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Evaluation of Fungicides Against Purple Blotch Complex of Onion (alternaria Porri and Stemphylium Botryosum) for Seed Production

M. N. Uddin
MS Student
Department of Plant Pathology, Sher-e- Bangla Agricultural University, Dhaka-1207, Bang;adesh

M. R. Islam
Associate Professor
Department of Plant Pathology, Sher-e- Bangla Agricultural University, Dhaka-1207, Bang;adesh

N. Akhtar
Professor
Department of Plant Pathology, Sher-e- Bangla Agricultural University, Dhaka-1207, Bang;adesh

A. N. Faruq
Lecturer
Department of Plant Pathology, Sher-e- Bangla Agricultural University, Dhaka-1207, Bang;adesh

Abstract/ Executive Summary:

Five fungicides viz., Dithane M-45 (Mancozeb), Bavistin 50 WP (Carbendazim), Ridomil MZ-72 (Metalaxyl + Mancozeb), Rovral 50 WP (Iprodione) and Tilt 250 EC (Propiconazole) were evaluated against purple blotch complex of onion (Var.-Taherpuri) caused by Alternaria porri and Stemphylium botryosum in field condition for seed production. Bulb treatment with either Dithane M-45 (0.45 %) or Rovral 50 WP (0.2 %) followed by foliar spraying with the same at 10 days interval reduced disease incidence (19.95 %, 13.63 %) and severity (38.87 %, 34.59 %), and increased seed yield by 64.82 % and 42.18 % respectively. In post harvest seed health test in the laboratory, less seed infection (7.04 %, 9.21 %) by Alternaria porri and the higher seed germination (88.48 %, 85.64 %) in compare to untreated control was recorded in the seed sample harvested from Dithane M–45 and Rovral 50 WP treated plot, respectively.

Keywords: Onion, Seed, Fungicides, Purple blotch, Stemphylium botryosum

Location: Farm of Sher-e- Bangla Agricultural University (SAU), Dhaka

Start Date: 00-11-2004

End Date: 00-03-2005

Program Area: Seed Technology

Commodity: Fungicide

Objectives:

To screen out the effective fungicides for the management of the purple blotch complex of onion for seed production

Methodology:

Five fungicides were evaluated against purple blotch complex of onion in the Farm of Sher-e-Bangla Agricultural University (SAU), during winter season of 2004 - 2005. Bulb treatment with Dithane M-45 (0.45%), Bavistin (0.1%), Ridomil MZ-72 (0.2%), Rovral 50 WP (0.2%), Tilt-250 EC (0.2%) and plain water (control) followed by foliar spraying with the respective fungicides were evaluated in field condition. Spraying was started from 15 days after bulb germination and 6 spraying were done at 10 days intervals with a hand sprayer. Isolation and identification of pathogen were made by direct stereomicroscopic observation and by inoculating sample tissues on Potato Dextrose Agar (PDA) medium according to CMI description.

Data were collected on leaf infection and percent Leaf Area Diseased (LAD) and calculated in terms of disease incidence and disease severity (PDI) by following formulae-

Disease incidence = Number of infected leaf ÷ Total number of inspected leaf X 100

PDI = [(Total sum of numerical ratings) ÷ (Number of observation X Maximum disease rating in the scale)] X 100

The 0-5 disease scoring scale was used to estimate the disease severity (PDI-Percent Disease Index) of purple blotch complex of onion for each unit plot under each treatment. The scale
was followed by Islam et al. as described below:
0 = no disease symptoms in the plant
1 = a few spots towards the tip, covering less than 10% leaf area
2 = several dark purplish brown patches covering less than 20% leaf area
3 = several patches with paler outer zone, covering up to 40% leaf area
4 = long streaks covering upto 75% leaf area or breaking of leaves / stalks from the centre
5 = complete drying of the leaves/ stalks or breaking of the leaves / stalks from the base
Seed health study of harvested seeds was performed following ISTA rules. Two hundreds seeds were randomly selected from each treatment and examined for seed infection and germination. Infected seeds (Alternaria porri) were counted simultaneously with germination test under stereomicroscope. The percent seed infection was calculated for each treatment.

Source of Information: J. agric. educ. technol. 9(1&2):83-86, (2006)

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The highest seed germination was recorded in the seed sample picked up from Dithane M-45 treated plot (88.48%), which was followed by Rovral 50 WP (85.64%), Ridomil MZ-72 (85.56%), Bavistin 50 WP (83.91%) and Tilt 250 EC (83.55%). All the treatments differed significantly from the control (67.62%). The lowest seed infection was recorded in case of Dithane M-45 (7.04%). The second lowest seed infection was recorded in case of Rovral 50 WP treated plot (9.21%). The highest seed infection was noted in control (17.44%) preceded by Tilt 250 EC (15.81%), Ridomil MZ-72 (12.41%) and Bavistin 50 WP (11.06%).

Knowledge Management: Journal