Moisture Effects on the Morphology of Ears, Cobs and Kernels of a South-western U.S. Maize (Zea maysL.) Cultivar, and Implications for the Interpretation of Archaeological Maize

Abstract

Studies of the relative effects of growing conditions on specific maize (Zea maysL.) characters enhance interpretation of archaeological maize specimens. To understand better the contribution of moisture as a source of maize variation, this study documents morphological variability of ear, cob and kernel characters by examining a single south-western U.S. cultivar (Tohono O'odham flour maize) grown in 2 consecutive years under five controlled irrigation treatments. Variability in timing and amounts of irrigation water, as well as differences in the timing of rain between the 2 years, resulted in several statistically significant differences in morphological characters. Particularly relevant to the south-western archaeological record of predominantly dryland farming, data from the treatment irrigated only at planting demonstrated differences in maize morphology and grain yield attributable primarily to variability in rain. One character generally recorded on archaeological specimens, row number, was among those least affected by irrigation treatment and rain timing. Cupule width, another often recorded archaeological character, was moderately affected by moisture. For the combined 2-year experiment, characters listed in order from least to most affected were: kernel weight, pith diameter, row number, kernel volume, ratio of kernel width to kernel length, ratio of ear diameter to ear length, kernel thickness, cupule depth, ratio of kernel thickness to kernel length, ear diameter, ear weight, cupule width, cob diameter, ear length, rachis segment length, kernel length, and kernel width. This single cultivar study complements earlier studies of environmental effects on the morphology of maize characters. To determine if moisture effects can mask race-identifying characters, additional controlled-environment studies of other south-western maize cultivars should be conducted. The contribution of moisture, either as irrigation treatment or rain, to reproductive part morphology and grain yield must be considered in the interpretation of archaeological maize.