The possible involvement of lipoxygenase in downy mildew resistance in pearl millet

Abstract

The downy mildew disease, incited by Sclerospora graminicola, is a major biotic constraint for pearl millet production in the semi-arid tropics. Sources of resistance to this disease have been identified. However, the mechanism of host resistance still remains obscure. The enzyme lipoxygenase (LOX) is known to play a role in disease resistance in many host-pathosystems. In the present study, LOX activity was tested in seeds of different genotypes of pearl millet with different susceptibility to downy mildew. The LOX assay of the seeds indicated a good correlation between enzyme activity and their downy mildew reaction in the field. Maximum activity was recorded in seeds of highly resistant genotypes and minimum activity was found in the highly susceptible genotypes. Seeds obtained from plants recovered from the downy mildew disease had more LOX activity than that of the original parent seeds. Thus, in seeds, the LOX activity can be used as a biochemical marker for screening different genotypes of pearl millet for downy mildew. The study, carried out in the susceptible genotype of pearl millet seedlings, showed that LOX activity decreased after inoculating with S. graminicola zoospores when compared with uninoculated controls. However, a significant increase in the enzyme activity was observed on the second and third days after inoculation in resistant seedlings. The possible role of LOX in conferring resistance to downy mildew infection of pearl millet is discussed.