Differences in the transcriptional immune response to Albugo candida between white rust resistant and susceptible cultivars in Brassica rapa L.

Albugo candida causing white rust disease decreases the yield of Brassica rapa vegetables greatly. Resistant and susceptible cultivars in B. rapa vegetables have different immune responses against A. candida inoculation, however, the mechanism of how host plants respond to A. candida is still unknown. Using RNA-sequencing, we identified differentially expressed genes (DEGs) between A. candida inoculated [48 and 72 h after inoculation (HAI)] and non-inoculated samples in resistant and susceptible cultivars of komatsuna (B. rapa var. perviridis). Functional DEGs differed between the resistant and susceptible cultivars in A. candida inoculated samples. Salicylic acid (SA) responsive genes tended to be changed in their expression levels by A. candida inoculation in both resistant and susceptible cultivars, but different genes were identified in the two cultivars. SA-dependent systemic acquired resistance (SAR) involving genes were upregulated following A. candida inoculation in the resistant cultivar. Particular genes categorized as SAR that changed expression levels overlapped between A. candida and Fusarium oxysporum f. sp. conglutinans inoculated samples in resistant cultivar, suggesting a role for SAR in defense response to both pathogens particularly in the effector-triggered immunity downstream pathway. These findings will be useful for understanding white rust resistance mechanisms in B. rapa.

Genetics of Clubroot and Fusarium Wilt Disease Resistance in Brassica Vegetables: The Application of Marker Assisted Breeding for Disease Resistance.

The genus Brassica contains important vegetable crops, which serve as a source of oil seed, condiments, and forages. However, their production is hampered by various diseases such as clubroot and Fusarium wilt, especially in Brassica vegetables. Soil-borne diseases are difficult to manage by traditional methods. Host resistance is an important tool for minimizing disease and many types of resistance (R) genes have been identified. More than 20 major clubroot (CR) disease-related loci have been identified in Brassica vegetables and several CR-resistant genes have been isolated by map-based cloning. Fusarium wilt resistant genes in Brassica vegetables have also been isolated. These isolated R genes encode the toll-interleukin-1 receptor/nucleotide-binding site/leucine-rice-repeat (TIR-NBS-LRR) protein. DNA markers that are linked with disease resistance allele have been successfully applied to improve disease resistance through marker-assisted selection (MAS). In this review, we focused on the recent status of identifying clubroot and Fusarium wilt R genes and the feasibility of using MAS for developing disease resistance cultivars in Brassica vegetables.