Variability of uredial cultures of Puccinia graminis tritici derived from 'vegetative' axenic mycelium

Abstract

Two of 26 'vegetative' axenic cultures of Puccinia graminis tritici were induced to infect wheat by the epidermal stripping and mycelial implant technique. Only one of these two cultures produced urediospores and could be propagated on wheat. The urediospores obtained from implants had poor infectivity and there was a long incubation period. Single pustule isolates varied in growth rate, colour, virulence, sporulation, pustule type, and number of nuclei per spore. The uredial cultures comprised two groups: (1) one group with dikaryotic spores which resembled the parent culture race 126-Anz-6,7, Sydney University No. 334; (2) another group with monokaryotic spores which varied widely. The variability of the uredial cultures is interpreted as evidence that the diploid nucleus of the 'vegetative' axenic cultures originated by fusion of two haploid nuclei and divided in two ways: firstly, by a reduction division that produced two haploid nuclei and reconstituted a dikaryon similar to race 126-Anz-6,7, and secondly, by a mitotic division that produced diploids, variant aneuploids, and possibly mitotic recombinants.