Test site: The laboratory experiment was carried out in the Seed Pathology Center, Department of Plant Pathology, Bangladesh Agricultural University (BAU), Mymensingh, Bangladesh. The field trial was carried out at the Field Laboratory, Department of Plant Pathology, BAU, Mymensingh, Bangladesh during 2000-2001 and 2001-2002 wheat growing seasons. The soil of the experimental plot was sandy loam in texture belonging to Old Brahmaputra Flood plain under Agro Ecological Zone 9.
Laboratory experiment:
Preparation of inoculum: Three virulent pahotype of Bipolaris sorokiniana (S-HS-2-3-4-5-6-7, MS-HS-2-6 and MS-S-3-5-8-9-10-12) were used in this study. The pathotypes were identified in 1999-2000 from Bangladesh. Inocula were prepared following the CIMMYT method. The conidia of Bipolaris sorokiniana were collected from 10 day old PDA culture incubated at 22-24°C under alternate cycle of NUV and normal light (12/12 h) and conidial suspension were prepared with sterilized water. The suspension was sieved through a double layer of cheese cloth to remove mycelial fragments and conidiophores. One drop of tween-20 (Polyoxyethylene 20 sorbitan monolaurate) was added to the suspension to maintain uniform dispersion of conidia in suspension. The concentration of conidial suspension was adjusted to 6x104 conidia p mL-1.
Treatment used: There were 15 treatment combination which were as follows:
| T1 |
= |
Control, |
| T2 |
= |
Bion @ 50 mg p L-1, |
| T3 |
= |
Bion @ 25 mg p L-1, |
| T4 |
= |
Tilt @ 0.1%, |
| T5 |
= |
Tilt @ 0.05%, |
| T6 |
= |
Amistar @ 0.1%, |
| T7 |
= |
Amistar @ 0.05%, |
| T8 |
= |
Tilt @ 0.1% + Bion @ 50 mg p L-1, |
| T9 |
= |
Tilt @ 0.1% + Bion @ 25 mg p L-1, |
| T10 |
= |
Tilt @ 0.05% + Bion @ 50 mg p L-1, |
| T11 |
= |
Tilt @ 0.05% + Bion @ 25 mg p L-1, |
| T12 |
= |
Amistar 0.1% + Bio n @ 50 mg p L-1, |
| T13 |
= |
Amistar @ 0.1% + Bion @ 25 mg p L-1, |
| T14 |
= |
Amistar @ 0.05% + Bion @ 50 mg p L-1 and |
| T15 |
= |
Amistar @ 0.05% + Bion @ 25 mg p L-1. |
Laboratory assay of leaf spot reaction: Under this experiment the seeds were treated as per treatment combination for 6 h by dipping method and allowed to dry up on filter paper for 12 h. The treated seeds were sown in pots, where the pot soil contains soil and compost in 4:1 ratio. Plants of three leaf stages were inoculated with a spore suspension (6x104 spore p mL-1) using a self-compressed hand sprayer. Then pots were covered with previously moistened plastic bags for 24 h in darkness. Continuous misting was provided by humidifiers during every 20 min interval. Inoculated leaves were then cut into pieces (8 cm). The cut pieces were placed on Benzimidazole agar medium (150 mg Benzimidazole in 1000 ml of 1% water agar) and incubated at 25°C for 5 days. After incubation on Benzimidazole agar, percent Leaf Area Diseased (LAD) for each leaf segment was measured.
Field experiment
Land preparation: The experimental plot was prepared by thoroughly ploughing followed by laddering to have a good tilth and finally the land was properly leveled before sowing. Weeds and stubbles were removed from the field. Fertilizers and manures were applied to the field as per recommendation of BARC . The sources of fertilizers used for N, P, K, S and Zn were urea, TSP, MP, Gypsum and Zinc oxide. The full dose of TSP, MP, Gypsum and Zinc oxide were applied at final land preparation before sowing. Urea was applied in three splits, the first split was applied during final land preparation, and the second and third splits were applied at active tillering stage and panicle initiation stage, respectively. Cow dung @ 10 ton p ha-1 was applied during final land preparation. The experiments were laid out inRCBD having three replication for each treatment. The individual plot size was 1x1 m. There were six rows in each unit plot having 15 cm distance between the rows. There were 15 treatment combinations as described above. Block to block and plot to plot distances were 1 and 1 m, respectively.
Seed sowing: Kanchan a popular variety of wheat was used in this experiment. Seeds were treated with inducer as well as with different chemical combinations for 6 h and then were allowed to dry up on filter paper for 12 h. Seeds for each plot were sown at the rate of 120 kg p ha-1 The seeds were sown in the field continuously in lines and were covered by soil with the help of hand.
Intercultural operations: The field micro plots were irrigated twice. First irrigation was performed at maximum tillering stage and second irrigation was done at panicle initiation stage. Weeding was done twice; Firstly at 25 days after sowing and secondly at 45 days after sowing.
Recording data on disease severity: Leaf blight severity was determined at three growth stages of plant namely, heading stage, flowering stage and hard dough stage. Evaluation of leaf blight severity was done by double digit scale of Saari and Prescott. The first digit (D1) indicates the disease progress in height of the plant in 0-9 scale. The second digit (D2) represents the percentage area covered by the blight pathogen on the flag leaf and one below it, which is as follows: 10% = 1, 20% = 2, 30% = 3, 40% = 4, 50% = 5, 60% = 6, 70% = 7, 80% = 8, 90% = 9. Data on yield contributing characters were determined following the method of Hossain and Azad (1992). Data was collected from 18 tagged plants of each unit of plot.
Analysis of data: The data on various parameters were analyzed using analysis of variance to find out variation obtained from different treatments. Treatment means were compared by DMRT.