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Diallel Analysis of the Photoperiodic Response of Maize¹

A diallel cross from eight early maturing maize (Zea mays L.) inbreds was used to investigate the inheritance of photoperiodic response and the role of this response in adaptation to high latitudes. Days from emergence to flowering increased for six of the inbreds and all of the hybrids as the photoperiod was increased from 14 to 22 hours. The photoperiodic response was divided into a basic vegetative phase, which is the time to flowering under ideal photoperiod conditions, and a photoperiodinduced phase. The maximum optimal photoperiod was the longest photoperiod at which no photoperiodinduced delay of flowering-time was observed; the slope of the photoperiod response was the photoperiod sensitivity.

Incomplete dominance for decreased basic vegetative phase (BVP) was observed and an inheritance analysis of BVP produced values for the diallel that were very similar to those obtained previously for flowering-time in field trials. Heritabilities were high for the basic vegetative phase and low for other photoperiod characteristics. Specific combining ability effects were significant for photoperiod sensitivity and maximum optimal photoperiod; reciprocal effects were not significant. General combining ability (GCA) efffects for the basic vegetative phase were correlated with GCA effects for flowering time from field trials in Alberta. For a photoperiod similar to that of 50° N Lat, the average photoperiod-induced delay in floweringtime of the diallel hybrids was 1.5 days. Thus, photoperiod is of only minor importance in the developmental adaptation of the early maturing maize genotypes examined as flowering-time in field trials was closely related to BVP alone.

Key Words: Zea mays L. • Corn • Short-day plant • Flowering • Basic vegetative phase • Photoperiod sensitivity

² Graduate assistant, biology department, Univ. of Calgary, Calgary, Alberta, and crop physiologist, Agriculture Canada Research Station, Lethbridge.

Received for publication September 29, 1980.