Six cultivars of peanut i.e. Giza 5, Giza 6, R92, Ismailia 1, Gregory and Virginia.
were evaluated for their susceptibility to the natural infection by Cercospora leaf spot during two
successive growing seasons of 2016 and 2017. Generally, Ismailia 1, followed by R92 were the most
resistant tested cvs., for the disease and produced the highest pod yield in both seasons. However,
Gregory, followed by Virginia were the most susceptible ones recording the highest percentages of
disease incidence and severity in tested both seasons. Induction of disease resistance was carried out
using salicylic acid, nicotinic acid, butyric acid, ascorbic acid and bion which were applied at three
concentrations, i.e. 2, 4 and 8 mM. The obtained results proved that bion and salicylic acid at 8 mM
followed by ascorbic acid at the same conc., were the most effective inducers for minimizing disease
incidence as well as disease severity and consequently increased the produced pod yield during both
investigated seasons . Four plant growth regulators namely indole butaric acid (IBA), naphthalene
acetic acid (NAA), gibberellic acid (GA3) and baclobtrazole were applied at three concentrations, i.e.
50, 100 and 200 ppm proved that naphthalene acetic acid and indole butaric acid at 200 ppm were the
most effective inducers for minimizing disease incidence as well as severity and consequently
increased the prodced pod yield during both investigated seasons. Four sulfate mineral salts i.e.,
copper sulphate (CuSo4), zinc sulphate (ZnSo4), magnesium sulphate (MgSo4) and manganese
sulphate (MnSo4) at three concentrations, i.e. 1, 2 and 4mM, were tested. Copper sulphate followed by
magnesium sulphate gave the lowest percentages of disease incidene and severity without significant
differences in between and consequently increased the produced pod yield. The effect of five silicate
salts, i.e. calcium silicate (CaSio3), magnesium silicate (MgSio3), potassium silicate (K2Sio3)
aluminum silicate (Al2Sio3) and seal- matreax (commercial compound) at four concentrations, i.e. 200,
400, 800 and1600 ppm were evaluated. Generally, calcium silicate followed by potassium silicate
gave the lowest percentage of disease incidence and severity and increased the produced pod
yield.Thus, there is a correlation between induced resistance and some biochemical changes in peanut
leaf tissues including phenol contents (free, conjugate and total phenols) and oxidative enzyme
activities, i.e., peroxidase and polyphenoloxidase.