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Disease Assessment Key for White Rust Disease Caused by Albugo candida, in Rapeseed-Mustard



Khajan Singh Bisht, Meenakshi Rana, Pooja Upadhyay and R.P. Awasthi
 
ABSTRACT

Background and Objective: White rust disease caused by pathogen Albugo candida (A. candida) (Pers. Ex. Lev.) Kuntze. (A. Cruciferarum S.F. Gray) is one of the major diseases, responsible in reducing the yield of Rapeseed-Mustard (Brassica sp.). The main objective of this study was planned to develop photographic disease assessment keys for White rust of Rapeseed-Mustard. However, till now only diagrammatic or numerical assessment keys have been reported for screening of Rapeseed-Mustard germplasm against White rust disease but none is available on the basis of their actual photographs. Materials and Methods: Disease severity was taken on transparent graph paper. Pictures of disease free cotyledons and leaf, less than 5, 5-10, 11-25, 26-50% and more than 50% area covered by white rust pustules were observed for assessment key. Results: Rapeseed-Mustard plants were screened from seedling to maturity stage against White rust disease. The rating scale was developed from original field photographs with all above ground parts of infected plant viz. cotyledons, pods and leaves. Conclusion: In present study, the key was prepared for assessment of disease severity at cotyledonary leaf stage, pod stage and true leaf stage of plant. This would be helpful for consistent assessment of white rust disease as well as other leaf spot disease of Brassica sp.

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Khajan Singh Bisht, Meenakshi Rana, Pooja Upadhyay and R.P. Awasthi, 2018. Disease Assessment Key for White Rust Disease Caused by Albugo candida, in Rapeseed-Mustard. Plant Pathology Journal, 17: 11-18.

DOI: 10.3923/ppj.2018.11.18

URL: https://scialert.net/abstract/?doi=ppj.2018.11.18
 
Received: March 13, 2018; Accepted: May 07, 2018; Published: June 11, 2018


Copyright: © 2018. This is an open access article distributed under the terms of the creative commons attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.

INTRODUCTION

Albugo candida (Pers. Ex. Lev.), causal agent of the white rust of Rapeseed-Mustard, is an economically important and wide spread disease of cruciferous crops causing heavy yield losses all over the world. Depending on the severity of disease, the percent yield losses ranging from 1-60% in Polish or Turnip rape (Brassica rapa L.) in Canada1-4, 23-89.8% in Indian mustard [B. juncea (L.) Czern and Coss] in India5-10 and 5-10% in Australia11,12, substantial yield losses in radish (Raphanus sativus L.) has also been reported13,14. Pathogen (Albugo candida) produces white or creamy pustules on both cotyledons, true leaves and pods which reduces the photosynthetic capacity of plants and affects yield and normal plant development. Disease on the foliage affects and downgrades the leaves for sale and its human consumption as a vegetable. Disease levels on leaves, through inoculum density, affect the disease severity on cotyledon, leaves and siliqua. A lesion on foliage causes extensive distortion, hypertrophy, hyperplasia and sterility of inflorescences generally called "systemic infection". The systemic infection phase increases fruit shattering and reduces yield of mustard. Disease assessment keys, based on the host area affected, have been prepared for many diseases15-17. However, so far as the authors are aware, none is available for assessing White rust of Rapeseed-Mustard. Charts for rating the different growth stages of Rapeseed-Mustard are available18,19.

Based on the above said considerations, the main aim of study was to develop disease assessment keys for both cotyledon and leaf stages of mustard plant.

MATERIALS AND METHODS

Cotyledonary and true leaves with white rust pustules were collected from the field of Norman E. Borlaug Crop Research Centre, G.B. Pant University of Agriculture and Technology, Pantnagar and the symptoms studied during Rabi crop season 2014-15. Cotyledonary and true leaves with pustules were selected for photographs of rating scale. Pustules covering areas were included in calculation of the diseased area. Percent area covered with white rust lesions was calculated using a transparent graph paper. Photographs of disease free cotyledons and leaf, less than 5, 5-10, 11-25, 26-50% and more than 50% areas covered by white rust lesions were taken for assessment key i.e., rating scale in Table 1.

Ten plants/plot were randomly selected for the observations. Based on infected area, leaves of each plant were rated as per rating scale (0-9) and the disease severity was calculated by using the following formulae:

RESULTS AND DISCUSSION

White rust symptoms for Rapeseed-Mustard at cotyledons, true leaves and pods were given in Fig. 1, 2 and 3, respectively. To screen Rapeseed-Mustard plants right from seedling stage to maturity against White rust disease caused by pathogen Albugo candida (Pers. Ex. Lev.), the actual photograph based on 0-9 rating scale was conceptualized. The rating scale was developed from original field photographs with all above ground parts of infected plant viz. cotyledons (Fig. 1), pods (Plate 2) and leaves (Plate 3 and 4). Disease assessment key was illustrated with the following percent of severity : 0 (No pustules), 1 (Less than 5% leaf area covered by pustules), 3 (5-10% leaf area covered by pustules), 5 (11-25% leaf area covered by pustules), 7 (26-50% leaf area covered by pustules) and 9 (26-50% leaf area covered by pustules) (Plate 1). White rust disease severity scored for ten leaves from one of the plants was 3, 3, 5, 3, 3, 3, 5, 5, 3 and 3 (mean = 3.60), whereas those for ten leaves from the other plant was 5, 3, 3, 5, 3, 5, 5, 3, 3 and 3 (mean = 3.80).

Table 1:
Rating (0-9) scale for measuring disease severity of white rust

Fig. 1(a-b):
Cotyledons of mustard infected by white rust disease caused by A. candida, (a) Pustules of A. candida as scattered form on cotyledons of mustard and (b) Pustules of A. candida as circular form on cotyledons of mustard

Fig. 2(a-b):
Leaves of mustard infected by pustules of white rust disease caused by A. candida, (a) Pustules of A. candida in scattered form on leaf of mustard and (b) Pustules of A. candida in ring form on leaf of mustard

Fig. 3:
Pods of mustard infected by pustules of white rust disease caused by A. candida

Plate 1:
Rating Scale (0-9) of white rust pustules on cotyledon of Brassica juncea

Mean scores were converted to percent disease severity by using formulae given in material and methods. This resulted in 40 and 42.22% disease severity, respectively.

The overall shape of cotyledonary leaves and siliqua are similar in Mustard crop, therefore keys would permit White rust lesion assessment in all Mustard crops. Diagrammatic disease assessment key for Alternaria leaf spot was developed on the basis of proportions of surface area infected by the pathogen17. Falloon et al.20 developed (0-10) disease severity keys for downy and powdery mildew of pea and powdery scab of potato tubers. The keys were prepared from hand drawings of pea leaves and potato tubers. Godoy et al.21 illustrated diagrammatic disease severity key for Soybean rust. The assessment key showed six severity levels (0.6-78.5%). The representation of t he symptoms included tissues that became necrotic because of pustules, chlorotic halos and coalesced lesions. Disease severity key on sweet-pepper fruits for anthracnose disease was developed by Pedroso et al.22.

Plate 2:
Rating scale (0-9) of white rust on pods of Brassica juncea


Plate 3:
Rating scale (0-9) of white rust on leaf of Brassica juncea

Plate 4:
Rating scale (0-9) of white rust on leaf of Brassica juncea in different pattern

One hundred diseased fruits were collected and photographed to measure the percentage diseased area of one half of the fruit surface. Diseased Fruits were categorized into nine classes, from class 0 (0% diseased area) to class 8 (81% or more diseased area). Belan et al.23 illustrated disease assessment key for bacterial blight of coffee. The diagrammatic scale ranged from 0 (0%), 1 (0.1-0.99%), 2 (1-2%), 3 (2.01-4%), 4 (4.01-8%), 5 (8.01-16%), 6 (16.01-25%), 7 (25.01-45%) and 8 (>45.1%). The scale was appropriate to estimate disease severity of bacterial blight in coffee leaves.

CONCLUSION

Disease severity scoring keys may prove useful tools for assessing White rust and some other diseases of Rapeseed-Mustard as well, such as Alternaria blight caused by Alternaria brassicae and white leaf spot caused by Pseudocercosporella capsellae. Thus, this (0-9) rating scale can be used efficiently for screening of white rust as well as all other leaf spot diseases of Rapeseed-Mustard plants.

SIGNIFICANCE STATEMENTS

In present study, disease assessment key for White rust of Rapeseed-Mustard was developed on the basis of real photographs collected from the field. Till now only diagrammatic or numerical assessment keys have been reported for screening of Rapeseed-Mustard germplasm against White rust disease but none was available on the basis of their actual photographs.

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