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Inheritance of Husk Numbers and Ear Insect Damage in Maize¹

Studies were made to determine the extent and genetic control of husk number variations in maize (Zea mays L.), and to test their association with ear insect resistance and response to environmental influences. Husk numbers were highly uniform within inbreds and single-cross hybrids, ranging from 6 to 19. Twelve inbreds were chosen to represent this range for diallel and generation-mean analyses. Analyses were made in Cali, Colombia, and in Waimanalo, Hawaii, of husk numbers from I0- and nine-parent diallels. General combining ability (g.c.a.) mean squares were highly significant at both locations. Specific combining ability mean squares were also significant, but were exceeded by the g.c.a, values by ratios of 5.3 to 1 (Colombia) and 19.9 to I (Hawaii). Hybrids showed a significant positive heterotic effect of 11%, and array means correlated well with parental values (r = 0.93). Means and array means for the hybrids grown at both locations were also highly correlated (r = 0.94 and r = 0.86, respectively). F₂ and backcross progenies of 10 crosses involving high x low husk numbers were analyzed. Backcross progenies commonly reverted sharply toward parental means, and F₂ and F₁ means were quite similar. Environmental variability was high and narrow-sense heritability estimates were low (average 24%). The Cuban Flint-derived inbred CM111 (India) provided the best genetic source for increasing husk numbers, which is proposed as a practical and efficient alternative to selection for low insect injury for improved ear pest resistance.

Damage by the larvae of ear insects was evaluated for earwonn (Heliothis zea Boddie) and fall armyworm [Spodoptera frugiperda (J. E. Smith)] in relation husk numbers in Hawaii and Colombia. Resistance was notably higher in tropical lowland types of maize with high husk numbers. Ear damage in Hawaii (largely earworm) correlated significantly (r = –0.40) with husk numbers that ranged from 6 to 14 in a broad-based composite. Ear insect damage in Colombia (largely fall armyworm) also correlated significantly (r = –0.68) with husk numbers that ranged from 8.0 to 14.9 in a 45-entry diallel. Husk numbers were highest for lowland tropical races of maize and lowest for temperate and montane races, correlating significantly (r = –0.71) with elevation at which the race was indigenous. It was concluded that ear pests provided strong selection pressure for higher husk numbers during evolution of maize. Environmental effects on husk numbers appeared solely to relate to temperature during growth, and a reduction of one husk was observed for a corresponding increase of 4 C in growing temperature during early growth.

Key Words: Zea mays L. • General combining ability • Insect resistance • Heliothis zea • Spodoptera frugiperda

² Professor of horticulture and genetics, Univ. of Hawaii, Honolulu, HI 96822, and maize breeder, Office of Rural Development, Suweon, Korea.

Received for publication August 22, 1977.