Chemical induction of apomictic seed formation in maize

Silks of 18 maize (Zea may L.) F1 hybrids were treated with different combinations of 9 growth regulators, colchicine, and dimethyl sulfoxide (DMSO) for the purpose to induce apomixis (agamospermy) in 1988 and 1989. Hybrid K301 × K303 gave the highest (0.36%) average frequency of seed induction among the hybrids. The most effective treatments were DMSO, gibberellic acid plus 6-benzyl aminopurine (6-BA), and DMSO plus methanesulfonic acid. Individually, the highest frequency of seed induction was 1.4% for hybrid K731×K306 when treated with a-naphthalene acetic acid (NAA)-zeatin mixture. The frequency of seed induction seemed to depend partially on the interaction between chemicals and hybrids. Cytological observation of root-tip cells indicated that the majority of the seeds obtained were diploid, some were mixoploid, and a few were haploid. Diploid plants from induced seeds from the same parent were morphologically uniform and resembled the parent. Variations in plant and ear heights were comparable to those of the hybrid parent. Cytological and morphological investigations suggested that the chemically induced seeds originated mainly from somatic tissue but occasionally came from reduced cells in the embryo sac, leading to haploids. The results showed that chemical induction of adventitious embryony in maize hybrids is possible, but the more effective chemicals, their concentrations, and ways of application for increasing the frequency of seed induction need to be explored for practical use.