Germinability of axenic uredospores of U. fabae isolates A and B was
depended upon compsition 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 in 2% 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 likestructures,
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 quitely 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. |
