PERENNIALISM IN ZEAl

ETRAPLOID perennial teosinte, Zea psrennis (Hitchc. ) Reeves and ManTgelsd. is the only close relative of the annual Zea, including maize and 2n teosinte, that has the ability to regrow after producing seed. The other Zea, like most annuals, die during seed maturation. The tetraploid form retains totipotency in basal axillary buds and branches throughout the period when the older culms produce flowers and fruit. Not only do the lateral buds retain juvenility, but perennialism is also insured by the development of a horizontal system of stems, mostly. subterranean. These are rhizomes in the purest botanical sense, having scale or reduced leaves, adventitious roots, axillary buds and erect phases. In a form which otherwise perfectly shares a common morphology with 2n annual teosinte and (excepting tetraploidy) shares a common karyotype with both maize and annual teosinte, it is surprising that the highly developed morpho-physiological differences conferring perennialism are unique and unbridged by intermediate forms. In view of the widespread use made of maize both in genetics and agronomy, much might be gained by a knowledge of the cytogenetic and physiological basis of perennialism in an organism from which genes can be easily transferred to maize by crossing over. Perennial teosinte was discovered in 1910 near Guadalahara, Mexico by A. S. HITCHOCK and was collected 10 years later by COLLINS and KEMFTON (COLLINS 1921). The original clone has since been maintained by vegetative propagation in the United States (RANDOLPH 1955). This plant has been the subject of several genetic investigations of its pairing affinities and crossing-over characteristics with maize chromosomes (COLLINS and LONGLEY 1935; LONCLEY 1924, 1934, 1937; EMERSON 1929; EMERSON and BEADLE 1930, 1932; SHAVW 1962a,b, 1963; MANCELSDORF and REEVES 1939). Even though many years ago COLLINS (1921) wrote, ‘ I . . . it was at once appreciated that new forms, of possible economic as well as of great scientific interest, would result if living plants of this perennial [teosinte] could be obtained and if crosses with maize could be affected,” intensive studies of the cytogenetics of perennialism have apparently not been reported. RANDOLPH (1955) tried cursorily to obtain parthenogenetic diploids of perennial teosinte by a process similar to the methods commonly used to derive reduced parthenotes (monoploids) from maize, possibly as a preliminary step to a study of the inheritance of perennialism. Of the two diploid parthenotes recovered by him, however, one proved inviable while young, and the other died after producing abortive flowers, at the same age as companion plants of annual teosinte.