RACE DIVERSITY AND COMPLEXITY IN SELECTED POPULATIONS OF FUNGAL BIOTROPHIC PATHOGENS OF CEREALS

The relationships between several variables (sample size, measures of race number and frequency, number of discriminant differential hosts) and mathematical estimates of race diversity and complexity were studied by means of linear correlation and principal component analysis in various populations of cereal biotrophic pathogens, using race survey data from the literature. No constant relationships between the variables studied were found in geographically distinct populations of several rust and powdery mildew pathogens of cereals, suggesting a large local effect of selection by resistance genes on race diversity and complexity in these populations. Diversity estimates based on race abundance, race dominance, or synthetic indexes were generally correlated, irrespective of the population considered; no clear correlation was found between estimates of diversity and complexity. The increase in virulence complexity in rust pathogens and stability of complexity at a low level in powdery mildew fungi as new genes are introduced in the host population are possibly related to the biology of the pathogens considered, and particularly the presence or absence of a sexual phase. The large incidence of the characteristics of the differential set used on recognized diversity and complexity patterns is shown and discussed.