H.S.S. Sharma

Relationship of spore germination and appressoria formation in isolates of Septoria nodorum to pathogenicity on wheat and barley leaves

A wheat isolate (WI 1 ) and one barley isolate (BI 1 ) of Septoria nodorum showed little change in pathogenicity after one passage through the opposite host, but after two or three passages some loss in pathogenicity to the original host was observed. Some re-isolates of a second barley isolate (BI 2 ) showed morphological characteristics typical of wheat isolates after a single passage through wheat, and after a second passage through wheat a morphologically changed barley re-isolate was as pathogenic on wheat as the original wheat isolate and showed poor pathogenicity on barley; repeated passage back through barley failed to reverse this effect. Spores of WI 1 germinated to a similar extent in both wheat and barley leaf leachates, as did BI 2 , but spores of WI 1 tended to germinate more rapidly. The proportion of germinated spores of WI 1 and BI 2 producing appressoria was, however, greater in leachates from wheat leaves. Germination in both isolates was similar on the surface of wheat and barley leaves during the first 6 h incubation, although after 24 h incubation a higher percentage germination was observed on the original host. Hyphae of WI 1 were considerably more branched on wheat leaves than on barley leaves while hyphae of BI 2 were more branched on barley leaves. Hyphae of the morphologically changed barley re-isolate (BI 2 ) were more branched on wheat leaves. Appressoria were produced at the tips of most hyphal branches of all isolates.

Temperature enhanced sectoring in barley isolates of Septoria nodorum and the possible relationship with varying pathogenicity

Sectoring was enhanced in cultures of some barley isolates of Septoria nodorum by increasing the incubation temperature several degrees above the growth optimum for short periods. The new type of growth in the sectors was not stable and reverted back to the original in subcultures grown at the optimum temperature. Spores from the sectored zones in the cultures were often more pathogenic on barley than the original isolate although the differences were not statistically significant and isolates which sectored adapted much more readily to wheat with corresponding loss of aggressiveness on barley than isolates in which sectoring could not be induced.

Spoilage of flax straw by Ceraceomyces sublaevis

Ceraceomyces sublaevis rotted inadequately dried flax straw. The fungus was not highly cellulolytic and xylanase, a constitutive enzyme of the organism, apparently played a major role in degradation of flax fibre.