VARIABILITY OF BIPOLARIS SOROKINIANA (SACC.) SHOEMAKER AND MANAGEMENT OF LEAF BLIGHT OF WHEAT

Abstract

The present research work carried out to determine the variability of B. sorokiniana, causal agent of leaf blight of wheat (BpLB) and its management. Diseased leaf samples of twenty-one wheat varieties from eight districts of Bangladesh were collected. A total of 35 fungal species belongs to 20 genera were isolated, the frequency percentage of B. sorokiniana ranged from 6.67-85.71% based on varieties. It was the maximum in Joypurhat district and minimum in Kushtia district. Association of Bipolaris cynodontis, Drechslera hawaiiensis and Pestalosiopsis guepinii with wheat were new record. Bispora antenata and Drechslera dematioadea were new recorded fungi for Bangladesh. Total 174 isolates of B. sorokiniana were obtained and 150 isolates under 8 different cultural groups were evaluated for morphological, physiological and pathogenic variability. The colour of colonies varied from ash to whitish, brownish, blackish, greenish ash and black with smooth or wavy margin, and white mat colonies with few conodia. Compatibility test reveals that 53.34% confrontations were incompatible. Ten fungicides were evaluated against B. sorokiniana isolates in vitro, Tilt 250 EC and Folicur 250 EC were identified as the complete inhibiting chemical fungicides. Out of 10 leaf extracts, Azadirachta indica and Citrus limon showed best inhibition on B. sorokiniana isolates. The present investigation suggests that Trichoderma harzianum and T. viride showed promising inhibitory effect on B. sorokiniana isolates. From field experiments, effective fungicides (Tilt 250 EC/Folicur 250 EC) two spray at 65 days and 80 days after sowing, at standard dose (0.1%) will be more fruitful on reducing disease severity and increasing yield than the standard three spray schedule. Estimation of yield loss of wheat due to Bipolaris leaf blight (BpLB), the average yield loss was 28.68-29.19%, with 1000 grain weight more than 15% lower than protected plot. From the screening of wheat germplasms against Bipolaris leaf blight (BpLB), 1.63, 39.02, 54.47, 4.88 percent genotypes were selected as resistant (R), moderately resistant (MR), moderately susceptible (MS) and susceptible (S), respectively. There was no genotype as highly susceptible (HS). Seed health test reveals that all seed samples were infected by B. sorokiniana in various degrees and black point seeds show lower seed viability, germination and emergence percentage, vigour index etc. than apparently healthy seeds.