Abstract
Bipolaris sorokiniana (Sacc.) is considered as one of the most devastating seed borne fungal
pathogens causes leaf blight of wheat in Bangladesh. The pathogen attacks all above and
below ground parts of wheat plant is very difficult to control due to its morpho-genetical
diversity. Most widely cultivated wheat varieties viz. Sonalika, Kanchan, BARI Gom 21,
BARI Gom 23, BARI Gom 24, BARI Gom 25, BARI Gom 26 were collected from major
wheat growing areas of Bangladesh for isolation of the seed borne B. sorokiniana. The
germination percentage of the seed samples ranged from 90-98% in all varieties except
BARI Gom 24 from Chuadanga (Ch 24) and Kanchan from Gazipur (GaK). A total of 82
isolates of B. sorokiniana were isolated from the seed samples and subjected to further
study in the laboratory. On the basis of morphology the isolates of B. sorokiniana were
divided into ten groups. The color of the isolates varied from dark black, dark black with
white mycelia edge, dull black, whitish black, white and grayish white. The nature of the
isolates was compact, loose and fluffy; the marginal edge of the isolates wasas regular and
irregular. The highest mean radial growth (8.00 cm) was recorded in white regular
compact morphological group and the lowest (4.70 cm) was in the dull black irregular
compact group. Most of the conidia were ovate to ovclavate and hyaline to dark brown.
The septations of conidia were 2-7 but varied up to 11 to 13. The mean length of conidia
was ranged from 38.60-78.30 µm, while mean breadth of conidia ranged from 10.00-29.60
µm. Dark black colored morphological group produced highest number (38×106) of
conidia and white colored morphological group produced the lowest number (1.0×106) of
conidia. Thirty representative isolates from 10 morphological groups were studied for
their pathogenicity. Among the ten morphological groups, three groups G9 (dark black
irregular loose) showed higher aggressiveness in both wheat seed varieties Sonalika and
BARI Gom 21 followed by G0 (grayish white irregular fluffy) and G6 (whitish black
regular compact). The representative isolates from 10 morphological groups were further
studied for their genetic relationship using 11 primers to analyze the genetic diversity by
Random Amplified Polymorphic DNA (RAPD). The primers produced altogether 85
bands which all were observed as polymorphic. The length of amplified DNA fragments
ranged from 100 to 1200 bp. Average gene diversity (h) and Shanon's information index
(1) consider all the primers against different isolates for all loci were 0.33 and 0.50. The
values of pair-wise comparisons of Nei's (1972) genetic distance (GD) between the fungal
isolates were computed from the combined data for all primers and values ranged from
0.112 to 1.147. The values indicated that the isolates showed variation in genetically. All
the isolates of B. sorokiniana did not show same aggressiveness. On the other hand, same
aggressiveness groups were not confirmed to the samee phenotype rather the different
aggressiveness groups regarding distributed in both the major two groups. From the
study it may be concluded that a diverse groups of B. sorokiniana are available in
Bangladesh. Morphological characters are variable and convergent in nature but
molecular characters are stable and therefore more reliable to evaluate the diversity of B. sorokiniana.