ARACHIDONIC ACID-INDUCED HYPERSENSITIVE CELL-DEATH AS AN ASSAY OF DOWNY MILDEW RESISTANCE IN PEARL-MILLET

Arachidonic acid (AA) induces hypersensitive response (HR) on coleopti le/root regions of two-day-old pearl miller seedlings. The response is comparable to the HR induced by the downy mildew pathogen, Sclerospor a graminicola. A time gap in the appearance of cell necrosis among gen otypes of pearl millet was related to the degree of resistance to down y mildew. Based on the time required for the development of necrotic s pots induced by AA, the pearl millet genotypes were categorised as hig hly resistant/resistant (HR in 3-6 h), susceptible (HR in 7-12 h) and highly susceptible (HR in 13 h and above). The percentage disease inci dence in each genotype was compared with the time required for the dev elopment of AA-induced HR. The appearance of hypersensitive cell necro sis was rapid in genotypes having high resistance to downy mildew and was slow in genotypes with high susceptibility. This simple method of screening various pearl millet genotypes in the absence of the pathoge n aids in identifying the downy mildew resistant/susceptible host cult ivars without the risk of introducing the virulent race of the pathoge n.