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Histological Characterization of Host-Pathogen Interactions in Two Brassica rapa Accessions Exhibiting Resistance to Albugo candida
Ajay Kumar1, Diwaker Nandan2, Bangkim Rajkumar1 and Priya Panjabi1*
1Department of Botany, University of Delhi, Delhi-110007
2Centre for Genetic Manipulation of Crop Plants, University of Delhi South Campus, New Delhi-110021, India
ABSTRACT
Oilseed mustard, Brassica juncea, is highly susceptible to white rust disease caused by Albugo candida. The disease causes extensive yield loss in the crop and therefore it is crucial to identify and introgress loci conferring resistance to the disease in the commercial varieties. Most accessions belonging to the Indian gene-pool are highly susceptible to the disease; however, resistance sources have been previously identified in the east European B. juncea germplasm and also in the diploid progenitor species, B. rapa. We had recently identified two novel sources of resistance to A. candida in the B. rapa germplasm, YSPB-24 and Candle. In the present study, both accessions were characterized for their host-pathogen interactions. The two accessions are highly resistant to the pathogen and no pustules were observed on the cotyledonary tissue upon infection, unlike susceptible forms. In YSPB-24, unlike Candle, distinct necrosis was visible at the site of infection as early as 5 days post inoculation (5 DPI). Light microscopic observations of trypan blue stained infected cotyledonary tissue revealed that the pathogen was able to germinate and penetrate the host tissue in both YSPB-24 and Candle, similar to susceptible accessions during the initial stages of infection. However, subsequent hyphal growth and penetration was restricted, with no significant growth seen beyond 3 DPI. In contrast, in the susceptible lines, hyphal growth was profuse, and increased with disease progression, culminating in pustule formation at 11 DPI. Hypersensitive response, as detected using DAB staining, was found only in the resistant accessions, YSPB-24 and Candle. Being completely resistant to A. candida, the two accessions identified in the present study would be useful resources for breeding durable resistance in B. juncea.
Key words: Albugo candida, Brassica rapa, resistance, white rust
*Author for correspondence: Priya Panjabi, e-mail: ppanjabi09@gmail.com
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