COMPARISON OF THE WHEAT BROWN AND YELLOW RUSTS FOR MONOCYCLIC SPORULATION AND INFECTION PROCESSES, AND THEIR POLYCYCLIC CONSEQUENCES

Sporulation capacity and infection efficiency of wheat brown and yello w rusts were measured daily in favourable controlled conditions. Monoc yclic sporulation capacity for a single lesion of yellow rust was 9 ti mes greater than for an isolated lesion of brown rust, and 40 times gr eater than for a lesion of brown rust at medium infection density. Inf ection efficiency fluctuated and reached about 40 % for brown rust but remained under 5 % for yellow rust. For both fungi, sporulation capac ity and infection efficiency compensated for each other, but their pro duct, the daily multiplication factor, was greater for yellow rust tha n for brown rust. Progeny/parent ratio was 3 times greater for yellow rust. Effect of daily multiplication factor variations on epidemic pro gress was simulated using a simple matrix model. Increase in number of lesions was faster in brown rust than in yellow rust because of a lat ent period shorter by 2 days. Semi-systemic growth of yellow rust fung us reduced, however, the difference between both fungi when sporulatin g surface was calculated.