Abstract
Wheat (Triticum aestivum L.), an important cereal crop is produced all over the country. Leaf blight caused by Bipolaris sorokiniana is a common constraint of limiting wheat production in Bangladesh. Variation of Bipolaris sorokiniana in respect of physiologic specialization and pathotypes and their effect on grain formation of wheat were studied. Bipolaris sorokiniana was isolated from 216 different samples of leaves and seeds from 16 different major wheat growing areas of Bangladesh. The isolates were studied for their physiological group (race) based on colony colour (black, white, blackish and whitish), colony shape (regular and irregular) and compactness (compact or loose). These isolates were grouped into 13 groups as 1 = Black compact regular, 2 = Black compact irregular, 3 = Black regular loose, 4 = Black irregular loose, 5-White compact regular, 6 White regular loose, 7 White irregular loose, 8= Blackish white compact regular, 9 = Blackish white compact irregular, 10 = Whitish black compact regular, 11 = Whitish black compact irregular, 12 = Blackish white regular loose and 13 = Whitish black regular loose comprising of 51.53%, 17.18%, 5.34%, 0.38%, 8.78%, 3.43%, 0.38%, 3.05%, 0.38%, 5.34%, 0.38%, 1.53% and 2.30% of collected isolates, respectively. Forty six representative isolates from 13 different physiologic groups or races were tested against 5 China and 6 Brazil differential variety for determination of pathotypes. Six pathotypes were recorded. Among the six pathotypes, Pathotype no. 3 comprised of 74% of all isolates tested, where Pathotype no. 1 and 2 each comprised of 4.34%, Pathotypes no. 4, 5 and 6 comprised of 2.17%, 8.69% and 6.52% isolates, respectively. Both pot and field experiments were conducted to find out the effect of different pathotypes of Bipolaris sorokiniana on grain formation and yield of wheat by inoculating at maximum tillering stage, flag leaf stage and flowering stage. The pot and field experiments by artificial inoculation revealed that all the pathotypes of B. sorokiniana showed alike effect on grain yield of wheat. The yield of wheat decreased up to 68.97%, 125.11% and 81.20% in pot experiments, respectively over, the control (Tilt sprayed plots) when inoculated at maximum tillering stage, flag leaf stage and flowering stages. But in case of field experiments, the grain yield decreased up to 43.75%, 40.0% and 51.17%, respectively over the control (Tilt sprayed plots) when the wheat plants were inoculated by Bipolaris sorokiniana at maximum tillering stage, flag leaf stage and flowering stages. The inoculation studies also showed that pathotypes did not result any significant variation in respect of the formation of healthy grains (grade 0), but they differed significantly from the control treatment.