Pathogenicity to wheat seedlings of wheat-type and rye-type isolates of Pseudocercosporella herpotrichoides

Four groups of isolates of Pseudocerosporella herpotrichoides (wheat-type carbendazimsensitive, wheat-type carbendazim-resistant, rye-type carbendazim-sensitive and rye-type carbendazim-resistant) were tested for pathogenicity to wheat seedlings (cv. Armada), using mycelial or conidial inoculum. With either form of inoculum, wheat-type isolates usually produced more severe lesions than rye-type isolates, although the most pathogenic rye-type isolates were as pathogenic as the least pathogenic wheat-type isolates. Regressions of pathogenicity score on spore concentration (log10-transformed) were calculated for each of the four groups of isolates and showed that the data were best fitted by two lines with different slopes and different intercepts, one for the wheat-type isolates and one for the rye-type isolates.
Conidia of wheat-type isolates generally included a greater proportion of curved spores than those of rye-type isolates. There was little difference between conidia of the wheat-type and rye-type isolates in length, number of cells or ability to germinate, nor between carbendazimsensitive and carbendazim-resistant isolates of either wheat- or rye-type in pathogenicity or spore characteristics.