Dr. Lawaju, you cannot categories the population like this. It  depends on the type of crop , environment and effective population as well as defense mechanism of the -plants. You need lot of experiments to generalize the things like you mentioned. Disease outcome is determined by the three-way interaction of the pathogen, the plant and the environmental conditions. Defense activating compounds can move cell-to-cell and systematically through the plant vascular system. A gradation of quantitative difference in disease resistance is more typically observed between plant strains or genotypes. The disease resistant mechanism depends on: plant cuticle/surface, plant cell walls, antimicrobial chemical (glucosides, saponins etc.), antimicrobial proteins, enzyme inhibitors, detoxifying enzymes that break down pathogen-derived toxins, receptor that perceive pathogen presence and activate inducible plant defense as well as immune system of plants. Thats why to generalize the thing with only pathogenic microbial population is very difficult.

Hello Bisho Lawaju

I suggest to read this book "Plant Disease: An Advanced Treatise, 

Editors: James G. Horsfall" .  You can find a very good details about disease resistance.

Good luck

Thank you Dr. J. C. Tarafdar and Dr. Jawad K. Abood Al-Janabi. I will take your suggestions in my mind.