The effect of applying exogenous salicylic acid on aphid infection and its influence on histo-physiological traits and thermal imaging of canola

Insect damage in canola adversely affects its productivity and quality and is considered one of the most important degrading factors in Egypt. The effect of foliar application of salicylic acid (SA) on aphid populations, growth and yield of canola (Brassica napus, L.) cv. serw 4 was the major goal of this study. Two experiments were conducted at the farm of Faculty of Agriculture, Suez Canal University, Ismailia, Egypt, during 2014 and 2015 seasons, to achieve this target. Each experiment included four levels of SA (0, 50, 100, 200 mg l-1). The experimental results revealed that SA, at low concentration (50 mg l-1), was an effective treatment for reduction the number of aphid populations and colony depth on the main inflorescence, contributed with reducing the thickness of secretory tissue of flower pedicel. The level of 50 mg l-1 of SA-treated canola had the highest number of stomata cm-2, along with the lowest width of both stoma and its aperture. Thickness of xylem tissue and the number of xylem vessels bundle-1 in leaf midrib, reducing sugars and free amino acids was increased at 50 mg l-1 SA, but free phenolics content did not affected significantly. Under controlled conditions, changes in temperature of infected leaves allowed the discrimination between healthy and infected areas in thermo-image, even before visible symptoms of aphid infestation appeared. The detection of modifications in plants or canopies, associated with low insect severity in the early stages of infestation, was crucial for the targeted, site-specific or on demand application of integrated aphid control. Canola, which was treated with 50 mg l-1 of SA, gave 30.5 and 27.9 kg of oil ha-1 over the control. It was concluded that spraying of SA at 50 mg l-1 was an effective elicitor to diminish the aphid numbers on canola inflorescence and improve its yield