Comparative Analysis of Powdery Mildew Disease Resistance and Susceptibility in <i>Brassica</i> Coenospecies

<i>Erysiphe cruciferarum</i>, a causative agent of powdery mildew disease, has emerged as a serious threat in <i>Brassica juncea</i> and its closely related species. To date, no resistant cultivars have been identified in Brassica species against powdery mildew. Here, we used histopathological, biochemical, and molecular approaches to elucidate the powdery mildew disease progression and host responses in three Brassica cenospecies, namely <i>B. juncea</i>, <i>Camelina sativa</i>, and <i>Sinapis alba</i>. Based on the results of disease progression, <i>S. alba</i> was found to be extremely resistant to powdery mildew infection, whereas <i>B. juncea</i> and <i>C. sativa</i> were highly vulnerable. In addition, the disease spread rate to uninfected parts was comparatively higher in <i>B. juncea</i> and <i>C. sativa.</i> Histopathological results revealed more pathogen-induced cell death in <i>B. juncea</i> and <i>C. sativa</i> compared to <i>S. alba</i>. We also examined the role of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in <i>B. juncea</i>, <i>C. sativa</i>, and <i>S. alba</i> after powdery mildew infection. Based on our findings, the enzyme activity of SOD, POD, and CAT was relatively higher in <i>S. alba</i> then that of <i>B. juncea</i> and <i>C. sativa</i> after powdery mildew infection. Furthermore, we evaluated the expression levels of salicylic acid (SA) signature genes, including pathogenesis-related protein viz., <i>PR1</i>, <i>PR2</i>, and <i>PR5</i> in <i>B. juncea</i>, <i>C. sativa</i>, and <i>S. alba</i> after <i>E. cruciferarum</i> infection. Based on our findings, the expression levels of SA marker genes <i>PR1</i>, <i>PR2</i>, and <i>PR5</i> increased in all three species after infection. However, the fold change was relatively higher in <i>S. alba</i> than in <i>B. juncea</i> and <i>C. sativa.</i> In future, further studies are required to identify the potential candidates in <i>S. alba</i> that are involved in powdery mildew disease resistance.