Plant Introductions of Zea mays as Sources of Corn Rootworm Tolerance

Over 2000 plant introductions of Zea mays</it> were given an initial screening under natural infestations of Diabrotica</it> spp. from 1962 to 1969. On the basis of the data obtained from the original screening, 441 varieties were selected for retesting at Dayton, Iowa, in 1970. Comparison of the field data for specific seed types disclosed that flour and dent varieties had the lowest average root damage ratings, the highest average number of secondary roots present, the greatest average height, and were, on an average, later manning. Dent seed types had the largest average root-size, and flour corn was significantly lower in average percent lodging. Rootworm resistance as expressed and measured in the field was believed to be mainly tolerance. The introductions that responded best to corn rootworm infestations were P.I. 177606, P.I. 239099, P.I. 214288, P.I. 177645, P.I. 303923, and P.I. 257625.