Epidemiology of wheat rusts in the Western Hemisphere

AND THE PRAIRIE PROVINCES OF CANADA), PROMPTED THE STUDY OF PHYSIOLOGIC SPECIALIZATION IN STEM AND LEAF RUST, THE BREEDING OF RESISTANT VARIETIES, AND THE EPIDEMIOLOGY AND AEROBIOLOGY OF THESE RUST DISEASES. NO COMPARABLE AREA OF THE WORLD HAS BEEN STUDIED SO PRECISELY AND 50 YEARS DATA HAVE BEEN SYSTEMATICALLY PRESENTED FOR THE AEROBIOLOGY AND EPIDEMIOLOGY OF THESE ORGANISMS IN THIS REGION. IN THE PRESENT PAPER, ADDITIONAL EVIDENCE IS PROVIDED TO SUPPORT THE HYPOTHESIS THAT THIS REGION FORMS A SINGLE EPIDEMIOLOGICAL ZONE FOR THESE TWO DISEASES. FIVE OTHER MAJOR GEOGRAPHICAL EPIDEMIOLOGICAL ZONES ARE DELINEATED IN THE WESTERN HEMISPHERE: THREE IN NORTH AMERICA AND TWO IN SOUTH AMERICA. EVIDENCE FOR THEIR EXISTENCE IS BASED ON DATA AVAILABLE FOR VIRULENCE PATTERNS OF THE THREE SPECIES VIZ PUCCINIA GRAMINIS TRITICI, PUCCINIA RECONDITA AND PUCCINIA STRIFORMIS, EITHER OF ONE OR A COMBINATION OF SPECIES. EPIDEMICS, VIRULENCE SURVEYS, VIRULENCE PATTERNS ON VARIETIES IN FIVE INTERNATIONAL SPRING WHEAT YIELD NURSERIES AND TWO YEARS OF THE INTERNATIONAL STRIPE RUST NURSERY, HAVE BEEN USED TO PROVIDE SUPPORTING DATA INDICATIVE OF REGIONAL GROUPINGS.