ABSTRACT
Koch’s postulates are the gold standard to establish the etiological relationship between a putative pathogen and its host. They were formulated to ensure that scientific rigor is applied when proposing a potential microbe/infectious agent as a pathogen for a specific disease. These guidelines resulted in the theory of one pathogen–one disease, and as a tangential consequence, mono-microbial causation predominated disease causation studies. Their credibility was questioned when viruses, obligate parasites, latent infections, synergism, and poly-microbial infections were discovered. In due course, the development of DNA technologies led to the discovery of virulence genes, which resulted in Molecular Koch’s postulates. Genetics and cloning technologies equipped scientists to isolate a putative virulence gene and evaluate its pathogenicity to fulfill Molecular Koch’s postulates. Pathogen and host continuously switch their genes on and off to achieve desirable phenotypes. Redundancy and robustness of effector and plant immunity genes explain that pathogen–host interaction results in various cross talks and counterattacks. Hence, an inclusive approach—system biology—is applied to understand qualitative and quantitative plant–pathogen association by integrating high throughput data, computational resources, and machine learning. However, system biology models for plant–pathogen interaction are in their infancy and require serious attention and resources. These system biology–based models can help balance the trade-offs between plant immunity and growth, crucial for sustainable agricultural production and food security.
