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Identification and functional validation of white rust resistance gene in Brassica juncea

Heena Arora: University of Delhi

<div>White rust caused by <em>Albugo candida</em> is a destructive disease in many agronomically important Brassica species including <em>Brassica juncea</em>, the major oilseed crop of the Indian subcontinent. Almost all the released varieties of <em>B. juncea</em> in India are highly susceptible to the disease. Infection of leaf and inflorescence leads to massive yield losses of up to 60% or more in India. In a previous study, the locus conferring complete resistance to <em>A. candida</em> race 2V in east European gene pool line, Donskaja-IV, was mapped to linkage group A05 of <em>B. juncea</em>. The bacterial artificial chromosome (BAC) library of Donskaja-IV was screened with the tightly linked marker and the identified BAC clone was sequenced and annotated using Brassica BAC annotation pipeline tool. The annotation revealed that the A05 locus of Donskaja-IV contains a putative resistance (R) gene of coiled coil-nucleotide binding site-leucine rich repeat (CC-NB-LRR) class. Transgenic plants of Varuna, a susceptible but widely cultivated Indian variety, were raised expressing the candidate gene (<em>BjuD</em>) with its native promoter by <em>Agrobacterium</em> mediated gene transfer. Infection assays were performed on T<sub>0</sub> plants with <em>A. candida </em>isolates collected from different geographical areas of India – Bharatpur, Pantnagar, Meerut, Hisar, Bihar, Morena and Alwar. Transgenic plants showed resistance to all the isolates validating the role of gene <em>BjuD</em> in conferring broad spectrum resistance to different <em>A. candida</em> isolates. The results obtained in this study will promote development of white rust resistant lines in mustard and reduce the yield losses attributed to <em>A. candida</em>.</div>