Some factors affecting the relative ability of two strains of Puccinia graminis tritici to survive when mixed

Abstract

The process of infection by strains 21 Anz-2, 7 and 21 Anz-2, 3, 7 of Puccinia graminis tritici was quantitatively investigated to determine whether differences existed between them at any stage of the infection process and whether any such differences were related to the relative survival ability of the two strains in mixtures. The frequency of urediospore germination, the frequency of formation of appressoria, the period between inoculation and the eruption of uredia, the proportion of infection courts developing into uredia, and the visible characteristics of the uredia, did not differ between the two strains. However, penetration occurred more frequently from appressoria of strain 21 Anz-2, 3 , 7 than from those of strain 21 Anz-2, 7. Uredia of strain 21 Anz-2,3,7 increased more rapidly in size than did thoseof 21 Anz-2,7 and were ultimately larger in area. Similarly, more urediospores were produced per uredium by strain 21 Anz-2, 3, 7 than by 21 Anz-2, 7. It is suggested that these differences in frequency of penetration and in number of urediospores per uredium could account, at least in part, for the difference in relative survival ability between the two strains.

Relative survival ability in a polycyclic system of Puccinia coronata avenae monosporic isolates in biracial mixtures on universal oat suscepts

“…Brush inoculation also has proven adequate to cycle P. graminis avenae (Martens, 1973) and P. graminis tritici (Ogle and Brown, 1970).…”

“…After m cycles or generations, the proportion of race 1, and that of race 2,7^=1-?^, can be calculated. Ogle et al (1973) found a very good fit of the model to data obtained by Ogle and Brown (1971) on components of reproductive rates for two strains of P. graminis tritici isolated from the Australia-New…”

“…In laboratory studies where stresses from host and environment are minimized, instability of heterogeneous populations has been confirmed for P. recondita tritici (Aslam and Browder, 1971;Irish, 1950), P. striiformis (Brovm and Sharp, 1970), P. graminis tritici (Loegering, 1951;Ogle and Brown, 1970;Watson, 1942), P. graminis avenae (Leonard. 1969a: Martens, 1973, and P. coronata avenae (Bustamante, 1972 …”

“…For the wheat stem rust fungus, P. graminis tritici. Ogle and Brown (1971) reported yields of 61,100 spores/uredium.…”

“…Ogle and Brown (1970) acknowledged that the declining component race ANZ 21-2,7, in mixture with race ANZ 21-2,3,7 of P. graminis tritici, remained in the rust population at low levels. Interactions of the nature I have described may explain the persistence of declining components in a heterogeneous population.…”