How do plants perceive environmental stress ? Biotic and abiotic stress induces plant response and before" dying" different levels of resistance is shown and finally plants are overcome with stress depending their level of genetic composition, environmental condition and strenght of the attacker.
All efforts to arm the plants with constitutive or dynamic resistance are based on early perception and response to the attacker. Plants have some kind of "anti ballistic missile" or defence system which gets activated at the earliest and the "attacker"  is checked out or its effects mitigated for the time being . Some time it happens by hypersensitive reactions . Immediate death of the attacked cell and capcization of attacking pathogen. However how do plants perceive the signal for quick response. You will be surprised to note that its the plants which have recongition site for pathogens plant cell membranes have specific protiens or membranous configurations and pathogens recognise such sites . That could be what makes biotrophic or obligate pathogens to make precise attack on specific plant species and leaving all others unattacked. However this facility is not provided to the necrotrophic pathogens or facultative parasites. Are there specific mechanisms to combat biotic stress also. Besides pathogens also have mechanisms to overcome resistance provided to the plants by plant breeders and develop their races which are more violent .
Man has learned from plants or plants have learned from man. Obviously plants came first.
Protect plants to keep man alive.