MORPHOLOGICAL, CULTURAL AND MOLECULAR VARIATION AND VIRULENCE OF BIPOLARIS SOROKINIANA IN WHEAT

Abstract

Monoconidial one hundred and twenty isolates of Bipolaris sorokiniana of wheat were isolated and identified based on morphological and ITS1 and ITS4 based molecular parameters. These isolates were isolated from seeds and leaf of 7 varieties of wheat collected from 7 major wheat growing regions of Bangladesh. The collected isolates differed significantly in respect of radial mycelial growth rate, color of colony, surface texture of colony, shape of colony, number of conidia production, shape and color of conidia etc. The mycelial growth rate was recorded from the range of 1.39 (MMPS 66) to 4.46 mm/day (JSBS 88). Maximum (73) isolates had blackish white colored colonies. Forty-two isolates had blackish colored colonies and five isolates had whitish colored colonies. Among 120 isolates, 65 isolates produced regular shaped colonies and 55 isolates had irregular shaped colonies. One hundred twenty isolates showed smoothy and wooly surface texture of colony and 18 isolates showed effuse and rough surface texture of colony. Among 120 isolates, maximum number of conidia/cm² was counted in isolates no BAKS 11 which was 416.17×10

and minimum number of conidia/cm² was 89.6×10 ii 4 found in isolates no JSBS 88. Among these isolates, 92 isolates produced brown colored conidia and 17 isolates produced deep brown colored conidia and 11 isolates produced light brown colored conidia. Among 120 isolates, the septation of conidia ranged from 1.4 to 8.6. The isolates were grouped into five groups based on their conidial shape where 57 isolates produced elliptical and straight conidia with 47.50% frequency, 13 isolates produced elliptical and curved shaped conidia with 10.83% frequency, 28 isolates produced oval shaped conidia with 23.33% frequency, 5 isolates produced round shaped conidia with 4.17% frequency and 17 isolates produced pyriform shaped conidia with 14.16% frequency. Again the isolates were grouped into twelve cultural groups based on colony morphology and surface texture of the colony. Among these cultural groups, smoothy and wooly blackish white irregular groups contain the highest number of isolates and that was 39 isolates with 32.5% frequency of the total isolates studied. The different cultural groups of Bipolaris sorokiniana showed different characteristics based on mycelial growth rate, conidia production and septation number. The radial mycelial growth rate differed from 2.67 mm/day to 4.50 mm/day. The highest growth rate counted from the group number G-12 and the lowest growth rate counted from the group number G-7. Maximum number of conidia/cm² was recorded from the group number G-7 and that was 248.93×10 4 and the minimum number of conidia/cm² was recorded from group G-12. The highest septation (7.1) was found in group G-11 and the lowest (2.44) was found in group G-1. Among these 12 groups, effuse and rough blackish irregular group (G-8) was most virulent (38.5% LAD) and effuse and rough blackish white irregular group (G-4) was low virulent group among 12 groups (2% LAD).