Determination of Molecular and Biochemical Changes in Cotton Plants Mediated by Mealybug

• Cotton mealybug injury causes phenolics accumulations in xylem associated cells.
• Insect injury alters the quantity of few defensive biochemicals, according to the type of modified plant metabolic pathway.
• Elevated enzyme activities recorded in cotton plants after insect attack, which were interlinked with strengthening of physical barriers.
• Thaumatin-like gene expression was found to be connected with mealybug attack on cotton.
• Although, expression of pathogenesis related genes was enhanced due to insect attack; but no strictly direct relationship was found between expression of PR-genes and synthesis of defensive biochemicals.

Phenococcus solenopsis (cotton mealybug) is a devastating insect pest of many countries of the world including Pakistan. Due to its piercing sucking type feeding behavior, it injures cotton plants mechanically and induces several cytological and physiological changes in the host. These changes have been studied after subjecting healthy plants with mealybug under controlled conditions and it was recorded that mealybug attack enhanced lignin, cellulose and hemicellulose contents remarkably. It was also observed that defensive biochemicals of cotton i.e. phenolics and terpenoids were also significantly increased (up to 7 times) with progressing time (0-3 hr) in injured plants. Defensive enzymes i.e. phenyl ammonia lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD) also showed direct relationship with the passing time (0-3 hr) after mealybug feeding. Similarly, expression of thaumatin-like, metallothionein and profilin genes was enhanced with the elicitation of plant defenses due to insect herbivory. There was no connection found between pathogenesis related Pseml gene and plant defense against herbivory. Study concluded that mealybug did not modulate all plant defenses. There were specific biochemicals and defense related genes influenced by the attack of mealybug.