Genetic manipulation of Indian mustard genotypes with WRR-gene(s) confers resistance against Albugo candida.

BACKGROUND: Brassica species is the second most important edible oilseed crop in India. Albugo candida (Pers.) Kuntze, a major oomycete disease of oilseed brassica causing white rust, leads to 60% yield loss globally. The prevalence of A. candida race 2 (Ac2V) that specifically infects B. juncea, coupled with limitations of conventional methods has resulted in a dearth of white rust resistance resources in cultivated varieties. METHODS AND RESULTS: In an effort to develop resistant plants, Agrobacterium mediated genetic transformation of three B. juncea genotypes viz., susceptible host var. Varuna, along with its doubled haploid mutant lines C66 and C69 (showing moderate tolerance to field isolates of A. candida) was initiated to transfer resistance genes (WRR8Sf-2 and WRR9Hi-0) identified in Arabidopsis thaliana against race Ac2V, that encode for Toll-like/interleukin-1 receptor-nucleotide binding-leucine-rich repeat proteins that recognize effectors of the pathogen races. CONCLUSIONS: Our results demonstrate that introduction of resistance genes from a tertiary gene pool by genetic transformation enhances disease resistance in B. juncea genotypes to a highly virulent Ac2V isolate.

Resistance strategies for defense against Albugo candida causing white rust disease.

Albugo candida, the causal organism of white rust, is an oomycete obligate pathogen infecting crops of Brassicaceae family occurred on aerial part, including vegetable and oilseed crops at all growth stages. The disease expression is characterized by local infection appearing on the abaxial region developing white or creamy yellow blister (sori) on leaves and systemic infections cause hypertrophy and hyperplasia leading to stag-head of reproductive organ. To overcome this problem, several disease management strategies like fungicide treatments were used in the field and disease-resistant varieties have also been developed using conventional and molecular breeding. Due to high variability among A. candida isolates, there is no single approach available to understand the diverse spectrum of disease symptoms. In absence of resistance sources against pathogen, repetitive cultivation of genetically-similar varieties locally tends to attract oomycete pathogen causing heavy yield losses. In the present review, a deep insight into the underlying role of the non-host resistance (NHR) defence mechanism available in plants, and the strategies to exploit available gene pools from plant species that are non-host to A. candida could serve as novel sources of resistance. This work summaries the current knowledge pertaining to the resistance sources available in non-host germ plasm, the understanding of defence mechanisms and the advance strategies covers molecular, biochemical and nature-based solutions in protecting Brassica crops from white rust disease.

Biochemical aspects of pathogenic variability in white rust infected Indian mustard.

White rust caused by Albugo candida, an oomycete pathogen, is a devastating disease of Brassica juncea (Indian mustard) worldwide. There is a need to screen virulent white rust isolates to challenge the developed white rust-resistant B. juncea cultivars to screen their resistance potential. The current study explores pathogenic and biochemical response of Indian mustard to white rust isolates collected from three different geographic locations of India. The observations refine our understanding of the disease severity in India. Disease progression and biochemical responses were studied in the cotyledonary as well as true leaf stage of the B. juncea cultivar Varuna at different time points. The biochemical findings highlight the fluctuation of significant biochemical parameters such as total proteins, sugars, and phenols, superoxide dismutase, and hydrogen peroxide during the A. candida infection in B. juncea.