Chapter 32, Problem 1QC

Summary Introduction

To explain:

Whether the specific component of the plant immune system (the one using R genes) can defend against both biotrophic and necrotrophic pathogens or not.

Concept Introduction:

“Biotrophic pathogens” are those organisms which obtain the food by infecting the living cells. “Necrotrophic organisms” are those organisms that degrade and destroy the living cells before obtaining food from them.

Explanation of Solution

$R$ genes are specific genes of the plant immune system which protect the plant from the attack of the pathogens. These genes synthesize the $R$ proteins which react with the AVR protein to form a complex. This protects the immune system of the plant from the attack of the pathogens.

$R$ genes can protect the plants from the action of the biotrophic pathogens only and not the nectrotrophic organsims, because these infect the living cells and not the dead cells. The examples of biotrophic organisms include wheat leaf rust fungus “Puccinia” and the necrotrophic organism includes the rice blast fungus “Magnoporthe grisea”.

Conclusion

No, the specific component of the plant immune system consists of the $R$ genes which protect the plants infected from the biotrophic pathogens and not the necrotrophic pathogens.