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Toxin Production and Necrosis to Wheat by Bipolaris Sorokiniana

M. S. Monjil
Dept. of Plant Pathology, Bangladesh Agricultural University, Mymensingh, Bangladesh.

I. Hossain
Dept. of Plant Pathology, Bangladesh Agricultural University, Mymensingh, Bangladesh.

Abstract/ Executive Summary:

Thirteen isolates of Bipolaris sorokiniana were tested for growth study and among these Four isolates were used for necrosis toxin production. The mean radial mycelial growth of the isolates of B. sorokiniana varied significantly From one isolate to another that ranged from 15.0 to 31.0 mm and their sporulation potency (conidia/cm²) on PDA also differed significantly that ranged From 12.25x 10³ to 98.99x I0³ Culture filtrate of Four isolates of B. sorokiniana induced necrosis of wheat as visible at Four days after inoculation in wheat leaves at 3-leaf stage Following excised leaf method. No chlorosis developed in leaves of wheat inoculated with Fries medium (control). The highest leaf area diseased was caused by the toxin produced by the isolate 179a. The toxin produced by the different isolates (179a, 67b, 100a, 189a) are of different potency of causing leaf spot of wheat.

Keywords: Toxin. Bipolaris sorokiniana. Wheat, Necrosis

Location: Disease Resistance Laboratory, Department of Plant Pathology, Bangladesh Agricultural University, Mymensingh

Start Date: 00-07-2002

End Date: 00-03-2003

Program Area: Pest Management

Commodity: Diseases

Objectives:

To evaluate the comparative growth of 13 isolates of B. sorokiniana, extraction of toxin and the toxicity of culture filtrates on the development of necrosis symtoms on wheat leaves.

Methodology:

The experiment was conducted in the Disease Resistance Laboratory, Department of Plant Pathology, Bangladesh Agricultural University, Mymensingh during the period from July, 2002 to March, 2003. Thirteen isolates of Bipolaris sorokiniana which, were previously collected and preerved in the laboratory. Growth study of Bipolaris sorokiniana was carried out by using PDA plates at 25ºC for 10 days. Then the radial mycelial growth were determined. The sporulation potency of the isolates of Bipolaris sorkiniana were determined from the cultures incubated for 15 days at 24°± I ºC. The conidia produced per unit surface area was determined. The selected 13 isolates of B. sorokiniana were transferred from stock culture and were grown on PDA for 10 days at 22-24°C. Then the petridishes having B. sorokiniana were kept for 5 days under NUV light for maximum conidia formation. formation. Conidial suspension was prepared with sterilized water by collecting the conidia from the surface of PDA and filtered through cheese cloth to remove mycelial fragments and lumps of agar. The conidial suspension of each isolate was prepared to 60,000 sporeslml following the CIMMYT method. The medium consists of Ammonium tartrate, 5.0g; NH₄ NO₃, 1.0g; KH₂P0₄, 1.0g; MgS0₄.7H₂O , 0.5g; Nacl, 0.1 g; Cacl₂.2H₂O, 0.13g; Sucrose, 30g; MnS0₄.4H₂O, 1.0mg; Boric acid, 1.0 mg; CuS0₄. 0.1 mg; Znso₄ 7H₂O, 0.1 mg; Feso₄ X H₂0, 20 mg; and distilled water 1000 ml. For toxin production 4 selected isolates of B. sorokiniana viz. 100a, I 79a, 189a and 67b were transferred from stock cultures and were grown on PDA for 10 days at 22-25°C. Then the petri dishes having B. sorokiniana were kept under NUV light (12/12) for 5 days. Thereafter, spore suspension was prepared following the CIMMYT method. One millilitre aliquots of a conidial suspension with 10,000 spores/ml were transferred to 250 ml Erlenmeyer flasks containing 50 ml of modified' Fries medium supplemented with 0.1 % yeast extract. Flasks were incubated at 25°C in the dark without agitation for three weeks. Toxin containing cultures were filtered through Whatman No. I paper and then through a 0.45 µm millipore membrane adjusted to p^H 6.5 with NaOH and stored at 4°C. The inoculation of leaves of Wheat cv. Kanchan was done by using toxic culture filtrates following the excised leaf inoculation technique. Green healthy leaves were collected at three leaf stage. Injuries were made with the help of sterilized needle at the centre of the excised leaf (4.5 cm). Leaf segments were placed onto a 2 mm thick layer of Benzimidazole water agar (150 mg Benzimidazole/1000 ml of 1% water agar) in a petridish closed tightly with a lid. One droplet of culture filtrate was given on to the middle of the excised leaf, where injury was made earlier with sterilized needle. Necrotic symptoms were evaluated after 4-days of inoculation by observing the spot developed on inoculated site which was compared with uninoculated control where only fries medium placed.

Source of Information: Progress. Agrie. 14(1 & 2) : 35-38,2003,ISSN 1017-8139

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Findings of the present study proved that toxin produced by Bipolaris sorokinianu is capable of producing necrosis symptom on wheat plants.

Knowledge Management: Journal