In certain years the fungus Erisyphe polygoni D.C., which is responsible for powdery mildew may heavily effect peas, especially dry peas. Some lines from Peru, Hawaii, and Geneva, U.S.A. as well as the varieties Mexique 4 and Stratagem show resistance to this disease. The resistance of the progenies from Peruvian material is confined to the leaves. The results of the investigations show that one recessive gene er1 can bring about full resistance in the field and in the glasshouse under Dutch conditions. The leaf resistance of the Peruvian lines is caused by a second recessive gene er2. The Dutch breeder could use in his resistance breeding work chiefly the variety Stratagem or the line SVP 942, which already possess the desirable straw length and seed colour. © 1969 Dr. H. De Haan.
