Modeling parasite; host: environment specificity
1989
Shehab El-Din, T.M. | Browder, L.E. (Field Crops Research Inst., Giza (Egypt). Wheat Research Section)
Specificity is a well-known phenomenon in many parasite: host systems. Many investigators have modeled specificity in one environment, assuming that environment has no effect. A Boolean algebraic approach to modelling specificity was proposed. Parasite and host come together to form a third entity, the aegricorpus. A definitive parasite genotype interacts with a definitive host genotype to produce a definitive aegricorpus genotype that functions in a definitive environment to produce a definitive phenotype. The definitive phenotype results in resistance in some cases and susceptibility in others. Nondefinitive at one or more of the variables results in a nondefinitive phenotype. The basic model and its expansion illustrate different characteristics of the specificity system. Six different formulae are used to calculate the parameters - number of individuals, number of aegricorpus genotypes, number of phenotypes, number of individuals with a given definitive phenotype, number of individuals with nondefinitive phenotype, and expected ratio of phenotypes. The basic model and its expansion confirm the importance of genetic diversity where definitive phenotypes result in resistance. The frequency of definitive genotypes increases with increasing number of sets of corresponding gene pairs, regardless of other variable. Partial function of definitive aegricorpus genotype in a nondefinitive enviroment is the likely basis of "horizontal resistance" and "slow rusting/blasting". In many parasite: host systems, the aegricorpus phenotype behaves like a quantitative character. It is controlled by many sets of corresponding gene pairs and is greatly influenced by environment. Thus it can be studied quantitatively.
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