Germinability of axenic uredospores of U. fabae isolates A and B was depended upon composition of growth media. Percentage of germination was higher in uredospores of younger than older cultures and it was inversed proportionally with spore concentration. Germination was better in2% than 4 or 6% of sucrose or glucose solutions in case of uredospores produced on MS-7 medium provided with extracts of broad bean leaves, meanwhile, uredospores formed on MS-7 medium alone germinated better in 4 and 6% glucose solution than the same concentrations of sucrose. Dikaryotic germ tubes, sprouted like yeast mycelium, oidiospores like-structures, germinated oidiospores, and infection structures i.e. appressoria, infection pegs, and infection hyphae were frequently observed during germination of uredospores. Isolates A and B were quietly varied in their abilities to hydrolyzing starch and liquefying gelatin as well as in activities of pectulolytic and cellulolytic enzymes secreted in liquid growth media. The highest activities of pectulolytic and cellulolytic enzymes were obtained at pH values 6 and 6.6, respectively. The activity of constitutive and induced pectulolytic and cellulolytic enzymes were higher in isolate A than isolate B. However, the ratio between induced and constitutive pectulolytic and cellulolytic enzymes of isolate A and pectulolytic enzymes only in isolate B were narrower in filtrates of 14 and 21 compared with filtrates of 7 days old cultures. The opposite trend was noticed, however, in isolate B. Under the IN VITRO conditions, the axenic uredospores of Uromyces fabae (Pers.) de Bary isolates A and B were able to infect both broad bean calli forming intercellular septate mycelium and oidiospores like structures and detached broad bean leaves forming oidiospores like structures in their epidermal tissues, however, under greenhouse conditions the typical rust pustule were frequently observed on inoculated leaves. Pathogenicity of iaolates A and B in relation to uredospore germination and activities of pectulolytic and cellulolytic enzymes was discussed. The isolate A produced few but larger concentric rust pustules surrounded by large numbers of minute pustules and clear yellowish halo zone meanwhile isolate B produced large numbers of smaller rust pustules without yellowish halo. |
