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Evaluation of 10 Generations of Mass Selection for Corn Earworm Resistance¹

Mass selection for resistance to corn earworm (Heliothis zea (Boddie)) was made in two corn, Zea mays L., populations (Synthetics C and S) grown in isolation for 10 generations during the period 1956 to 1965. Plantings were made on or about 15 June to enhance the chances for a high infestation of earworm. From each planting at least 1,000 ears were classified into three categories: (1) penetration of the earworm to the kernel resulting in damage, (2) earworm entry into the silk channel but no kernel damage, and (3) no evidence of earworm entry into the silk channel. Ears from class 2 were used for planting the subsequent cycle

In 1965, remnant seed of five cycles (spanning the 10 generations) for each synthetic was increased by sibpollinating approximately 200 plants. Evaluation tests were grown at two locations in 1966.

Mass selection in both synthetics was effective. for Synthetic C the percentage of ears with kernel damage was reduced from 80.8% (1957) to 58.7% (1965), a reduction of 2.76% per generation. The percentage of ears with earworm damage for Synthetic S was reduced from 64.5% (1956) to 39.2% (1965). The average reduction per generation was 2.81%

Key Words: Heliothis zea (Boddie) • Zea mays L. • Synthetics

² Research Agronomist. CRD, ARS, USDA, and Professor of Agronomy; Professor of Entomology; Assistant Professor of Entomology; formerly Assistant Professor of Field Crops (now Specialty Plant Breeder, Bear Hybrid Corn Co.); Associate Professor of Statistics; Instructor of Statistics; and Research Geneticist, CRD, ARS, USDA and Assistant Professor of Agronomy, University of Missouri Agricultural Experiment Station, Columbia, Missouri 65201.

Received for publication February 24, 1970.