Secondary and Primary Plant Metabolites as Chemical Markers for Resistance of Bitter Candytuft (Iberis amara) Plant against Insect Attack

A correlation between the levels of secondary and primary plant metabolites and food coefficient parameters with the population density of infested broccoli plants was studied. Cucurbitacins and glucosinolates compounds were good signs of resistance in bitter candytuft plants. On the other hand, lower values or the absence of these markers rendered broccoli susceptible to the pests under study, not during all stages of growth but whenever these values were much lower throughout growth stages. The major cucurbitacins were isolated and purified from bitter candytuft and identified by spectroscopic techniques. Glucosinolates content in bitter candytuft was also studied. The development of cabbage aphid treated with various bitter candytuft extracts as well as isolated cucurbitacins was also evaluated. A field study showed a remarkable reduction (88.9 %) of cabbage aphid induced by spraying the broccoli plants with 4 % water extract after autolysis of bitter candytuft.