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Development of Mild Strains of Papaya Ringspot Virus-papaya Strain

S.MOWLICK
Regional Agricultural Research Station, BARI, Rahmatpur, Barisal, Bangladesh

A.M. AKANDA
Department of Plant Pathology, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh

A.H.M.A. RAHMAN
School of Agriculture and Rural Development, Bangladesh Open University, Gazipur, Bangladesh

Abstract/ Executive Summary:

An attempt was made with BARI papaya-1 to develop the mild strains of Papaya ringspot virus-papaya strain (PRSV-P) to use in cross protection. Three mutagents (viz. nitrous acid, sodium azide and UV radiation) with different concentrations and exposure time were used in this experiment. Mutagenic treatments of extraction of PRSV-P infected sap with 0.075M nitrous acid, 2% sodium azide, and exposure to UV radiation for 1 and 2 minutes were observed to be the best in the production of effective mild strains of PRSV-P. The mild strains of PRSV-P containing papaya seedlings were faced to challenge inoculation test. It was observed that younger seedling condition delayed the virus infection as compared to older ones.

Keywords: PRSV-P, Mutagenic treatments, Cross protection.

Location: Bangabandhu Sheikh Mujibur Raman Agricultural University, Gazipur

Start Date: 00-03-2002

End Date: 00-12-2002

Program Area: Pest Management

Commodity: Diseases

Objectives:

To develop mild/avirulent strains of PRSV-P through mutagenic treatments and to test their effectiveness.

Methodology:

The research was conducted at the research farm as well as laboratory of Bangabandhu Sheikh Mujibur Raman Agricultural University, Gazipur during March 2002 to December 2002 as a part of thesis work. Seedlings of papaya variety ‘Shahi’ (BARI papaya1) was raised in earthen pots and maintained in an insect proof net house. Three mutagents (viz. nitrous acid, sodium azide and UV radiation) were used for developing the mild strains of PRSV-P. Nitrous acid was prepared according to the procedures followed by Yeh and Gonsalves (1984). Different concentrations of 50 ml sodium acetate (0.05M, 0.075M, 0.1M and 0.125 M) were adjusted to pH 6 by adding acetic acid. The mixtures were incubated at 20C for 30 minutes. Then the reaction was stopped by adding equal volume of 0.1 M potassium phosphate buffer (pH 7). 10% sodium azide solution was prepared from which a series of solution i.e., 5%, 4%, 3%, 2% and 1% solution were made. UV radiation available in the clean bench of microbiology lab of BSMRAU was used in the mutagenic treatment. Severely PRSV-P infected papaya leaves were collected from the experimental field and ground in distilled water (10g/10ml). Then the macerated leaf tissues were treated with freshly prepared nitrous acid using different concentrations each for 10 minutes. The samples were immediately inoculated to 100 papaya seedlings with the four selected concentrations, where 25 seedlings were inoculated with each of the concentrations. All these activities were performed in an insect proof net house and the seedlings were managed with regular care. The inoculation was achieved by using 0.1 M potassium phosphate buffer (pH -7) and carborandum powder. A total of 25 seedlings were inoculated with fresh sap using potassium phosphate buffer and corborandum powder, which were treated as control. Similarly, the macerated leaf tissues were treated with different concentrations of sodium azide (i.e. 5% to 1%) each for 10 minutes and inoculated to papaya seedlings. In case of UV-radiation treatments, the macerated leaf tissues were filtrated through cheese cloth and crude sap was placed in five petridishes. The petridishes were then exposed under UV radiation in the clean bench for 1 minute for 1st treatment, 2 minute for 2nd treatment, 3 minute for 3rd treatment, 4 minute for 4th treatment, 5 minute for 5th treatment. The samples were then immediately inoculated to papaya seedling following the previous procedures. In every case 75 days old papaya seedling were used for inoculation. The papaya seedlings inoculated along with control were regularly inspected in the net house for the appearance of symptoms up to 14 days. The mild and no symptoms possessing papaya seedlings were further inoculated with sever symptoms for evaluation of the mild strains. The asymptomatic plants were inoculated with PRSV-P infected test sample every 14 days interval for three times maintaining appropriate control. The inoculation was done on the upper leaves of the papaya seedling with severely PRSV-P infected crude leaf sap. Then the seedlings were placed in the field for observation of PRSV-P symptoms in the leaves. This process is popularly known as challenge inoculation which was described by Yeh et al. (1988).

Source of Information: J Agric Rural Dev 5(1&2), 94-97, June 2007 ISSN 1810-1860

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Mild strains of Papaya ringspot virus-Papaya strain (PRSV-P) can be developed successfully by treating the virus infected sap with mutagens like nitrous acid, sodium azide and UV radiation. Among these mutagens 0.075 M nitrous acid, 2% sodium azide and exposure to UV radiation for 1 and 2 minutes were observed to effective. The mild strains might be applied for using cross protection against severe strains of PRSV-P.

Knowledge Management: Journal