Monoploid Frequencies in a Commercial Double Cross Hybrid Maize, and in Its Component Single Cross Hybrids and Inbred Lines.

ARTHENOGENETIC development of the egg in maize under the stimuP lus of pollination and normal endosperm development has been noted by RANDOLPH (1939), STADLER (1949), FORTUNO (1948) and others. Data on the frequency of haploidy are meager. RANDOLPH discovered 23 parthenogenetic diploids among 17,165 individuals in the progeny of tetraploid maize, a frequency of about 1:’750. EINSET (1942) found 2 monoploids in 1916 plants in the progenies of trisomic plants pollinated by normal diploids; a frequency of 1:958. STADLER obtained a frequency of about 1: 100 in a diploid multiple recessive tester, which is the highest incidence of haploidy reported in maize, perhaps 20 times the supposed average frequency. Monoploid maize is useful as a source of interesting experimental material, either directly or through its derivatives, and also as a source of homozygous diploids for breeding purposes. Since gametes can be sampled directly in monoploids, if such plants can be obtained in sufficient number and, through doubling of the somatic chromosome complement or interference with the meiotic mechanism, rendered sufficiently fertile to assure seed production, their use in a breeding program in any open-pollinating crop should be of considerable practical importance (see STADLER 1949). The present study is concerned with the incidence of monoploids, of maternal origin, in the progenies of a commercial double cross hybrid, and in its component single cross hybrids and inbred lines when pollinated by four unrelated pollen stocks.