Identification and nomenclature of Albugo candida pathotypes of Indian origin causing white rust disease of rapeseed-mustard

Abstract

The highly variable nature of Albugo candida pathogen in terms of number of races/pathotypes poses a challenge in the proper identification. Therefore, in this study characterization and identification of 33 A. candida isolates of Indian origin have been done on the basis of molecular and host differentials studies. Molecular characterization using ITS and COX2 gene yielded 1250 bp and 650 bp bands while maximum parsimony trees showed 15 and 13 clusters from 33 A. candida isolates, respectively. On the basis of pathogenicity reactions on 19 host differentials of different Brassica spp., 3 major groups have been identified as Group Ia, Ib, Ic, Id, Ie, II, and III. Group Ia was the pathotype of Brassica juncea, Ib- B. juncea cv. Cutlass, Ic- B. juncea cv. Donskaja, Id- a different B. juncea pathotype that showed disease reaction on B. oleracea, Ie- a different B. juncea pathotype that showed disease reaction on B. carinata cv. Kiran, Gropu II- B. rapa var. Toria, Group III- B. rapa pathotypes, respectively. Finally, from 33 A. candida isolates a total of 21 pathotypes have been identified on the basis of combined grouping of pathogenicity reactions on host differentials and ITS and COX2 gene sequence analysis and new nomenclature has been given as per the International standard, out of which 15 pathotypes showed more virulence to B. juncea that named as AC2–1 to AC2–15, 6 pathotypes showed virulence to B. rapa that named as AC7–1 to AC7–6. A. candida pathotypes identified from different geographical regions of India could be utilized for the identification and deployment of the resistant cultivar in major mustard growing areas.