The accumulation of H 2 O 2 (oxidative burst) and the progress of pathogen development were studied in compatible and incompatible wheat-brown rust interactions. The accumulation of H 2 O 2 was detected in 98AE7% of guard cells with appressoria 8 h post inoculation (hpi). The reaction in both susceptible and resistant plants declined 2-3 days post inoculation (dpi). The second phase of the oxidative burst was observed in the mesophyll and ⁄ or epidermis. In susceptible plants it began 4-5 dpi and was detected only in the epidermis. In resistant plants the response was observed in the mesophyll. In moderately resistant plants it was induced 1-3 dpi, and the percentage of infection units reached 80-90% 8 dpi. This corresponded with severe necrotic symptoms. In highly resistant plants, the oxidative burst was short and transient. The percentage of infection units with H 2 O 2 accumulation reached its highest level (60-70%) 2 dpi, and decreased thereafter. Four days later, the low percentage and weak DAB staining indicated very low H 2 O 2 accumulation. The localization and the time-course changes of the oxidative burst correlated with the profiles of the micronecrotic response, haustorium mother cell formation and pathogen development termination. An early and localized induction of oxidative burst followed by its rapid quenching correlated with high resistance and almost no disease symptoms. The possible correlation of the oxidative burst and pathogen development patterns with the level and durability of resistance conferred by Lr genes are discussed.

Nineteen barley landraces collected from Morocco were screened for resistance to powdery mildew. The landraces originated from the collection at the Polish Gene Bank, IHAR Radzików, Poland. The fifteen landraces tested showed powdery mildew resistance reactions and 35 single plant lines were selected. Twenty‐one of these lines were tested in the seedling stage with 30, four lines with 17 and another 10 lines with 23 differential isolates of powdery mildew, respectively. The isolates were chosen according to their virulence spectra observed on the Pallas isolines differential set. Nine lines (E 1029‐1‐1, E 1042‐2‐2, E 1050‐1‐1, E 1054‐5‐1, E 1056‐2‐5, E 1056‐3‐1, E 1061‐1‐1, E 1061‐1‐3 and E 1067‐1‐2) which originated from seven landraces showed resistance to all prevalent European powdery mildew virulence genes. The most frequent score was 2 and 16 lines showed this reaction for inoculation with most isolates used. The distribution of reaction type indicated that about 77% of all reaction types observed were classified as powdery mildew resistance (scores 0, 1 and 2). In all lines the presence of unknown genes alone or in combinations with specific ones was postulated. Four different resistance alleles (Mlat, Mla6, Mla14 and Mla12) were postulated to be present in 10 tested lines alone or in combination. Alleles Mlat, Mla6 and Mla14 were postulated to be present in four and Mla12 in two tested lines, respectively. The value of barley landraces for diversification of resistance genes for powdery mildew is discussed.

Pathogenicity of 20 isolates of 12 Fusarium species recovered from triticale seed against seedlings of 14 varieties of winter cereals (triticale, wheat, and rye) was tested. The most pathogenic inoculum was a mixture of isolates (a composite isolate) of all the species. The following species were individually the most pathogenic: E avenaceum, E culmorum, E sambucinum var. coeruleum, and E graminearum. Winter triticale was more resistant to seedling blight than rye but more susceptible than wheat.Also reactions of 31winter and 12 spring varieties of cereals to head inoculation with a composite isolate of 4 Fusarium spp. ( E avenaceum, E culmorum, F. graminearum, and F. sambucinum var. coeruleum) was studied. In comparison to other cereals of similar type winter and spring wheat appeared to be the most susceptible while winter rye reaction was comparable to winter triticale. Spring and winter triticale varieties responded to head infection intermediately.There was no significant correlation between seedling and head reactions to infection with Fusarium spp. for winter rye and triticale. For winter wheat a negative trend was found. The above findings imply that screening of cereals at the seedling stage can not be used to predict the resistance to head blight. Nevertheless, resistance at the stage is highly desirable to prevent excessive damage of the crops due to the seedling blight incited by Fusarium spp..

No abstract

No abstract