| Analysis of primary infection and host response of
wheat to powdery mildew fungus Masataka MORITA Laboratory of Genetics, Faculty of Agriculture, Kobe University, Kobe The six-day old seedlings of 24 different strains of wheat and their hybrids were inoculated with the conidiospores of wheat powdery mildew fungus, Erysiphe graminis f. sp. tritici, race t2. The number of germinated spores with the elongated secondary hypha (ESH) of more than 12.5 micro in length was counted with time until 32 hours after inoculation and expressed as ESH % (a ratio in percent of the spores with ESH to the spores with matured appressorium). Further examination of the fungus development and host response was made until 6 days after inoculation. There observed four types of resistance in the host plants to fungal infection. The first was a type of strong protection to the invasion of the fungus into the host epidermal cell. The spores were able to germinate and form appressoria, but fail to form haustorial bodies. Triticum dicoccoides var. spontaneonigrum and a variety of T. dicoccum (No. 189) were recorded as this type. The second was a type exhibiting an abnormal development of haustorium. The spores were allowed to grow and form haustorial bodies, but their growth ceased and then the secondary hypha was not formed. T. dicoccum var. atratum (No. 122) was recorded as this type. The third was a type, in which the mycelial growth was inhibited within 2-3 days after inoculation. The spores having ESH were approximately 5%. T. monococcum var. vulgare and T. pareocolchicum var. shwamilicum were recorded as this type. The fourth was a type which formed a few pustules. The earlier process of infection looked like to that of the third type, however, some of the spores finally grew into maturation and a few pustules were visible at 6 days after inoculation. T. aestivum var. pseudoingrediens was recorded as this type. The remaining 18 strains were fully susceptible, in which many pustules were observed on the leaves at 6 days after inoculation. The genetical analysis on 21 F2 hybrids and 6 F2 populations suggested that two recessive genes were involved in the expression of the first type of resistance and a dominant gene in the second and third types of resistance, respectively. |