Nirmaljit KaurChhabra, Rohit2019-11-122019-11-122019http://krishikosh.egranth.ac.in/handle/1/5810135080The present study to understand the basis of disease tolerance in rice cultivars was performed on two aromatic (PUSA 1121 and PUSA 1509) and two non-aromatic (PR 121 and PR 126) cultivars in field area, laboratory of Department of Botany and Seed Pathology laboratory, Punjab Agricultural University, Ludhiana (Punjab). The seeds of the experimental rice cultivars were inoculated with virulent isolate of Fusarium fujikuroi obtained from seed Pathology laboratory. The first experiment was to study the biochemical and anatomical traits associated with development of bakanae in seedlings under laboratory conditions. The second experiment dealt with the field reaction and associated metabolic changes in nursery grown seedlings. The third experiment was further divided in two sections, firstly to study the effect of inoculation of rice seeds with F. fujikuroi on their vigour, and the second part highlights the variation in biochemical machinery of the rice seeds 48 hours after inoculation. Reduction in percent germination and fresh and dry weight of seedlings was observed in both aromatic and non-aromatic rice cultivars post inoculation, the variation being significant in aromatic cultivars. Seed inoculation with the fungus resulted in a significant increase in length of the infected seedlings in aromatic rice cultivars as compared to non-aromatic ones possibly due to significant enhancement of endogenous gibberellic acid post infection in the aromatic rice seedlings. The chlorophyll a, b and total chlorophyll, total soluble sugars and starch content was higher in healthy seedlings, while carotenoids and alpha amylase activity was higher in infected seedlings of both aromatic and non-aromatic rice cultivars. Total phenols, orthodihydric phenols and total soluble proteins were higher in non-aromatic rice seedlings post infection indicating the initiation of defence mechanism against the pathogen. Increase in activity of peroxidase, superoxide dismutase, polyphenol oxidase and antioxidant activity in aromatic rice cultivars post infection indicate the biotic stress created by pathogen. Histopathological observations revealed hyphal and conidial growth in infected tissues of aromatic cultivars whereas a complete and intact tissue was observed in healthy and infected counterparts of non-aromatic cultivars. The induction of activity of antioxidant enzymes in aromatic rice seeds post inoculation could be effectively exploited to screen the tolerance potential of aromatic rice cultivars against bakanae disease.ennullThesis