Wheat Powdery Mildew Investigations

The development of Erysiphe graminis f. tritici Em. Marchal, from spore germination to spore formation, occupied 6 days and ascospore discharge in the field covered a period of i month. On immune hosts development of the fungus generally ceased at the point of invasion of cell cytoplasm. The features of host plant resistance have been discussed. Lithium chloride soil applications were made as o‐8% solution in glasshouse seedling plant experiments and at 56 lb./acre rate in a factorial field trial. In the former, mildew was reduced from 11% leaf area infected to 1 %, but under field conditions only from 1–29 to 1–04% over two sampling periods. The limiting effects of lithium on mildew began to decline 18 weeks after soil treatment. Race 4 of E. graminis f. tritici (Canadian typing) was present in all, and Race 3 in about half the New Zealand wheat localities during 1948‐9. The infection types of Races 3 and 4 on 180 wheat varieties and breeding selections have been recorded, and the basis for a mildew resistance plant‐breeding programme is discussed, including consideration of adult plant resistance.