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Evaluation of Resistance to Dark Leaf Spot (alternaria Brassicicola) in Brassica Rapa

M. A.U. Doullah
Associate Professor
Department of Plant Pathology and Seed Science, Sylhet Agricultural University, Sylhet-3100, Bangladesh

K. Okazaki
Professor
Department of Agrobiology, Niigata University, Niigata, Japan

Abstract/ Executive Summary:

Dark leaf spot (Alternaria brassicicola) is an important disease of brassica crops especially in Brassica rapa. A total of 281 cultivars of B. rapa including B. napus and B. juncea were screened in two different years by detached leaf and seedling symptom test methods. Two cultivars Edononatsu and Saori exhibited high levels of tolerance in both the years following the two inoculation methods, whereas some cultivars displayed borderline resistance and most of them were susceptible to the disease. A significant correlation (r = 0.52) found in disease severity between two years by detached leaf inoculation test. Cultivars identified as tolerant would be useful in breeding program to develop strains against dark leaf spot disease.

Keywords: Screening, Disease resistance, Dark leaf spot, Alternaria brassicicola, Brassica rapa

Location: National Institute of Agrobiological Resources, Japan and Bangladesh Agricultural Research Institute, Bangladesh

Start Date:

End Date:

Program Area: Pest Management

Commodity: Diseases

Objectives:

To evaluate the resistance to dark leaf spot of (Alternaria brassicicola) IN Brassica rapa.

Methodology:

Plant material: Genotypes of Brassica rapa used in this study were collected from Japanese seed companies, Gene Bank of the National Institute of Agrobiological Resources, Japan and Bangladesh Agricultural Research Institute, Bangladesh. Plants were grown from seeds in soil where 10-cell plastic trays (cell size: 5 cm X 5 cm) were used in a greenhouse (25^oC /15^oC day/night cycle) and liquid nutrient (N: P₂O₅: K₂O, 0.5:1.0:0.5 g/l; Hyponex, Osaka, Japan) was periodically supplied for plant growth. Fungal isolates: Alternaria brassicicola isolate Akakura obtained was used. Conidia of a 10-day old grown on PDA medium was used for artificial inoculation. The concentration of the conidial suspension at 5 X 10⁴ conidia/ml was adjusted for inoculation. Inoculation methods: Detached leaf inoculation test and seedling symptom test method was used where detached leaves and plants were scored using disease severity index ranged from 1 to 10 score were follows; 1= No spots and no yellow color on the leaf, 2= A few pinpoint spots but no yellow, 3= Some spots but no large lesions and no yellow, 4= Some spots with a few lesions surrounded by light yellow, 5-9 Increasing number and size of lesions and yellowing on the leaf, 10= Lesions with yellowing on more than 90% of the leaf. Evaluation for resistance: A total of 281 cultivars were screened by detached leaf inoculation test in year 2004. In year 2005, 131 cultivars from the total were re-screened by detached leaf and seedling symptom test methods. Correlation for disease development between two years was also determined using detached leaf inoculation methods. Statistical analysis: The experiment was arranged in a completely randomized design with three replicates (three leaves/plants per replicate) maintaining appropriate controls. Data from the experiments were subjected to analysis of variance (ANOVA) using statistics computer software (ESUMI Co. Ltd., Japan). Coefficient of correlation analysis was used to evaluate relationships using Microsoft Excel.

Source of Information: Int. J. Expt. Agric. 5(2):5-14 (2015)

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

A detail screening test was done against dark leaf spot disease caused by Alternaria brassicicola in Brassica rapa crops. Two cultivars Edononatsu and Saori showed high level of tolerance in both the years following two different inoculation methods while some other cultivars displayed different levels of disease severity against the disease.

Knowledge Management: Journal