EFFECT OF DIFFERENT LEVELS OF SEED INFECTION BY Bipolaris sorokiniana ON SEEDLING VIGOR, LEAF BLIGHT DEVELOPMENT AND QUALITY SEED PRODUCTION OF WHEAT

Abstract

An investigation of the effect of different levels of seed infection by Bipolaris sorokiniana on seedling vigor, leaf blight development and quality seed production of wheat was carried out in the Seed Health Laboratory, Department of Plant Pathology during the period ofJuly,2007 to September, 2007 and in the farm ofShere-Bangla Agricultural University, Dhaka, Bangladesh during the period from November, 2007 to April, 2008 with six treatments viz. Tl (0% seed infection), T2 (5.1-15% seed infection), T3 (15.1-25% seed infection), T4 (25.1-35% seed infection), T, (35.1-45% seed infection) and T6 (45.l-60% seed infection). Under in vitro condition, seed germination and seedling vigor were lessened, whereas seedling infection was increased with the gradual increase of seed infection. Germination of seeds and vigor of seedlings were the highest in T) and the lowest in T6, respectiveJy. The maximum and the minimum seedling infection were recorded in T6 and T., respectively. In the field condition, significant variations were found considering number of seedlings/rrr' and number of infected seedlings/mi. The highest (122.19) and the lowest number of seedlings/m/ (90.20) were recorded in TJ and T6, respectively, whereas the maximum (25.73) and the minimum (8.54) number of infected seedlings/rrr' was found in T6 and T., respectively. Leaf blight severity (0-5 scale) on flag leaf and penultimate leaf was recorded in flag leaf stage, panicle initiation stage, flowering stage, milking stage and hard dough stage and positive corelationship was found between seed infection levels and the average disease severity. Average disease severity on leaf was found the highest in T6 and the lowest in Ti, respectively in all growth stages. The highest pJant height (89.67 em) and spike length (15.95 em) were observed in T1• The maximum number of spikelets/ear (31.24) and number of healthy spikelets/ear (30.87) were also found in T), while the maximum number diseased spikelets/ear (5.34) was found in T6. Number of grains/ear and number of healthy grains/ear were the highest in plots of TJ while number of diseased grains/ear was the highest in T6• Weight of grains/ear and weight~· , of healthy grains/ear were significantly increased with the decrease of seed infection .. In respect of grains/ear of different severity grades (0-5), the maximum Grade-O seeds were found in TJ and the maximum Grade-S seeds were recorded in T6• The highest grain yield (3.67 tJha) and straw yield (6.41 t/ha) were recorded in Th where grain yield was increase up to 38.69% over T6. Highly positive linear relationship was found between seed infection levels and incidence of Bipolaris sorokiniana on harvested seeds. Considering all this, the minimum level of seed infection by Bipolaris sorokiniana i.e. T1 (0% seed infection) showed promising results in producing high quality (Grade-O) seeds of wheat.