ACI-l also gave. the better yield 9.72 tlha and 9.70 tlha respectively. The lowest grain yield (7.90 tlha) was found in Krishan-2 which was statistically identical with Richer-10l (7.92 t/ha). It was observed that disease incidence and severity was gradually increased from flowering stage to maturity stage, with the age of the plant. Minimum incidence and severity gave the maximum yield.