Chhabra, GurinderSandhu, P.S.2018-01-122018-01-122017http://krishikosh.egranth.ac.in/handle/1/5810039275White rust caused by Albugo candida is one of the most widespread and destructive disease of rapeseed-mustard causing serious threat to its production. The present studies entitled “Population structure of Albugo candida (Pers.) Kuntze inciting white rust of rapeseed-mustard” were carried out to determine the variation in the pathogen in Punjab state. Isolates of A. candida were collected from different rapeseed-mustard growing areas of Punjab state. A total of 8 districts (Bathinda, Barnala, Faridkot, Muktsar, Mansa, Moga, Ludhiana and Fazilka) were surveyed and 71 isolates were collected from these locations. Disease incidence and severity on different varieties was recorded during crop season 2015-16 and 2016-17. Disease incidence and severity was higher during 2015-16 which ranged from 37.60-64.52 and 21.29-27.45 per cent as compared to 22.52-52.12 and 11.86-22.68 per cent in 2016-17. Highest disease incidence and severity was recorded in Bathinda followed by Mansa and Barnala whereas Fazilka recorded lowest. Highest disease severity was recorded on PBR 91 while lowest on PBR 357. Among the isolates when inoculated on B. juncea var. RL1359, 57 isolates produced similar and stable symptoms, while 14 isolates did not reproduced true to type reaction. Isolates were categorized morphologically on the basis of pustule shape, size and color into three groups viz. AC I, AC II and AC III. Representative isolates were selected from respective groups to study virulence pattern on the basis of disease reaction along with their incubation period, number of pustules, size of pustules, number of sporangia and per cent germination of sporangia. Nine cultivars of the 6 different Brassica sps. were used as host differentials for these isolates. None of the isolates could produce symptoms on B. juncea (RLC 3), B. carinata, B. napus, B. rapa (Toria) TL 15. All the three groups produced symptoms on B. juncea (RL 1359, Varuna, PBR 91) while only group AC III could produce symptoms on B. nigra and B. rapa. Isolates showed considerable variation w.r.t. size of pustules, number of sporangia and percent germination of sporangia with highest in AC III followed by AC I and least in AC II respectively. The incubation period was in range of 7-10 days with 7 on the most susceptible variety RL 1359 and 9-10 days on least susceptible FRG 2 and PT 303 respectively. Genetic characterization was carried out using a set of fourteen SSR primers. With cluster analysis at similarity coefficient of 0.15, isolates were clustered into two main groups with Group 1 and Group 2. Studies on morphological, pathological and genetic level showed that AC III group is most virulent and AC II group is least virulent. Within AC III group, Ac32 and Ac 54 isolates were recorded as more virulent than other isolates and these two isolates were distinct genetically from each other. So it is concluded that there exist some variations among isolates at morphological, pathological as well as genetic level in Punjab.ennullThesis