Pathotype variation of Albugo candida, the cause of white rust disease in rapeseed-mustard
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Date
2019-09
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
White rust disease of rapeseed-mustard is one of the most important disease which severely affects production and productivity of the crop. The obligate and high variable nature of the pathogen poses a challenge for the eco-friendly management of the disease. A limited work has been done in India/world on the variability of this pathogen. So, present investigation has been done on the pathotype variability of A. candida based on molecular, morphological and pathogenic characterization of 33 A. candida isolates belongs to 12 different states of India and from 09 Brassica spp. Molecular characterization using 12 SSR markers, among them 05 viz. DM 3, DM 16, DM 22, M31 and Pv65 showed high polymorphism. Molecular characterization using ITS and COX2 gene yielded 1250bp and 650bp band respectively and maximum parsimony tree showed 15 and 13 cluster from 33 A. candida isolates respectively. Morphological characterization based on the shape of sporangia, 33 A. candida isolates were categorized in 03 groups viz. globose, ovoid and irregular while based on size, isolates were grouped in Microsporangia (14-17μm), Mesosporangia (17.10-20μm) and Macrosporangia (>20μm) with largest size (22μm) of sporangia in Ac-Smr (Sirmaur, HP) and smallest (14.63μm) in Ac-Knp (Kanpur, UP). Based on pustule pattern on B. juncea cv. Varuna, isolates were categorized in 05 groups viz. Separate circular; Coalesced circular, Scattered and pin head; Restricted near veins and veinlets and Restricted near veins and veinlets separate or coalesced circular type pustules. On the basis of virulence on 19 Brassica genotypes, 33 A. candida isolates were categorized into 04 different groups viz. highly virulent, virulent, moderately virulent and least virulent. On the basis of aggressiveness, isolates were categorized into 04 different groups viz. highly aggressive, aggressive, moderately aggressive and least aggressive. Based on the cross infectivity on different Brassica spp., isolates were grouped in 19 different pathotypes. Based on the B. juncea cultivar (out of 7) and on different Brassica spp. 03 major groups has been identified viz. Group Ia was pathotype of B. juncea, Group Ib was pathotype of B. juncea cv. Cutlass, Group Ic was pathotype of B. juncea cv. Donskaja, Group Id was different B. juncea pathotype that showed disease reaction on B. oleracea, Group Ie was B. juncea pathotype that showed disease reaction on B. carinata cv. Kiran. Group II was pathotype of B. rapa var. Toria, Group III was pathotype of B. rapa. Finally, from 33 A. candida isolates a total of 21 pathotypes has identified on the basis of combined grouping on pathogenicity reactions on host differential and ITS and COX2 gene sequence analysis and new nomenclature has been given as per International standard, out of which 15 pathotypes showed more virulence to B. juncea that named as AC2-1 to AC-15, 06 pathotypes showed virulence to B. rapa that named as AC7-1 to AC7-6. The different A. candida pathotypes identified from different geographical regions of India could be utilized for the identification and deployment of resistant cultivar in major mustard growing areas.
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