Cytology and Morphology of Maize‐Tripsacum Introgression1

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Abstract
Intergeneric hybrid derivatives of a cross between Zea mays L. and tetraploid Tripsacum dactyloides (L.) L. (2n =72) were compared cytologically and morphologically with a maize genetic stock. The objective of this study was to detect genetic transfers from Tripsacum into the maize genome that might have occurred in the backcross generations. Seven backcrosses to maize were required to eliminate either all the Tripsacum (Tr) chromosomes or all but one pair of the Tr chromosomes. Thirty‐three morphological characters were used to differentiate three groups of plants: (a) lines carrying one pair of Tr chromosomes plus 20 maize chromosomes; (b) lines of fully recovered maize with 20 chromosomes; and (c) a maize genetic stock control. The 22‐chromosome plants clustered as a sharply distinct but variable group. The characters by which they differed most from 20‐chromosome maize were: reduced cob length; increased number of nodes bearing ear shoots and number of ears at a node; increased cupule depth and size; decreased pubescence of the cupule; increased male spikelet pedicel length; increased frequency of tassel‐tipped ears; reduced diameter of the cob pith; and increased caryopsis abortion. These characters show obvious genetic influence from Tr chromosomes as well as Zea characters not present in the original maize parent. The 20‐chromosome recovered maize lines were generally intermediate between the tripsacoid group and standard maize in morphology. The F values for between‐group comparisons were highly significant, and the study verified genetic exchange between the two genomes.

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