Association of lignification and callose deposition with host cultivar resistance and induced systemic resistance in pearl millet to Sclerospora graminicola

Histochemical studies on pearl millet (Pennisetum glaucum) seedlings responding to invasion by the downy mildew pathogen Sclerospora graminicola strongly suggested that lignin and callose deposition were host structural responses for cultivar resistance. A time-course study showed that the accumulation of the polymers in cell walls of resistant (cv. IP 18293) seedlings was rapid and localised around the pathogen, apparently to restrict pathogen entry. Regression analysis indicated a longer time requirement for such cell wall deposition in seedlings (cv. HB3) susceptible to the downy mildew pathogen. Interestingly, susceptible pearl millet seedlings induced for systemic resistance against S. graminicola using aqueous leaf extract of Datura metel also showed host reactions similar to that observed in seedlings showing cultivar resistance to the pathogen. These results suggested a similarity in the structural resistance responses in induced systemic resistance and host cultivar resistance of pearl millet against the downy mildew pathogen.[PUBLICATION ABSTRACT]