Fundamentals of Plant Pathology

INTRODUCTION

Variability means the quality of being subject to variation or quality of being uneven or lacking uniformity. In plant pathogens, the variation takes place due to genetic variability. Genetic variability is the measure of the tendency of individual genotype in a population to vary from other or having more than one genetic state or allele at each locus.

• Variation is usually associated with sexual reproduction by fungal oospores, zygospores,
• a variant can be defined as an individual among a certain population that have deviated from the normal individuals genetically and possesses certain different characters which are not generally associated with that particular population previously.

Mechanisms of variability in plant pathogens

• General mechanisms of variability are:

- mutation, recombination, gene and genotype flow, genetic drift and selection, out-crossing etc.

• Specialized mechanisms of variabilityare:

- heterokaryosis, parasexuality, saltation etc. in fungi
- conjugation, transformation and transduction in bacteria
- recombination in viruses